10) I've tested the Allegro sensors in just one other circuit. It worked fine. The readings I was getting made sense when compared to the ones I was getting with my clamp meter.
The OR'ing of op-amps sounds promising, but I'd like to set a number of voltage levels (float, absorb, equalize, etc). If I change battery brands, these all will change, so it would be nice to set them in software. Were I to pull this flexibility idea out of the equation, Maxim's got a chip for managing FLA charging that I could splice in somehow, but where's the fun in that?
12) I have 100Ah batteries. The manuf. recommends charging at a max of C/5. So I think that makes my max charge rate 20a. However, with the system under load (like when the well pump's running), I'd like to be able to charge at up to 20 amps while "keeping up" with the load. This is why I mention positioning the Allegro sensors such that the current flowing into and out of each battery is isolated from the current moving through the entire system. That is to say, if the inverter is pulling 20a from each battery and the output of the alternator (for a particular battery) is 40a, that the sensor reads 20a (just the part that the battery is seeing). Make sense?
Thanks again!
Hi again,
Ok, so we will say about 20 amps max. One little question:
Do you happen to know the ratio of current through the field winding to alternator current?
In other words, if you have say 20 amps charging the battery how much current is then flowing
through the field winding? [This information helps build the control law for studying the feedback system]
The OR'ing of the outputs is unrelated to the set points. You would still be able to set the voltage at any
time and also the max current (current limit for charging).
The current sensors have output that centers at Vcc/2 right? That means they are biased at one half
the supply voltage. Do you happen to have any that are not biased like that? Those are probably
dual polarity when we really only need single polarity, although they would still work. The set point
dig pot would be biased also to get the max range of adjustment.
The monitoring of the battery current would be directly in line with one battery terminal. That means
the current through the battery would be measured. If there is no load, the battery will go up to say
20 amps charge (if that is the set point) and maintain that level. If there is a load, the circuit will put
the maximum current into the system in an attempt to put 20 amps through the battery. If there
happened to be 10 amps load then the battery would see 15 amps if the max available was really
25 amps. If 20 amps load, the battery would see 5 amps charge, etc. If the load were greater than
25 amps (we are supposing that 25 is the max the alternator can put out) then the battery
would be discharging at the rate ILoad-25 amps rather than the full load current rate. In this mode
the alternator would be supplying some of the load current but the battery would not be charging.
Note that in this system there is no way to limit the max current coming from the alternator
when there is a significant load. To do that, another current sensor and op amp would be required.
So another question would be:
Do you really have to limit the current out of the alternator, or can you let that go to as high as
it can produce when there is a significant load on the system?
The circuit to do all of this is surprisingly simple if you would like to see a schematic.
That paper on the linear regulators was interesting, but if you look at a simple op amp circuit
and try to develop the math for that circuit that turns out to be very informative and can shed
much light on how most linear regulators work. The feedback and how they handle that feedback
is the whole key to the linear regulator. How it is possible to use an amplifier with a very very
high gain (op amp) in a circuit to control the output while measuring that output. A 'block'
diagram is very helpful in understanding this kind of thing and it gets very simple that way.
I can post a block diagram if you like.
Actually a block diagram of your project wouldnt hurt either i guess.
LEDs vs Bulbs, LEDs are winning.