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Russco charger malfunction (again)

6249 Views 14 Replies 6 Participants Last post by  DLK
Hi all

My 3-year old russco 24-120 charger seems to be acting up again.

Last time it was a blown bridge rectifier. That was an easy and cheap fix fortunately.

This time the symptoms are a bit different:

The charger is working, but if you turn the current adjustment knob all the way up (as I normally have it set), the charging current jumps to about 14-15 amps (normally with my 126V battery it would be about 11 amps) and the output current is unstable, it oscillates and causes the needle on the current gauge to bounce around, and the charger makes some funny noises (bumping and popping sounds) while doing it. (It's not the fan, which is working fine). Eventually, the output fuse will blow if I let it continue like this.

For now I have turned the current adjustment knob down and this seems to be allowing the charger to behave itself, but I would like to know what is going on.

I don't know if it is related or not but this behavior started after some particularly cold (for around here, anyway) days. (15-20 degrees farenheit) The charger is located inside the cabin of the car so it is well protected from the elements so I would not expect moisture intrusion to be at fault.

Clearly whatever regulates output current has developed an issue; possibly it is just an internal adjustment that has (suddenly) gone out of whack. Any ideas?
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Well, no one else has replied to your question, so I'll give it a try.

I know a little about Russco chargers. :D

So you're charging a 126 volt pack?

Are you aware your SC24-120 charger is for charging 132 and 144 packs ONLY? Read your manual.

Operating this charger into a 126 volt pack will over-current the charger. Your 11 amp output verifies this.

No wonder you're having problems! The charger has been mis-applied. :eek:

You can't blame the charger for that. :(
Huh. Well I dug out my manual, and on page one, the specifications say:

Voltage, output: 100-212 VDC (adjustable)
and a few lines down...
Amperage, output 12.5 Max Amps (adjustable)

And the sticker right on the front of the charger says:

Voltage: 80 - 200VDC
Max amps: 15

(a little grainy, but readable here) :

The only specific mention of 132 and 144 volt charging in my manual has to do with setting up the boost transformer. (which I determined by trial and error is also necessary with 126V). It is worth noting that there are some significant discrepancies in the manual vs. my actual charger (specifically, the timed shutoff is completely different in my charger compared to what the manual describes, and of course the differences in output specifications between the manual and the charger as seen above)

I am guessing that perhaps the specification maybe have changed since I got my charger, or I got a transitional unit in-between designs, maybe unintentionally. The only other explanation is that I got the wrong manual (with the right cover page) and also the wrong stickers got applied to the charger, and I doubt the latter more than the former.

Given this, any further ideas? Failing that, diagnostic steps? Not interested in fixing blame, only fixing problems :)

In the meantime I'll keep the current turned down.

thanks for your replies.
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OK, well my confusion is well founded it seems. Yes, the introduction does say 132 and 144, I probably ignored that given the other specs in the book and the label on charger itself which suggest a much wider voltage range is fine, as has already been pointed out. So I will concede that I am apparently abusing the charger. I would humbly suggest however some clarification to the manual and labeling and some added emphasis to the voltage range requirements.

So back to fixing it. Right now I can't find a serial number on the charger. It is in a recessed location in the car behind the driver's seat (plenty of ventilation though; I made sure of that) and I can't find the number. That will have to wait until I pull the charger. This may not be for a while since it IS working and I have other stuff to attend to. So I'd like to just gather some more information at this point. Since it is out of warantee anyway, I would like to fix it myself if possible (I am not new to fixing electrical equipment) but I am humble enough to know when something is over my head and at that point I would be willing to send it in. So In the meantime, if it is a given that this charger is misapplied for a 126V pack, and it is also a given that I don't really want to replace the charger, a couple questions:

1) realistically, is a 6V difference (less than 5% overall relative to the 132V minimum) in nominal pack voltage really enough to cause the charger to have problems? (bearing in mind that for about the first 6 months my car was running I used this charger (without the boost transformer) to charge a 102V pack with no problems at all, before I added 24V of additional batteries to get to my current battery configuration)

2) if the answer to 1) is yes, then would keeping the current setting turned down to something below the maximum mitigate any further issues with the charger owing to the lower voltage battery?

3) what about this charger makes it limited to 132 to 144V nominal battery voltage? I'm sure the LC filter and the igbt/mosfet/whatever that throttles the current can handle a slightly lower battery voltage than that as long as the current is kept to a manageable level. What component(s) are operating out of spec here? Maybe it just is a bit out of its peak efficiency range?

More random info: My settings with the 126V battery have always been a voltage knob setting of about 75 to 80 depending on the ambient temperature (warmer == lower number) and I have always had the current knob set to its maximum except for times when I was charging off of a 15A circuit or using a long extension cord (most of the last 6 months actually, I recently moved and I did not get a good charging outlet installed until only a few weeks ago). I've never popped a 20A mains breaker with the charger unless something else big was plugged into the same circuit and the charger's own 20A pop-out breaker has never popped except for when it had the bridge rectifier failure. As for overcurrent on the output side, I have popped the 15A output fuse once or twice due to my own stupidity, but in normal usage it has never blown until this most recent issue started occuring.

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Thank you for the explanation. I fully understand basic electrical concepts and I would not intentionally use the wrong tool for the job. We have already gone over why I ended up misapplying the charger. I am just trying to diagnose what is actually wrong at this point and determine what I can do to avoid issues in the future.

Given that the SC24 is a SC18 with a bigger input side, I am not sure why a slightly lower boost voltage might not be another option in my case though, based on your description. I was going to ask that but it sounds like you think that won't work. To me anyway, it sounds like its all about keeping the current under control and that would do it.

You didn't answer whether or not you thought turning down the output current would mitigate this problem. Or put another way, What is the maximum sustainable output current for an SC18 or SC24?

Define FWB please. I am assuming that is the control board.

I will post to this thread again if and when I figure out what the issue is.

Thanks again.
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The fuse holder is fine. I did have a recurring fuse holder issue elsewhere in the charging circuit (not part of the charger) but I recently have changed to a bigger form factor of fuse.

I really don't think anything is wrong with the current handling components of the charger (LC filter, bridge rectifier and current limiting silicon (mosfet, or whatever it uses, I haven't dug that deeply into it) despite the previous suggestions from Russco. I base this on the facts that

1) It works fine with the current knob set low. So whatever actually switches the current is working.

2) The current ramp-down and shutoff timer are working.

My own theory is that whatever measures output currrent to limit it when the current knob is maxed out is at fault. If the charger uses a hall effect device to measure current, it may have failed. I had such a failure occur in a welder I have with similar behavior (unstable, too-high current) Without having yet disassembled the charger to actually look at how the control board works, I am only speculating however.

Another theory that was posited to me out-of-band from this forum thread was that the current knob potentiometer was noisy or making poor contact. This came from another person with a russco charger who has experienced this. I don't think its the problem in my case though.

I probably won't take anything apart anytime soon since I can put up with charging at a somewhat lower rate. If and when I do identify the problem I will post again to say what it was.
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