C/5 - C/30 ? [RE-wrenches]

[Dan Rice]

Drake, Bob-O & other battery veterans,

Two questions. When you refer to a charge rate of, say, C/5, is it correct
to assume that "C" refers to the amp-hour capacity of the battery at the 20
hour discharge rate? Which would mean that, for a single string of Trojan
T-105's with a 20 hour rate stated capacity of 225 AH, C/5 would be 45 AH,
and a C/5 charge rate would be 45 amps for this string? If that's the case,
what is your experience with such a high charge rate? Bob-O, your
observation that this charge rate is applicable to heavily discharged
batteries makes sense, as does your comment that the charge rate must be
tapered once the battery reaches 50-60% capacity. What I am wondering is,
can such a charge rate be maintained beyond 60% SOC plus or minus in any
case, or does charging voltage continue to rise beyond a reasonable (safe)
level? If a battery is not cycled below 50% DoD, is it even possible to
maintain a C/5 for more than a couple of minutes without the battery voltage
rising beyond a desirable level?

I'd love to hear all 12 opinions...

Dan Rice
Abundant Sun, LLC.

----- Original Message -----
From: "Bob-O Schultze, Electron Connection" <econnect at snowcrest.net>
To: <RE-wrenches at topica.com>
Sent: Wednesday, October 04, 2006 7:53 AM
Subject: Re: C/5 - C/30 ? [RE-wrenches]


|
| Drake,
| I don't think it hurts to charge T105 or L16 types at a C/5 rate IF
| they are heavily discharged. However, you must reduce that rate once
| they get much over 50-60% SOC again. In fact, you are unlikely to hit
| a 100% SOC with that rate regardless. Think about filling a 5 gallon
| bucket with a high volume, high pressure hose. You can never get it
| full unless you reduce the flow.
| As to equalizing very often, I used to be a big fan of that as it was
| easy for me to do 6-8 months out of the year with hydro. My attitude
| was that I'll take an EQ charge whenever I can get it. After living
| with many sets of L16s over the years, I've changed my tune on that.
| My regime of regulating at a higher voltage seemed to wear out a set
| of batts just as fast as habitually undercharging them. I've come to
| realize that thinking was a holdover form the old days of slam-bang
| regulation. Since the advent of PWM, it just isn't necessary and
| perhaps even harmful. Live and learn. How often one EQs depends more
| on how the batts are charged and discharged. If you are cycling
| fairly deeply- say 50%- on a regular basis, then I think fairly often
| EQs are a good thing. If you are getting the batts full pretty much
| every day with your RE sources and not discharging more than 15-20%,
| It is far less necessary and can be done a couple of times a year.
| Just my opinion. Bet if you get 10 Wrenches in a room talking about
| this you'll get 12 opinions.
| Cheers, bob-O
| On Oct 4, 2006, at 5:57 AM, Drake Chamberlin wrote:
|
| >
| >
| > Should we be charging L-16s and golf cart batteries at higher rates
| > than previously recommended.  The owner of a photovoltaic house I
| > used to live in ramped his L-16 bank up to 30 volts each night.
| > The bank was old and stiff, but he seemed to get good results.  The
| > bank was being charged at around C/9.
| >
| > So the question is, "does the fast charge rate apply only to heavy
| > duty industrial batteries, or does it also apply L-16s and
| > T-105s?"  Also, should we bring the batteries to equalize level
| > voltages for short times, on a weekly basis?
| >
| > Thanks,
| >
| > Drake


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