Determining capacity of off-brand batteries

Tulumtam · June 2012

A potential client has some batteries that I have not encountered before, Trace T-115. (http://www.traceinternational.com/productos/baterias.htm)

The website says that these are 225 amp hour batteries. The label on the batteries confirms this. The problem is that the installer that sold the batteries to the client claims that they are 450 amp hour batteries, which he says is obvious from the shape and size (they look like an L-16). The system is sized and the inverter programmed as if they are 450 amp hour batteries. The batteries are only 6 weeks old, so the client doesn't want to replace them immediately. The system has numerous design and installation problems, and the client wants to turn the system over to me for a redesign.

I tend to believe the label and website over the installer, but the client still believes the installer. Is there a way to test the capacity of the batteries to know and/or demonstrate to the client the actual capacity? It is a functioning off-grid hotel, so we can't shut them down for too long to run experiments. Any suggestions hugely appreciated! I want to sort this out before deciding whether I will accept the challenge of making this system function!

westbranch · June 2012

Re: Determining capacity of off-brand batteries

The manufacturer should have load testing tables that you can use to compare the batteries to. IIRC you apply a known load (~C/5 or C/10) and measure & record the Voltage of the batteries at fixed time intervals , in this case probably every 10 minutes, to confirm the load is sustainable and not seriously affecting the future overall health of the battery, ie taking the battery down below 50% SoC.
Make sense?
the discharge table will be for a set end Voltage per cell/battery so be careful to choose a higher V one, a some are for very deep discharge...

HTH

Cariboocoot · June 2012

Re: Determining capacity of off-brand batteries

It is not easy to determine the capacity of batteries. If you can't take them out of service it's impossible. The usual test is to charge them, measure Voltage and specific gravity at rest, then discharge them at a controlled rate and remeasure.

As far as I know the T-115 is 225 Amp hours like it says (T-115 is a case designation). Two in parallel would be 450 Amp hours.

If there is any meter keeping track of the power usage you can do a rough calculation from that and see how it compares to the SG reading difference before and after use. Less than perfect, but it certainly would indicate the difference of a factor of 2.

Sounds like the system was set up entirely wrong and the client is dissatisfied with the result. If they are not having the original installer correct the error and are giving the job to you then they should trust what you say about it, including the battery size.

BB. · June 2012

Re: Determining capacity of off-brand batteries

You can weigh a battery too... A 6 volt 220 AH battery--Somewhere around 67 lbs or so... A 450 AH 6v battery around 113 lbs (using Trojan specs).

Also, make sure you measure the voltage across the battery... There are 4 volt and 2 volt batteries too. For example, Trojan has a 2 volt / 3 cell battery (the cells actually connected in parallel internally--3 watering holes and all):

L16RE-B

6v

375ah

11.575"
7.125"
17.7"
118lbs

L16RE-2V

2v

1110ah

11.575"
7.125"
17.7"
119lbs

You will get a higher AH rating at the lower cell voltage (same Watt*Hours of storage either way).

-Bill

Determining capacity of off-brand batteries

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