[RE-wrenches] Trojan L-16s

Wed Jul 24 09:29:58 PDT 2013

Allen:

If you divide 20% (what's left to charge after bulk) by 50% (the average available absorb amps) it is .4  it's not the average.

By way of further explanation, I would suggest reading the Rolls/Surrette Battery User Manual Page 11 as it gives a pretty good explanation of "bulk" and "absorb" charge rates and calculations. The manual is consistent with the best practice  we have always used with batteries.

Over the years we have never had the problems that others have had with batteries. I am a firm believer that most of the battery problems that our industry experiences just stems from two basic causes;

1.     Multiple parallel strings. Which can be correctly dealt with, but usually is not

2.     Improper charge parameters. Undercharging i.e. low charge voltage and short absorb times.

Tom Duffy
Senior Solar Design Engineer
[Real-logo-X-195]
Toll Free 888-895-8179
tom at thesolar.biz<mailto:tom at thesolar.biz>
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From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
Sent: Tuesday, July 23, 2013 5:25 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Trojan L-16s

Tom,
Except that absorb starts off at 100% of the available amps, not 50%. Absorb starts as soon as bulk reaches the bulk voltage setpoint. It starts out at the same current as was available in bulk, then ramps back incrementally as the batteries continue to approach full, allowing only as much of the available current to flow to the batteries as is necessary to maintain the voltage setpoint plus loads.

On the finishing end, absorb doesn't have much to do with available amps. Rather, it either completes a timed cycle, with no particular control of the available amps except as regulated as above, or it switches to float when the amps necessary to maintain the bulk (a.k.a. absorption) voltage drops below a threshold, typically 2% of bank capacity.

And finally, the midpoint between 20 and 50 is 35, not 40.

Given that these principles form the basis of your definitive .42 figure, this number sounds pretty arbitrary. Is there anything more you can say by way of explanation?
Thanks, Allan
Allan Sindelar
Allan at positiveenergysolar.com<mailto:Allan at positiveenergysolar.com>
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc., a Certified B CorporationTM
3209 Richards Lane
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505 424-1112 office 780-2738 cell
www.positiveenergysolar.com<http://www.positiveenergysolar.com/>
On 7/23/2013 7:57 AM, Tom Duffy wrote:

Jay

Sorry I should have explained that too... Absorb starts off at around 50% of the available amps and tapers down to around 20% So I divided 20 by 50 = .40 there's a 5% loss factor hence .42

Tom Duffy

Senior Solar Design Engineer

Toll Free 888-895-8179

tom at thesolar.biz<mailto:tom at thesolar.biz>

Customer Service and Accounting 888-895-6810

Grid tie sales 888-895-7847

Off Grid sales 888-895-4058

Other Product Sales 888-895-9612

Central America Sales (Panama) 507-6-126-1253

Shipping and Receiving 888-895-6497

Tech Support 888-895-8179

SKYPE:  thesolarbiz

-----Original Message-----

From: re-wrenches-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at lists.re-wrenches.org> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jay Peltz

Sent: Monday, July 22, 2013 1:27 PM

To: RE-wrenches

Subject: Re: [RE-wrenches] Trojan L-16s

Hi Tom

Where did you get the .42 from?

Jay

Peltz power

Sent from my iPhone

On Jul 22, 2013, at 11:04 AM, Tom Duffy <Tom at thesolar.biz><mailto:Tom at thesolar.biz> wrote:

Drake

Keep the absorb rate recommended for the CC. The trimetric strays over

time and will become accurate again when you overcharge (equalize)

The math:

Amp hours of battery @ 20 hour rate divided by max charge available in

amps, from whatever you using to charge (solar or inverter/charger)

Times .42 = absorb time in hours

i.e. your system 980 watts,  980 divided by 28.8 (average volts) = 34

amps max charge

370 AH divided by 34 = 10.88 X .42 = 4.57 round up to 4.6 hours absorb

time for the CC Your inverter VFX3524 max charge 85 amps... 370

divided by 85 = 4.35 X .42 = 1.82 absorb time for the inverter/charger

when running generator

Tom Duffy

Senior Solar Design Engineer

Toll Free 888-895-8179

tom at thesolar.biz<mailto:tom at thesolar.biz>

Customer Service and Accounting 888-895-6810 Grid tie sales

888-895-7847 Off Grid sales 888-895-4058 Other Product Sales

888-895-9612 Central America Sales (Panama) 507-6-126-1253 Shipping

and Receiving 888-895-6497 Tech Support 888-895-8179

SKYPE:  thesolarbiz

-----Original Message-----

From: re-wrenches-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at lists.re-wrenches.org>

[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Drake

Sent: Monday, July 22, 2013 10:04 AM

To: RE-wrenches

Subject: Re: [RE-wrenches] Trojan L-16s

Hi Larry,

I will bump up the absorb voltage to 29.6 V. How long do you think the bank should stay in absorb at that rate?  The bank now seems healthy, with the bad battery replaced.  It does accept charge, without going high prematurely.  The max charge rate from the array is around C/10. The system can also be fast charged from a Honda 6500 inverter generator through the Outback 3524 VFX.

We have a Trimetric meter on the system. The discrepancy between the percent charge and the voltage is what demonstrated that we had a problem.

Thanks,

Drake

At 09:30 PM 7/19/2013, you wrote:

Hi Drake,

It always concerns me when I hear that a battery bank reaches absorb

setting very quickly. It typically means one of two things: very few

AH were removed from the bank; the battery bank has sulfated cells

due to chronic undercharging. Far too often I find the latter to be true.

Healthy batteries will accept current and hold the charge voltage

down with a fairly linear, slow climb to absorption voltage. Sulfated

batteries do not accept current well which allows voltage to climb

rapidly as the battery presents little load on the charging system.

I'm not sure how this plays into your original post about a bad cell

but it seemed worth mentioning.

My opinion is to aggressively charge, by using higher voltage, large

flooded batteries. This is especially true when the PV system is

moderate or undersized. 29.6 volts is what Trojan recommends. You can

go as high as 32 volts on the L-16's but make sure the temperature

compensation is installed properly and working. You will use more water.

One last comment, I highly recommend that ALL off grid systems have a

battery capacity monitor installed. It's kind of like flying an

airplane without a fuel gauge...it might not end in disaster.

Larry Crutcher

Starlight Solar Power Systems

On Jul 18, 2013, at 1:11 PM, Drake

<drake.chamberlin at redwoodalliance.org><mailto:drake.chamberlin at redwoodalliance.org> wrote:

Tom,

The batteries usually reach absorb voltage shortly after the sun hits

the array. The reason the bank wasn't working correctly is that one

cell was dead in one of the batteries.

I could increase the absorb time to 4.6 hours and the voltage to

29.6, especially since the bank has a new battery. That is longer and

higher than I'd previously heard recommended.

What would be the effect on water

consumption?  How did you calculate the absorb time?

Thanks,

Drake

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