AC-Adapter for Battery operated device

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haklesup
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Re: AC-Adapter for Battery operated device

Post by haklesup » Wed May 21, 2014 2:14 pm

I missed your comment before "I rewired the DC jack directly to the battery terminal (mindful of polarity). I tried seven 12V power supplies ranging from 1A to 4A. Out of these, the only one that worked was the 12V (17A) output of a PC ATX power supply. While this works, it is not a practical solution." I will assume that you do not operate with batteries and the adapter at the same time as one could load the other undesirably

Roughly speaking, A "D" battery should have a discharge current around 1A or more while high performance AA can be 900mA, (not much of a benefit to D anymore, AA used to be worse, D will last longer though) so if you are needing more than 4A to power the printer, perhaps there is another failure you are not aware of. Does it kill batteries quickly and do they get warm while operating.

I would certainly put an ammeter in series between your battery terminal and the positive adapter output and measure supply current at 12VDC to see if it is much less than 1A while idling and no more than 1A while operating.

Another way of evaluating this is if you try the smaller adapters, does the voltage get reduced when you power on. This is a sign that you are exceeding the current output of the supply and ran out of power such that the voltage will fall off (obeying ohms law that's all). Then it should go back to normal when removed from the printer.

Check any diodes close to the battery connection, especially any that seem to be across the pos and neg input terminals. Even putting batteries in backward briefly can stress this protection diode and make it leaky enough to become part of the load. Capacitors near the power input could also become leaky causing supply current requirements to rise. This Reverse power protection diode is normally present on battery operated devices and is often damaged when one attempts what you are doing because all to often it is undersized for power dissipation.

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Lenp
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Re: AC-Adapter for Battery operated device

Post by Lenp » Wed May 21, 2014 2:56 pm

Methinks the printer has been modified. Without accurate information remote help is unlikely to be a success!
Len

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Re: AC-Adapter for Battery operated device

Post by francesco » Wed May 21, 2014 3:23 pm

Lenp wrote:Methinks the printer has been modified. Without accurate information remote help is unlikely to be a success!
Yes, it has been modified and the only mod is the wiring of the DC jack. The only way you can help is if you know how to make this device see the DC power supply as a battery.

Even though DC power comes out of batteries and DC power supplies, there are differences between the two power sources. The battery input of this printer was obviously designed to work only with batteries and I need to know what can I do to make it work with a DC power supply. How difficult is that to understand?

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Lenp
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Re: AC-Adapter for Battery operated device

Post by Lenp » Thu May 22, 2014 5:48 am

What is hard to understand is your obvious frustration.
francesco wrote:The only way you can help is if you know how to make this device see the DC power supply as a battery.
francesco wrote:The battery input of this printer was obviously designed to work only with batteries and I need to know what can I do to make it work with a DC power supply. How difficult is that to understand?
Various members with extensive professional backgrounds are trying to assist YOU and we are not taking custody of the problem. If you want someone to just fix it then be prepared to pay. To help YOU we need information but that has not been provided by you. Frustratiion simply is not a troubleshooting technique and it stands in the way of success.

Now, with that being said.....
I looked at the printer manual online and it does require 8 AA cells. The optional adapter is 9.5v

So, either the manual is wrong or 12v is the absolute maximum and 9.5 is the minimum operating printer voltage, or they boost the voltage inside the printer which is quite unlikely!

With a 2.5 volt voltage range batteries should provide a reasonable run time before they are exhausted.

Cheap AC adapters are typically unregulated and have a higher output voltage than the marking shows. Their rating is valid only when the adapter is providing the rated output current. Switch mode adapters can be better regulated and may be closer to the rated voltage. So if your 12 volt adapter is really much higher then 12 volts there may be a protection circuit in the printer to protect it and keep the smoke from getting out if someone uses a potentially damaging incorrect AC adapter.

Yes, you say the printer was modified but the question is why?
Was it necessary to modify the wiring on the jack because it not work with the original adapter?
(that should have been troubleshooting not a self-redesign)
Did you use an incorrect adapter, when the manual and online informatiion gives the voltage, and damage some components?
If there was other electronic components involved with the power jack they certainly were there for a purpose.
Typically an ac adapter jack has a simple contact that opens the battery connection and provides the external power to the device in place of the batteries. Since Brother sells an adapter, and it works with the printer, then there is something quite simple being missed. It certainly is not rocket science or magic.

Ac power supplies are routinely used to power battery equipment with success. Yes, DC power comes from both batteries and DC power supplies, and there are subtle differences between the two power sources. The differences can be impedence and ripple voltage or noise but, since Brother does it with a rather generic and inexpensive power adapter, I doubt these issues are worthy of consideration. With rare exception battery and power supply voltages are compatible and if the output current is adequate in most all cases they work.

We have asked for current and voltage readings but I haven't seen any yet. If you can't give those I suggest you use a lower voltage adapter to see if it works. I have no comment on the PC power supply working not working ...


Len
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Re: AC-Adapter for Battery operated device

Post by francesco » Thu May 22, 2014 7:09 am

My frustration comes from the fact that you’re not reading everything I typed, you keep referring to the useless manual and you look for what might be in between the lines rather than focusing on the lines.

Yes, it was necessary to modify the wiring on the jack. The special circuit Brother installed was burnt, which I believe I mentioned in an earlier post.

If the fix was simple I wouldn’t be here asking for anything. So save your simple solutions and manual references for somebody else.

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Re: AC-Adapter for Battery operated device

Post by Lenp » Thu May 22, 2014 8:37 am

...
Len

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Lenp
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Re: AC-Adapter for Battery operated device

Post by Lenp » Thu May 22, 2014 8:55 am

I will take your suggestion!
Good luck!
You are on your own....
Len

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haklesup
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Re: AC-Adapter for Battery operated device

Post by haklesup » Thu May 22, 2014 1:25 pm

This unit is a Brother P-Touch 2600. It had a separate circuit board for 12V DC power that fed directly in to the mainboard. This circuit board is now dead, thus, the printer works only on batteries. Besides, if there is a jack, it could be because I added one.
I re-read your posts and the special circuit you are trying to bypass is the internal power supply. It stands to reason that if you induced an overstress in the power supply something else may have been damaged on what it was connected to. While it does seem to work on batteries it still may be consuming a large supply current die to latent damage you have yet to identify. A supply current check with batteries and external supply is a solid troubleshooting check.

The presence of voltage on a circuit board doesn't actually say much. An open circuit will always show applied voltage across it but will deliver no power to the device. Supply current is the real picture of how much power your printer needs.

in principal, an external DC supply (assuming it is good quality and filtered) makes DC electricity that is indistinguishable from a battery. A lower quality older wall wart may have very high ripple due to insufficient capacitor inside, or lower cost half wave rectification. This ripple may be disturbing the printer enough to not function. Measure the AC voltage across the supplies you try. It should be as close to Zero as you can get. A battery should have no ripple voltage at all but a lower quality supply when operated under full load may have as much as 50% ripple. The DMM will give you a clue, an oscilloscope will make it crystal clear.

The only question I have is do the batteries last long or do they die fairly quickly. This would be another sign of high supply current induced by an unidentified failure.

You did not comment on why the internal power supply failed. I would speculate that the unidentified failure that is hypothetically causing high supply current over taxed the original supply until it eventually failed. That initial failure probably still exists and is dogging you now. My experience tells me failures often occur in clusters as one root cause triggers overstress events downstream. Only in interconnect related failures (opens and shorts at assembly level) are you likely to find only one issue.

PS, I am a 25 year experienced EE working in Failure analyses of IC devices. I read between the lines because my experience lets me see volumes there, I assume that is true of many esteemed members left in tis small but passionate forum. Be patient with us and restate your question in different terms or with more detail if you are not getting the answers you need, we do like to help and love a challenge.

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Re: AC-Adapter for Battery operated device

Post by francesco » Thu May 22, 2014 2:39 pm

Thanks, Haklesup.

The printer gets used at least once a week, the power button is a momentary/soft switch so I’m sure it is using a very small amount of power at all times and the batteries were installed a few months ago. So the batteries last a long time.

When I got the printer, it already had a this problem. It came with a 12V power supply and I think it is how that circuit board got damaged.

As of right now, the printer works fine with batteries but DC power supplies detect a short. And, again, the DC power supply is connected directly to the +/- terminals where the batteries would normally be.

I think I have seen this before when trying to attach a DC power supply to a battery operated device that was not provisioned to run with a DC power supply. There has to be something different or missing that is causing the DC power supply to detect a short. Unfortunately, I only have access to a cheap multi-meter.

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Lenp
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Re: AC-Adapter for Battery operated device

Post by Lenp » Thu May 22, 2014 2:43 pm

 .
Len

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Re: AC-Adapter for Battery operated device

Post by haklesup » Thu May 22, 2014 4:16 pm

Unfortunately I need more data to go further. I'm left with nothing but to assume you did not make any mistakes along the way (but acknowledge you may have). Unless you post specific evidence, we are at a dead end with generic suggestions.

I think someone suggested putting a moderate sized cap across the external supply where you have it connected to the battery terminals. With a power button like that, the supply must already be on before you can activate it. Don't expect to switch the supply

Check that the intermediate battery terminals (between the cells) don't also sense a voltage to confirm insertion of for some other esoteric purpose. Such a truck could be causing the system to detect a fault and stay powered down. unlikely but worth checking off the list

Tell me more of the failed power board. were there any output wires besides just pos and neg, were there any digital control lines? what failed on it? there seems to be some undiscovered clues here.

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Re: AC-Adapter for Battery operated device

Post by dacflyer » Fri May 23, 2014 9:22 am

i was just gonna suggest also if it could possible be a intermediate (NOT INTERMITTENT) battery connection ( like a center tap )
Haklesup, beat me to it...

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Re: AC-Adapter for Battery operated device

Post by francesco » Tue May 27, 2014 6:48 am

The battery compartment only has 2 wires. Positive and negative. I believe if there was a problem with the intermediate battery connections the printer would not work properly when in use.

The DC power board only had 2 wires that came out of it.

DC power supply's voltage drops to 0 when connected to the battery terminals and need to figure out some kind of circuit I can make that will make it work. I don't see a cap working with this situation since a 17A power supply wouldn't work.

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Re: AC-Adapter for Battery operated device

Post by Lenp » Wed May 28, 2014 7:45 am

I said I was done but I feel compelled to respond!

Here's the unvarnished facts.
Battery products world wide are intended to be powered by ac power packs and they work, including the label printer you have.
If your power pack drops to 0 volts, you have a short circuit or a extreme load.
The '17 A' power supply has protection and it is shutting down.
If the printer works with batteries, and if this all happens when you connect a power supply, there is something wrong or different. PERIOD
francesco wrote:...need to figure out some kind of circuit I can make that will make it work
Stop trying to design a fix and get busy analyzing and troubleshooting the problem. It is evident that if there were no problem in your connections to the printer IT WOULD WORK.
You keep saying the same thing over and over without any real new or changed facts or findings and your facts presented and the results reported defy logic. I am not alone in that thinking

Tongue in cheek advise...
Try a much larger power supply and follow the smoke! :eek:
Len

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Re: AC-Adapter for Battery operated device

Post by francesco » Wed May 28, 2014 11:21 am

Lenp wrote: If your power pack drops to 0 volts, you have a short circuit or a extreme load.
If the printer works with batteries, and if this all happens when you connect a power supply, there is something wrong or different. PERIOD
If a device works fine with batteries, logically, it is in working condition and there is no short circuit or extreme load. Logically, if there was an extreme load, the batteries would drain very fast. Logically, if there was a short circuit, the printer would not turn on even with batteries. A short circuit can happen when the resistance of a circuit is too low and yes I have acknowledged from the beginning that there has to be a difference, hence the reason why Brother added a separate circuit for DC power supplies. The lower resistance design is probably there lower battery consumption. Logical.

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