Battery Numbers ?

JCJC · #1 01-01-2007

Taking a bit of time to discharge and equalise our batteries, question is I am putting 4.5Amps into them, they are taking an approx 50 min to charge (mixture of 3300's 3700's & 4200's), is there a way of working out AmpHour's that the battery is recieving?
Or would I have to do a discharge at say 30Amp to to get any meaningfull numbers.

Is there a way of telling when a set is going "off" by looking at charging/discharging numbers.

Thanks Mick

MattW · #2 01-01-2007

50mins charge at 4.5A would be 3750mAh going into them. However, in all honesty, the amount going in isn't really worth that much to you. It is what you can get out of them that really matters.

neiloliver · #3 01-01-2007

Mat is of course correct, its what you get out that is important, and capacity isnt everything, the running voltage is also important. You can buy a DVM for about £25 that hooks up to a PC and logs the DVM readings, If you have a constant current discharger you can log your discharge results and see the voltage (or do it manually in excel!) This is a good way of comparing batteries and seeing how flat the dischrage curve is under load. You will also see poor cells "dropping out" which results in little steps occuring in the discharge curve. Ideally all the cells should drop out together which is what gives you the sudden "dumping" effect where you car goes from Hero to Zero in half a lap...

N

JCJC · #4 01-01-2007

Thanks Guys,,,,,,But is there an sum I can use to get this figure, 3300's were under 50min, 3700's almost spot on 50min and our 4200's were doing 60min.

We have a Comp Electrics turbo35 and can out put to PC ! have to look into it.

Thanks again

neiloliver · #5 01-01-2007

If the charge time is 50 minutes and the charge current is 4.5A, then you do (50/60) x 4.5 = 3.75Ah input.

Is that what you wanted?

The most common question on this sort of thing is the numbers on the matched cells, for example 512 seconds at 30A

In such an example, if you wanted to know the discharge capacity then you divide the runtime in seconds by 3600 (the number of seconds in an hour) and multilpy the answer by the discharge rate (so 512/3600*30=4.26Ah).

ps - if anyones actually belives you can get 512 seconds from a 4200mAh cell at 30A then you are deluded...

JCJC · #6 01-01-2007

Thanks Neil, thats just what I wanted, even if it is just whimsie.....knew it had to be simple, just 50/60 the missing part for me. Thanks again

Hangon!! what do I have to do to add those nice square smilies........to this post?

MattW · #7 01-01-2007

JCJC, is it a std T35 or a GFX that you have??

I have a GFX, only had it a month or so and to be honest i haven't ever tried the output to PC feature - but it will give you all of the data you are ever likely to want when cycleing cells.

JCJC · #8 01-01-2007

Matt, its the standard T35, seems it is possible to connect to my PC but looks more work than I want to put in. Just spent more time than I expected discharging 8 packs, slaping them on an equaliser tray, and half charging so they can be stored till the end of the month when next we race, its a job that I can do "in the background" but have to keep half a mind on it while its being done. Thanks for the input tho, had this charger for a couple of years and seems to handle every thing I ask it. Its a bit big and has no back light but we have grown to love it.
Cheers Mick

JCJC · #9 08-01-2007

Found this on t'web http://www.csgnetwork.com/batterychgcalc.html
fun to play with........