i am currious to know if i might encounter any problems with a transfer switch..
i am still putting together my solar project here, but i now have a concern.
my inverter will be in use most of the time, it is a pure sinewave.
my load will be typical consumer electronics and lights (CFL's halogen etc)
the transfer switch will switch over to mains power if my battery supply should get too low..then back on later when the batterys have charged up.
is there gonna be a surge problem with one AC switching over to another AC ? at same voltage ? like a buck or boost type deal ?
i am planning to use a DPDT relay
i hope i am asking this question right...
contacts will be wired up like this...
NO = inverter
NC = commercial power
common = load
AC transfer switch question
Switching Possibilities
I assume you want to switch between the AC output of the inverter and the AC mains, doing AC switching. This can be complex. The switching has to be a BREAK before MAKE. Otherwise if you parallel the inverter output with the mains, all sorts of bad things can happen. If the inverter output is paralleled with the AC mains and the AC signals are not in sync, voltages will be unpredictable. Equipment can be damaged, people could be hurt or die. It can also be possible to back feed the AC mains during a power failure. Using a BREAK before MAKE relay should accomplish this isolation but is not what I would do. In the case of an inverter failure or possible maintenance, you can manually switch the AC side between inverter and mains using a set of switches that BREAKS the inverter output connection then allows the MAKE of the mains connection. You mention using the inverter most of the time, so why not use it ALL the time?
Let me suggest an alternative; use an AC to DC power supply instead. Fire up the input to the DC supply, parallel it to the solar/battery system, disconnect the solar/battery system and let it charge solar only. Alternately you could simply parallel them and have the DC supply aide in the recharge of the batteries should you experience a number of days of cloudy weather. You will be using the inverter full time with this method but you won't see a glitch. Blocking diodes are likely in place so the solar cells/charge controllers won't see the DC supply. Thus you could simply connect up the DC supply with the appropriate blocking diodes and only have to switch on the AC input to it as needed.
If you really think there is a need to isolate the solar/battery system from the inverter, paralleling a DC supply would work except you would need a way to disconnect the batteries and connect the power supply to the inverter. Still I'd recommend paralleling the DC supply for a few seconds to the battery before disconnecting the batteries from the inverter.
Large data centers have generator backup in most cases. But the generator feeds a UPS system. In the enterprise UPS systems the AC is converted to DC and is in parallel to the batteries. The UPS inverter runs 24/7/365.
If you wish for me to put my idea in a schematic form, please let me know.
Let me suggest an alternative; use an AC to DC power supply instead. Fire up the input to the DC supply, parallel it to the solar/battery system, disconnect the solar/battery system and let it charge solar only. Alternately you could simply parallel them and have the DC supply aide in the recharge of the batteries should you experience a number of days of cloudy weather. You will be using the inverter full time with this method but you won't see a glitch. Blocking diodes are likely in place so the solar cells/charge controllers won't see the DC supply. Thus you could simply connect up the DC supply with the appropriate blocking diodes and only have to switch on the AC input to it as needed.
If you really think there is a need to isolate the solar/battery system from the inverter, paralleling a DC supply would work except you would need a way to disconnect the batteries and connect the power supply to the inverter. Still I'd recommend paralleling the DC supply for a few seconds to the battery before disconnecting the batteries from the inverter.
Large data centers have generator backup in most cases. But the generator feeds a UPS system. In the enterprise UPS systems the AC is converted to DC and is in parallel to the batteries. The UPS inverter runs 24/7/365.
If you wish for me to put my idea in a schematic form, please let me know.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!
I don't tHink I would use a generic 'relay' for the transfer. With inductive loads and starting currents its life may be quickly limited.
A contactor is in order, with heavy contacts, wide gaps for arc quenching and flash suppression. None of these are features in 'relays'.
Additionally, the movable contact block on a contactor is arranged, with very wide contact spacing, so there are no accidental cross connections due to contact bounce during switching.
I believe that friend might still has a used transfer relay, from a stage lighting system. It is multi pole, with big contats. If you are interested, I'll get the details.
Len
A contactor is in order, with heavy contacts, wide gaps for arc quenching and flash suppression. None of these are features in 'relays'.
Additionally, the movable contact block on a contactor is arranged, with very wide contact spacing, so there are no accidental cross connections due to contact bounce during switching.
I believe that friend might still has a used transfer relay, from a stage lighting system. It is multi pole, with big contats. If you are interested, I'll get the details.
Len
-
dacflyer
- Posts: 4749
- Joined: Fri Feb 08, 2002 1:01 am
- Location: USA / North Carolina / Fayetteville
- Contact:
jolly said... You mention using the inverter most of the time, so why not use it ALL the time?
i plan to..unless theres a few days of no sun...
the relay is a break before make..
the coil will be controlled by a battery meter, with set points that will control the coil of the relay.. i want the transfer relay to be automatic.
and yes i know all about the safety deals so no worries..
the inverter will never be able to make contact with commercial power.
a battery charger is not really an option for me either..because of the cost. i'd need at least a 100 amp charger , and not some el cheapo auto charger either.
Lenp >> right on using a contactor,,this is what i actually have..
POTTER & BRUMFIELD P/N PRD-11DG1-24 25amp
http://catalog.tycoelectronics.com/TE/b ... D-11DG1-24
i might be interested in the one you have perhaps,,but i need something with a 24 volt coil
i plan to..unless theres a few days of no sun...
the relay is a break before make..
the coil will be controlled by a battery meter, with set points that will control the coil of the relay.. i want the transfer relay to be automatic.
and yes i know all about the safety deals so no worries..
the inverter will never be able to make contact with commercial power.
a battery charger is not really an option for me either..because of the cost. i'd need at least a 100 amp charger , and not some el cheapo auto charger either.
Lenp >> right on using a contactor,,this is what i actually have..
POTTER & BRUMFIELD P/N PRD-11DG1-24 25amp
http://catalog.tycoelectronics.com/TE/b ... D-11DG1-24
i might be interested in the one you have perhaps,,but i need something with a 24 volt coil
If you could somehow synchronize the phase of the inverter with the line it would be easier because the voltage difference between the two sources would be minimal (ideally 0) making relay switching arc free. Also under that condition, it might be possible (not necessarily safe) to actually parallel them for more current.
I'm trying to think of a way you can directly mix or add the power of the mains and inverter through a transformer (still need 0 deg phase) but I'v never heard of that anyway (at least not for power, maybe small signals) in practice.
I'm trying to think of a way you can directly mix or add the power of the mains and inverter through a transformer (still need 0 deg phase) but I'v never heard of that anyway (at least not for power, maybe small signals) in practice.
Hello,
I was going to mention something like that too
A phase locked loop can help here, but there also has to
be a way to control the inverter with it. That may be hard
to do with store bought units. When you design the inverter
yourself you have control over that aspect too, but not everyone
wants to do that either.
The standard way to handle this is to use a contactor. The contactor
will have break before make contacts and that will help solve the
problem. Using a standard relay can cause all sorts of problems,
and ive seen inverters blow up (transistors smoke) because the
line gets fed into the output for a short period. That's not good.
A contactor is made for this however.
Another possibilty is if your application can stand a delay in the
second source being switched in, you can use two relays and sync
them up. Have one relay turn off, then a delay, then have some
feedback to ensure that it has turned off, then turn on the second
relay. This will solve the problem also but the load has to be able
to tolerate the delay.
You might also look into two solid state relays, where they use
devices like scr's inside. Again you would turn one off, verify that
it is off, and then turn the other one on.
A fuse in the output of the inverter is a must too, before the relays
or whatever.
There is also another problem that comes up...
this is that when the line goes sour it could be at +90 degrees in phase,
and the inverter is at -90 degrees in phase, and the relay turns off
fine and the other relay turns on, but now the load sees perhaps an
instantaneous voltage change that goes from 170 volts to -170
volts in perhaps 100us. This isnt good either. The only solutions
i think is to either phase lock the inverter to the line, or else make
sure the inverter goes through the zero crossing where the dv/dt
is either positive or negative, and dont close the relay until the
inverter goes through the same period in it's phase (wont always
be synced, but that's life). This means the load could possibly
loose a whole cycle of operation, but the alternative will beat the
load with a nasty current spike if it's not inductive.
There are ways to make some loads tolerate more dead time too,
to allow for more relay delays. For example, with a bridge rect
you can increase the size of the filter caps sometimes.
A question then would be, what kind of load is this driving and
how much dead time can it tolerate?
I was going to mention something like that too
A phase locked loop can help here, but there also has to
be a way to control the inverter with it. That may be hard
to do with store bought units. When you design the inverter
yourself you have control over that aspect too, but not everyone
wants to do that either.
The standard way to handle this is to use a contactor. The contactor
will have break before make contacts and that will help solve the
problem. Using a standard relay can cause all sorts of problems,
and ive seen inverters blow up (transistors smoke) because the
line gets fed into the output for a short period. That's not good.
A contactor is made for this however.
Another possibilty is if your application can stand a delay in the
second source being switched in, you can use two relays and sync
them up. Have one relay turn off, then a delay, then have some
feedback to ensure that it has turned off, then turn on the second
relay. This will solve the problem also but the load has to be able
to tolerate the delay.
You might also look into two solid state relays, where they use
devices like scr's inside. Again you would turn one off, verify that
it is off, and then turn the other one on.
A fuse in the output of the inverter is a must too, before the relays
or whatever.
There is also another problem that comes up...
this is that when the line goes sour it could be at +90 degrees in phase,
and the inverter is at -90 degrees in phase, and the relay turns off
fine and the other relay turns on, but now the load sees perhaps an
instantaneous voltage change that goes from 170 volts to -170
volts in perhaps 100us. This isnt good either. The only solutions
i think is to either phase lock the inverter to the line, or else make
sure the inverter goes through the zero crossing where the dv/dt
is either positive or negative, and dont close the relay until the
inverter goes through the same period in it's phase (wont always
be synced, but that's life). This means the load could possibly
loose a whole cycle of operation, but the alternative will beat the
load with a nasty current spike if it's not inductive.
There are ways to make some loads tolerate more dead time too,
to allow for more relay delays. For example, with a bridge rect
you can increase the size of the filter caps sometimes.
A question then would be, what kind of load is this driving and
how much dead time can it tolerate?
LEDs vs Bulbs, LEDs are winning.
-
dacflyer
- Posts: 4749
- Joined: Fri Feb 08, 2002 1:01 am
- Location: USA / North Carolina / Fayetteville
- Contact:
well as i said earlier... lights ( CFL's and halogens ) and consumer electronics..
theres no way i have control of phase syncing
in the earlier post i gave, i shown i was using a small contactor type DPDT
there is almost 1/8" gap between contacts..
switching from inverter to commercial power was the concern..
i was concerned about any spikes or surges from out of phase switch overs...if that would be of any real concern
i have tons of 150volt MOVS i could use if that might be of help.
i also have access to some R/C items also..
theres no way i have control of phase syncing
in the earlier post i gave, i shown i was using a small contactor type DPDT
there is almost 1/8" gap between contacts..
switching from inverter to commercial power was the concern..
i was concerned about any spikes or surges from out of phase switch overs...if that would be of any real concern
i have tons of 150volt MOVS i could use if that might be of help.
i also have access to some R/C items also..
Phase control,
A lifetime ago, while overseas in the military I saw large generators that 'assisted' during brown outs. They had mechanically rotating field coils that were constantly being adjusted to keep their output in phase with the grid. Motors, relays and differential control circuits were the norm.
Relevent, probably not; Interesting, maybe.
Len
A lifetime ago, while overseas in the military I saw large generators that 'assisted' during brown outs. They had mechanically rotating field coils that were constantly being adjusted to keep their output in phase with the grid. Motors, relays and differential control circuits were the norm.
Relevent, probably not; Interesting, maybe.
Len
Hi again,dacflyer wrote:well as i said earlier... lights ( CFL's and halogens ) and consumer electronics..
theres no way i have control of phase syncing
in the earlier post i gave, i shown i was using a small contactor type DPDT
there is almost 1/8" gap between contacts..
switching from inverter to commercial power was the concern..
i was concerned about any spikes or surges from out of phase switch overs...if that would be of any real concern
i have tons of 150volt MOVS i could use if that might be of help.
i also have access to some R/C items also..
Sorry maybe i missed that.
What you could do however is the suggestion that you monitor the
line frequency (waves) using perhaps a comparator (cheap) and
keep track of what phase the line (or inverter) is, and when it
crosses through zero (x axis) you figure out where your other
source (inverter or line) is and decide when you can switch to
the new source (another comparator). This would be a fairly simple
circuit which would not require a uC, just some LM339 comparators,
in fact, one ic package, cost around 50 cents, and some resistors
and maybe a few diodes. This would work pretty well for loads that
are not highly inductive.
I think worst case is that they are like 1 degree out of phase (remember
we arent controlling the phase, just monitoring it now), in which case
the load would not see any power for one cycle, which probably isnt too
bad.
Of course an even simpler scheme is to just wait 1 full second after
switching off the first source, then after that 1 second turn on the
second source (with another relay). The power will drop out for a
full second, but if it only happens once in a while maybe that will
be ok.
BTW, do you know the response time of your relays or contactors?
If you turn one relay off and use the N.O. contacts to turn *on* the
second relay maybe enough time has passed anyway to not worry
about the phasing. This would mean the first relay actually turns on
the second relay (along with another control mechanism).
LEDs vs Bulbs, LEDs are winning.
Well, I didn't really expect phase synching to be a practical solution.
If voltage spiking is now your major concern, in addition to all that switching advice from MrAl, add to that a common Surge Supressor. Get a high energy one intended for installation in the breaker panel for point of source or you can get some for point of load use ( extension cord kind).
I don't think the lamps will care much about brownouts, its spikes that will blow bulbs.
You could also do away with the AC all together and favor DC lighting sources thus eliminating the efficiency loss of the inverter. That may not be practical either if you are using existing house wire to distribute the power. But thats a whole different track now.
How many watts total are you trying to power. Seems that a UPS already does this in reverse. THe question is How? I found this link, looks like a good one
http://www.smps.us/uninterruptible-power-supply.html
If voltage spiking is now your major concern, in addition to all that switching advice from MrAl, add to that a common Surge Supressor. Get a high energy one intended for installation in the breaker panel for point of source or you can get some for point of load use ( extension cord kind).
I don't think the lamps will care much about brownouts, its spikes that will blow bulbs.
You could also do away with the AC all together and favor DC lighting sources thus eliminating the efficiency loss of the inverter. That may not be practical either if you are using existing house wire to distribute the power. But thats a whole different track now.
How many watts total are you trying to power. Seems that a UPS already does this in reverse. THe question is How? I found this link, looks like a good one
http://www.smps.us/uninterruptible-power-supply.html
-
dacflyer
- Posts: 4749
- Joined: Fri Feb 08, 2002 1:01 am
- Location: USA / North Carolina / Fayetteville
- Contact:
MrAl >> i have no way or how to control any of this,,,too complicated for me to make anything that will control all that ,
i do not know the responce of the contactor i have..there is no info i seen other than the data link i posted earlier.
and the contactor i have has about 1/8" gap between contacts
so during switchover i should have just an instantainous blink of switch over..just enough to let me know it happened..
i see now, i think i may have to make a mock up with 2 generators i have here, and seek results myself,,
i was just looking for a simple answer to my problem...
haklesup >> my inverter is a Xantrex "sine wave inverter 1800 watts"
model 1800/24 this model does not have a transfer relay..
i seen other models that do have that feature,,but they operate like a UPS
always on line power , and if failed, then the inverter turns on..
haven't seen any that are always on battery, then if failed the commercial power kicks on.
anyway.. thats all for now..
i do not know the responce of the contactor i have..there is no info i seen other than the data link i posted earlier.
and the contactor i have has about 1/8" gap between contacts
so during switchover i should have just an instantainous blink of switch over..just enough to let me know it happened..
i see now, i think i may have to make a mock up with 2 generators i have here, and seek results myself,,
i was just looking for a simple answer to my problem...
haklesup >> my inverter is a Xantrex "sine wave inverter 1800 watts"
model 1800/24 this model does not have a transfer relay..
i seen other models that do have that feature,,but they operate like a UPS
always on line power , and if failed, then the inverter turns on..
haven't seen any that are always on battery, then if failed the commercial power kicks on.
anyway.. thats all for now..
Re: AC transfer switch question
Greetings dacflyer,
Sounds like you are trying to live "off-grid" with
solar power and storage batteries.
Typically solar power systems are used to supplement
utility power (because the sun doesn't shine all the
time).
In these cases the inverter used to convert solar
generated DC power is "grid-tied" and always on.
The inverter is sync'd to the grid, and will also
shutdown if the grid is lost. This is a safety feature
to stop the solar generated power from energizing
the utility lines and causing a safety hazard to
utility line workers that may not know the lines
are powered "backwards" from a customer.
For safety these systems also have an AC Disconnect
switch for servicing the solar and inverter off grid.
UPS (Uninterruptable Power Units) are designed
to replace the utility power during a service outage.
The always on variety operate with AC-DC-AC
configuration, meaning the utility AC is converted
to DC to charge batteries, and reconverted to AC
to power the load. If the utility power is lost the
load is then powered from the battery via the
inverter without missing a beat.
Homeowners in severe weather climates use
back up generators that replace the AC utility
if lost (due to storms etc.). These systems
have an interlocking changeover switch that
prevents the genertor from feeding the AC
utility. The switchover is not seamless and
requires that the generator is started and
brought up to speed (line frequency first).
It would also be prudent to disconnect all
electronic devices from the AC power while
the generator is being adjusted and connected.
Before you put your system on-line I think you
should get your local utility to sign off on the
work.
for the equipment running from it. In most cases
this should not be an issue, as most appliances
and lights do not care about reasonable surges
or brown outs.
An automatic changeover is probably the worst
you could have, as there will be no warning of
the switch over and in your plan the inverter
will be taken off line again when the battery
voltage drops. Computers and many home
appliances that are always powered (newer TVs,
cable boxes, computers, and even furnace
controls) will be upset by frequent power
brown outs (caused by a mechanical relay
back up system).
If it were me I'd take a close look at inverters
designed for UPS, starting with off-grid solar
vendors first.
Comments Welcome!
Peter
Sounds like you are trying to live "off-grid" with
solar power and storage batteries.
Typically solar power systems are used to supplement
utility power (because the sun doesn't shine all the
time).
dacflyer wrote: my inverter will be in use most of the time, it is a pure sinewave. my load will be typical consumer electronics and lights (CFL's halogen etc)
the transfer switch will switch over to mains power if my battery supply should get too low..then back on later when the batterys have charged up.
In these cases the inverter used to convert solar
generated DC power is "grid-tied" and always on.
The inverter is sync'd to the grid, and will also
shutdown if the grid is lost. This is a safety feature
to stop the solar generated power from energizing
the utility lines and causing a safety hazard to
utility line workers that may not know the lines
are powered "backwards" from a customer.
For safety these systems also have an AC Disconnect
switch for servicing the solar and inverter off grid.
UPS (Uninterruptable Power Units) are designed
to replace the utility power during a service outage.
The always on variety operate with AC-DC-AC
configuration, meaning the utility AC is converted
to DC to charge batteries, and reconverted to AC
to power the load. If the utility power is lost the
load is then powered from the battery via the
inverter without missing a beat.
Homeowners in severe weather climates use
back up generators that replace the AC utility
if lost (due to storms etc.). These systems
have an interlocking changeover switch that
prevents the genertor from feeding the AC
utility. The switchover is not seamless and
requires that the generator is started and
brought up to speed (line frequency first).
It would also be prudent to disconnect all
electronic devices from the AC power while
the generator is being adjusted and connected.
Before you put your system on-line I think you
should get your local utility to sign off on the
work.
Yes, your system will have several problemsdacflyer wrote: is there gonna be a surge problem with one AC switching over to another AC ? at same voltage ? like a buck or boost type deal ?
i am planning to use a DPDT relay
for the equipment running from it. In most cases
this should not be an issue, as most appliances
and lights do not care about reasonable surges
or brown outs.
An automatic changeover is probably the worst
you could have, as there will be no warning of
the switch over and in your plan the inverter
will be taken off line again when the battery
voltage drops. Computers and many home
appliances that are always powered (newer TVs,
cable boxes, computers, and even furnace
controls) will be upset by frequent power
brown outs (caused by a mechanical relay
back up system).
If it were me I'd take a close look at inverters
designed for UPS, starting with off-grid solar
vendors first.
Comments Welcome!
Peter
-
dacflyer
- Posts: 4749
- Joined: Fri Feb 08, 2002 1:01 am
- Location: USA / North Carolina / Fayetteville
- Contact:
Re: AC transfer switch question
Bigglez wrote:Greetings dacflyer,
Sounds like you are trying to live "off-grid" with
solar power and storage batteries.
not totally, just most of my 120volt circuits..
Typically solar power systems are used to supplement
utility power.
i know this much.
dacflyer wrote: my inverter will be in use most of the time, it is a pure sinewave. my load will be typical consumer electronics and lights (CFL's halogen etc)
the transfer switch will switch over to mains power if my battery supply should get too low..then back on later when the batterys have charged up.
In these cases the inverter used to convert solar
generated DC power is "grid-tied" and always on.
The inverter is sync'd to the grid, and will also
shutdown if the grid is lost. This is a safety feature
to stop the solar generated power from energizing
the utility lines and causing a safety hazard to
utility line workers that may not know the lines
are powered "backwards" from a customer.
this will not be a problem, as there will be no way for the inverter circuit to connect with the commercial circuit..
For safety these systems also have an AC Disconnect
switch for servicing the solar and inverter off grid.
UPS (Uninterruptable Power Units) are designed
to replace the utility power during a service outage.
The always on variety operate with AC-DC-AC
configuration, meaning the utility AC is converted
to DC to charge batteries, and reconverted to AC
to power the load. If the utility power is lost the
load is then powered from the battery via the
inverter without missing a beat.
i know how inverters operate, i am not new to this.
Homeowners in severe weather climates use
back up generators that replace the AC utility
if lost (due to storms etc.). These systems
have an interlocking changeover switch that
prevents the genertor from feeding the AC
utility. The switchover is not seamless and
requires that the generator is started and
brought up to speed (line frequency first).
It would also be prudent to disconnect all
electronic devices from the AC power while
the generator is being adjusted and connected.
Before you put your system on-line I think you
should get your local utility to sign off on the
work.
my system will not be grid tied,,nor does my utility company offer this solution, otherwise i'd have done this already..
Yes, your system will have several problemsdacflyer wrote: is there gonna be a surge problem with one AC switching over to another AC ? at same voltage ? like a buck or boost type deal ?
i am planning to use a DPDT relay
for the equipment running from it. In most cases
this should not be an issue, as most appliances
and lights do not care about reasonable surges
or brown outs.
there will not be any brown outs, with what i want to do, if there was any brown out, it'd be fromthe commercial power..
An automatic changeover is probably the worst
you could have, as there will be no warning of
the switch over and in your plan the inverter
will be taken off line again when the battery
voltage drops. Computers and many home
appliances that are always powered (newer TVs,
cable boxes, computers, and even furnace
controls) will be upset by frequent power
brown outs (caused by a mechanical relay
back up system).
i have UPS's on my sensitive equpiment such as computers and tv's etc.
If it were me I'd take a close look at inverters
designed for UPS, starting with off-grid solar
vendors first.
i have looked, all the inverters i have seen only run normally on standby
(commercial power, until there is a failure, then the inverter kicks in,,as i stated, i want my system to run on inverter all the time,,then switch over to commercial power if the batterys should happen to get to low..but in no way will the inverter ever be connected to commercial power.
Comments Welcome!
Peter
Hey Dac, now I have two suggestions. For your approach of switching the AC at the load end. You could parallel an additional low cost automotive style inverter. These usually have a low battery cutoff circuit which also lights an LED. You could easily use that LED to signal a transfer relay. and use its 100W AC output for whatever you want.
But that new guy had a good point at the end about not knowing when it would switch over and the possibility of being surprised or disappointed by the glitch. That got me thinking.
Why not put the switch on the DC side of the inverter and let the inverter power the load 100% of the time. You could sense the current from the solar array using a shunt (or DC voltage of your bank) and parallel an AC-DC power supply (probably a switcher) with similar current output to the solar array or whatever you judge to be sufficient. This way you can maintain a more stable charge in your battery bank potentially extending its life.
This naturally opens the door to the method one would use to decide when and how much to charge via the line to obtain max efficiency and battery life. I haven't thought it through that far yet. I do know you would be throwing away the efficiency loss of the DC supply as compared to the AC transfer method that plus the cost of this supply vs a transfer switch. If that mode is as infrequent as you say, it might be tolerable. At least this way you get glitch free AC all the time making it suitable for far more than just lighting.
BTW, When I say Transfer switch, I mean any relay rated for the load controlled by a circuit that senses some condition. for simplicity
But that new guy had a good point at the end about not knowing when it would switch over and the possibility of being surprised or disappointed by the glitch. That got me thinking.
Why not put the switch on the DC side of the inverter and let the inverter power the load 100% of the time. You could sense the current from the solar array using a shunt (or DC voltage of your bank) and parallel an AC-DC power supply (probably a switcher) with similar current output to the solar array or whatever you judge to be sufficient. This way you can maintain a more stable charge in your battery bank potentially extending its life.
This naturally opens the door to the method one would use to decide when and how much to charge via the line to obtain max efficiency and battery life. I haven't thought it through that far yet. I do know you would be throwing away the efficiency loss of the DC supply as compared to the AC transfer method that plus the cost of this supply vs a transfer switch. If that mode is as infrequent as you say, it might be tolerable. At least this way you get glitch free AC all the time making it suitable for far more than just lighting.
BTW, When I say Transfer switch, I mean any relay rated for the load controlled by a circuit that senses some condition. for simplicity
Who is online
Users browsing this forum: Majestic-12 [Bot] and 63 guests