Li-Ion 36V trouble. Battery or Charger?

[henning]

Hi,

I have a 36V EV Tech LiPo battery. When I received that battery ~6
months ago, during the first days it would only charged up to 40.2V or
so with the tiny EV Tech 3Amp charger. That slowly got better during
the first few weeks of daily usage, so that after ~6 weeks or so the
freshly charged battery showed between 41.5 and 41.8V, and was capable
of delivering great power for sufficient time. With my PowerpackMotors
35Amp controller I did not have any cutout since several months, with
6 to 12 miles rides per day.

Now, since two weeks, this ~6-month old battery suddenly does not
charge well. After a full charging cycle of 7hrs charging from an
almost empty battery, the battery only has between 39.5 and 40.4V, and
clearly is not fully charged, producing 33V low-voltage cutouts at
hills even when freshly charged. I have the impression that the
charger goes directly into a trickle charging mode, and the battery is
charged only very slowly. 24hrs of charging eventually brings the
voltage at the battery to 40.8V. But it is not comparable to the 41.5
to 41.8V that I had until two weeks ago.

I suspect the charger. Could that be?
That charger has two tiny potentiometers behind the silver cover, that
might allow adjusting the chargers behavior. But I don't think that I
should touch these, after having read this here:
http://www.powerstream.com/li.htm

Doug, any suggestions? I am writing to the group because I assume the
warranty is over for my charger.
Can anybody recommend a good charger? Or, is this the charger, or
could the battery have a bad cell?

Henning.

[Richard Papa]

It sounds like one cell out of whack so try not to fully discharge the pack
until you know for sure.

One thing I read on some older Li-Po packs (Not EV Tech!) was they had to
open the pack and charge the cell that was not fully charged. It could be
two? So if you can do this safely (I could not) then that's an idea.

I'm sure Doug will know what to do and hope you get it fixed soon. Doubt
it's the charger but who knows?

Take care & please keep us posted,

Rich

[Joe]

henning,
i'd try giving DC a call first thing.
keep in mind spring is a very busy time for bike sales and service.

[Nimbuzz]

H, Yes call Doug. Are using the charger intended for the battery? My
EV Tech chargers are black plastic and have no potentiometers.
Al

[henning]

Hi,
Yes, I use the correct charger, the one Doug sent with the pack. A
very nice one. If you peel the label off the charger a quarter inch,
you will find two tiny holes that lead to potentiometers, I believe.

Henning.

[plasmadust]

Henning,
We have had a few problems with the BMS wires getting loose inside the
battery.
What you can do for the time being is charge the battery directly
through the main leads. See if this pumps the volts back up. This will
tell us if it is the BMS.
You can not over charge the battery with that charger. We have tested
the cells at 3X cell voltage for 72 hours and nothing happened, so
putting 42V across the pack will charge it if the cells are good. We
haven't seen any bad cells yet, but there is always a first.
DC

[henning]

Thanks, Doug, for the suggestion.
In the mean time, the battery works perfectly again. Today it was
charged to 41.8V. So, it really looks like a bad contact somewhere,
because a cell could not go chemically bad and then suddenly work
again.
Despite all your suggestions, I still suspect the charger. I had
dropped it really hard onto the concrete floor in the garage some time
ago, and it might well have taken a crack somewhere. The red LED, for
example, is broken now, but the charger still works, at least this
morning.

I will keep an eye on this, and monitor the voltage that the charger
puts out. If the problem re-occurs, I will also try to charge the
battery directly without going through the BMS, as you suggested,
Doug.

For the moment, it looks as usual: Powerful super battery and motor,
and quick and helpful comment from Doug at EV Tech. And I will track
the charger's behavior.

Henning.

[Steve Mooring]

All batteries, even the lipos, have their lifespan. I have had one of
Doug's 36v 15ah batteries for a long, long time. And it has taken a lot
of punishment. No doubling up on batteries, like Larry does for Uma.
I used it for a couple of thousand miles of commuting, then my son has
had it on his bike for a while, and then finally it has been moved to
the ignoble role of scooter juicer! So, I don't know for sure how many
charge cycles it has had. Many, certainly 500 or more. Also, every
time it is used, it is used to LVCO and beyond by my kids. So, I went
out and checked the fully charged voltage tonight. My instrument gave
me 40.4 volts. The charger goes to 42 volts (and it is a new charger).
A 1.6 volt drop is, after all that, not too bad, but it makes a
surprising difference in performance.

So, this tells me that the lithium iron phosphate solution will be
superior on multiple levels. Time to charge, # of cycles, sturdy under
abuse, and hopefully, cost. Lipoly was and is a big step up, but it has
already been surpassed.

Steve

-----Original Message-----
From: Tidal...@googlegroups.com [mailto:Tidal...@googlegroups.com]
On Behalf Of henning
Sent: Tuesday, April 17, 2007 8:50 PM
To: TidalForce Forum

[Don Harmon]

Hi Steve,

Just got some more info. on the LiFePo4's. The Charge time on the packs is
2 Hrs. and the Warranty will be 2 years.

[Don Harmon]

I agree with you Steve. The only thing holding Life Batteries down right
now is the price. They
are not quite competetitive with Lipoly Batteries, but this is about to
change rather quickly. With
the testing we have done - they show superior qualities to Lipoly. In fact,
I believe the warranty
will be 2 years. I am not sure what Doug's warranty is ?

Best,

Don

----- Original Message -----
From: "Steve Mooring" <st...@mooringnet.com>
To: <Tidal...@googlegroups.com>

[henning]

Just another update:
Charger and battery are fine since several days again. 41.9V at the
beginning of my ride today, full power for a very long ride at top
speed. This battery is awsome. My guess is that I had a bad contact
somewhere in my charger, that now disappeared, for the time being.
Henning.

[deerfencer1]

Great to hear that Henning!

I've had a similar thing going on with my packs for a while now, where
they don't seem to charge above 40.4V or so no matter what I do, then
out of the blue one day they'll charge up close to 42V--or at least
one of them will. I have yet to figure it out, but riding the double
pack I usually have plenty of juice for my normal rides (1/2 hour to
an hour in turbo X mode).

I will say in all honesty that I think I have lost some capacity since
I bought them 11 months ago--perhaps 10-15%--but as Steve posted, all
batteries eventually wear out, and I'll be pleased as punch if I get
another full season or two out of them.

$400-500/year may sound like a pricey habit, but compared to many
other hobbies/passions (think boats, motorcycles, cars), it's chump
change IMO, and a small price to pay for the silent and awesome power.
These lipos seem like a perfect match for the Wavecrest motors, and
truly propel them into a new performance level over the stock NIMHs.
(Matra take note!)

Larry

[henning]

Hm... Or could it be that these batteries need to be heavily used in
order to stay "awake", and as soon as you don't use them for a week or
so, they fall back to a "sleepy" mode, until you put them to regular
usage again?