Idle 48v pack of B&B + powercheq goes south

[Roy]

After about 5 months over winter, my 48v pack basically died. Seeking to understand
what happened. Here are the details
I ran my 48v bike kit for about 10 months with power cheqs.
then I had mechanical problems and parked it for 3 months.
Got it going again for another 2 months. Finally
the batteries are down to 5 miles range (from 20) so I parked it
(November) and decided to upgrade to 60v. This meant
another 5 months of non-use (due to controller mods &
winter storms) but the original 48v pack with powercheqs
was left plugged continuously into a Soniel smart charger.
Soneil is a "smart" charger that according to the manufacturer
can be left plugged in continously

Anyhow, a few days ago when I went to test the modified
controller - surprise NO power and only extremely low
voltage output. Dis-assembling connections I find that
only the first battery in the string has proper voltage. The
other three are effectively dead and perhaps have been
so for months. No blown fuses anywhere, no
funny lights on the chargers or PQs. The string was
just in some sort of death sleep :*(

I wonder how this happened. It's not a great
loss as the bats were due for swapping out anyway. The
bats were 12v12ah B&B's AGM types. So I went
un-awares from 4 presumably balanced but weak
batteries to 1 "good" battery and 3 dead ones.

Can forum folks offer any insight?

1. If a single battery in a string goes bad is there any
risk of powercheqs propagating the problem to the
other batteries?

2. How can I test the 3 powercheqs before installing
them on the new batteries?

3. Did I goof just leaving the string plugged in? What would
have been smarter?

4. What's the recommended way of preserving a 4 bat
string when it's idle for several months?


Thanks for any info you can offer.

Roy in Santa Clara
26April 2008

 

[kbarrett]

Powercheqs are a discharge style SLA balancer, correct?

You may have killed your SLAs by using up their recharge cycles by having the powercheqs endlessly balance them while the Soniel provides juice for this circus.

I would suggest not having a discharge style balancer attached to a battery in storage.

Best storage solution for SLA ( in my opinion ) is to take them out every few months, put a load on them, use up a few amp-hours, and then fully charge ( use the powercheqs then if you want ). Then disassemble and store for a few more months.

As for now: Maybe try a 12v desulfinator on each individual cell, and see if they are resurectable?

 

[PJD]

My understanding, based on using them for a few years now, is that Powercheqs "shuttle" charge. One is used for each pair of batteries and each unit discharges the higher battery and charges the low one . I have had no trouble storing my 40AH packs with powercheqs on them. I simply top-off charge every couple weeks through the winter. They also have a small quiescent drain, but it is not significant unless you neglect the pack entirely.

I think keeping your SLA's plugged into the chargers for multi-months periods may not have been good idea.

 

[D-Man]

Yeah, I don't really know how powercheq's operate exactly. I remember you said you had 1000 miles at one time but range was down. Since the powercheq's didn't really extend the miles or perform a miracle, I wouldn't put them back on if you get new batteries. Also, if you get new batts, you might want to get the B.B. EVP series. Its good for 300 complete cycles at 1C. The stock BP series is only 180 at .25C. Not really too good for running 48 volt on a tandem. I do have them but they came stock with my go-hub. My range is down too. I want to get the better batts next time. I don't really like leaving a charger on when I'm not watching because things like that can happen. I have some "marine" batteries that I check once a month and trickle charge them for like half a day. This is suppose to be the benefit of having sla's. Long term storage and not much charging needed. If you stay with the 48 volt charger, just make sure the new batts are all equal and fully charged before hooking it up. Probably the reason you bought powercheq's.

 

[fechter]

As far as I know, the PowerCheq will try to equalize two batteries regardless of voltage. If one battery shorted, it could have pulled the others down.

As far as storage goes, I prefer to leave my SLA's disconnected during storage, and charge them every month or so for a day, then disconnect them again. I have some that are nearly 10 years old that still perform well.

I'm not sure how you are supposed to test a PowerCheq other than look at the lights and measure the voltage on each battery. If you put a small load on one battery (light bulb), you should see the voltage on the other battery track the one with a load.

 

[andrew]

The stock BP series is only 180 at .25C.

Where did you get that information?

To me it sounds like the charger slowly killed the batteries. Trickle charging batteries should be done with temperature compensation because it needs to be pretty close. That's why it is probably better to leave the batteries off the charger, and charge them once every month or so. AGMs can be stored for long periods due to a low self-discharge rate. The Powercheq Quiescent Current Draw is listed as 5 ma, so thats 3.6 ah per month. I would charge the batteries once every two weeks if the powercheqs are left connected.

I would try adding a small amount of water to each cell. Start with 1/2 ml per cell of distilled water. You'll need a dropper to measure this precisely. Then, charge the batteries for a long while, maybe even a few days. This might help bring them back, or at least restore some capacity. I would definitely leave the powercheqs in! I don't think it's anything the powercheqs did. You might also check all of the fuses in them, and verify that they are working properly.

 

[D-Man]

The stock BP series is only 180 at .25C.

Where did you get that information?

.

From the B.B technical handbook ( based on full cycles). See this thread:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=296&st=0&sk=t&sd=a&start=30

 

[safe]

Finally the batteries are down to 5 miles range (from 20) so I parked it (November) and decided to upgrade to 60v.

Which means that your batteries were already collectively down to 25%, but (as you've said) three of them are in really bad shape and one is barely surviving.

I've got a similiar situation on my bike where one cell is completely gone and the other two have the ability to hold some charge, but it's unknown how much more they have left in them. (after 3,200 miles)

Your balancer might have contributed some to the decline, but time is the big killer... time and temperature. (and depth of discharge)

Lead Acid batteries are cheap, but they only are designed to last for a few years under the best of ebike design situations. If you are using a "C" rate higher than 1C in your power system then you will be accellerating the decay rate.

Sometimes things just get old... as the saying goes:

"You can't escape death or taxes."

...or SLA batteries losing their capacity.

Just buy some more. (they're cheap)

 

[D-Man]

Lead Acid batteries are cheap, but they only are designed to last for a few years under the best of ebike design situations. If you are using a "C" rate higher than 1C in your power system then you will be accellerating the decay rate.

If the batteries are not tested/rated for 1C then all you will get is the minimum amount of cycles if your lucky. Half cyles or quarter cycles won't do much good if they were only rated and tested at .25C. Also if you left your charger on with totally dead batteries and didn't know about it, wouldn't that wreck the charger or blow a fuse?

 

[Roy]

Thanks to all folks who answered my query. Seems the bottom line is that
"old" AGM's are like old people - they can die pretty suddenly for many reasons
that are hard to determine.

I am planning to still use the powercheqs on my next string and will
see what happens.