Two bad OBCs at the same time

[Fairtax4me]

Not literally the same time, well maybe.
Over 4 years now I’ve been working on this fleet of carts, and with all the talk of bad OBCs, through 10 different electric carts of various years I have yet to have a failed OBC, until now.
I say now, but one probably failed sometime over the winter. The other one is kind of a maybe at this point.

Case number 1. Regen 2 cart with an older battery pack. It charges until the ammeter runs down to around 3 amps and it sits there for forever. And ever, and ever. I timed it at 22 hours yesterday, and it still hadn’t turned off. I have a spare OBC I can put in that one from another cart I junked a few years ago. I Think it worked then... maybe it still does. Also have another spare OBC that’s been in a box for forever. I have no idea what year or type of cart it came from. Never looked at it that close. Got options for that one.

Case number 2. This one has a strange symptom. Another regen 2 cart with a two year old set of Trojan 875s. This one charges for a while and eventually the ammeter shows all the way down to about a hair over 1 amp. And it stays there for quite a while before it finally turns off. It ran for about 14 hours the other day, which makes me think that it’s possibly a candidate for being considered “bad”. None of the other carts we have act like that (that I know of) when on the charger. I’ll re-test this one with a PD3 charger next week sometime to verify.
And before anyone asks batter connections are all clean and tight, and water levels in the cells are correct. I did not get a volt reading on the pack during charging. It does rest at 50.7 after sitting overnight, and all 6 batteries are within 2-3 hundreths of a volt of each other at rest.

I’m kinda leaning toward the second one being bad too. Any ideas?

[TahoeDawgZ71]

OBC failure is extremely rare, contrary to popular belief. The earlier OBCs from the late 90s to early 2000s that were beige in color were much more prone to failure than the new grey ones as you may have noticed.

Is the voltage reaching at least 58.3 during the charge cycle? If it's not reaching 58.3 it's never going to trigger a turn-off. Yes they should have timed out at 16 hours, but a lot of times on older OBCs that feature doesn't work as it's supposed to. Regardless, that doesn't render it "bad" if it can still charge your batteries and shut off once they're charged. The first step would be to make sure your batteries are reaching a high enough voltage to allow the OBC to consider them fully charged. For your notes, the correct replacement OBC for a regen 2 is now AM1229201. This is the new number for the old 101909902. If the OBC you have on your shelf has either one of these two numbers on it, it's compatible. The newer IQ OBCs will not work on a regen 2.

[Fairtax4me]

Thanks David, I'll give that a check. I can see that being an issue with the older pack.

[Sergio]

You may also want to check the suppression/flyback diode in the chargers used as they can cause the OBC FET in the "sense" wire to lock up if the diode has failed.

The OBC is designed with a "dead-zone" of around 2 amps, so it should never go below 3 amps if it is working properly.

[WalterM6]

Whenever that has happened to me it was a result of the Specific Gravity being off in one off the batteries. Below 1.300

[Fairtax4me]

You may also want to check the suppression/flyback diode in the chargers used as they can cause the OBC FET in the "sense" wire to lock up if the diode has failed.

The OBC is designed with a "dead-zone" of around 2 amps, so it should never go below 3 amps if it is working properly.

This is why I'm also testing with different chargers. Case number 1 has already been tested on both it's original PowerDrive, and a PD3 charger and acts the same with both.

Case 2 I will have to test again next week. I don't charge any cart on a Friday, because it something fails I don't want it plugged in all weekend long while I'm not around. I usually do not leave any cart plugged in overnight either, unless I can check on it every few hours.

Originally Posted by WalterM6

Whenever that has happened to me it was a result of the Specific Gravity being off in one off the batteries. Below 1.300

Is that a typo?
Specific gravity of a FLA cell should only be around 1.277 anyway, if the battery is fully charged. Most manufacturers specify around 1.265 as being good.
SG that is below about 1.200 after charging can be a problem.

I don't typically bother to test SG, because I have other faster methods of testing.
The older set may very well have low SG. There was a time when those batteries were getting water added from the well water tap. That was before I took over the maintenance of these carts.

[WalterM6]

It is the chargers that use the dv/dt algorithm that give trouble when the SG isn't right. Its been a long time since I've used a PD charger and I don't remember if they use it.