# How do I safely monitor my 96v battery pack?



## Guest (Jun 29, 2011)

....how fast do you plan on driving? That will make a huge difference in your mileage but you won't go far even at lower speeds. I say to always build your distance needs at 55 mph so if you go slower you go further. If you build a pack that will do 50 miles at 35 mph you may only get 30 miles at 55 mph. Maybe. Best I got was 16 6 volt batteries with lead and got at best 25 miles at 55 and that was taking the pack to a crawl. That is reality. So don't expect super long distances. If you need great distances you need to go with lithium and even then you need a bunch. Oh, don't forget you will need a full wallet too.


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## madderscience (Jun 28, 2008)

You should invest in a KWH counter such as a packtracker or one of the other gauges available from the various EV stores. this will be by far the most accurate indicator of your available energy. You will still have to calibrate it to your batteries and car (basically, drive til you can tell it is getting weak, and look at the meter. However much power you have used at that point is the usable capacity of the pack).

With twelve 8V golf cart batteries (800lbs of lead or so) in a rabbit I would agree with Gottdi's assessment of usable range. You will probably have about 6 to 7 KwH usable capacity. 

During charging, I would expect the batteries should get to about 10.5V each (2.6V per cell or so), when full, and should be held there for about 30 minutes before the charger shuts off in order to equalize the pack. Any charger that is designed for a 96V lead pack should do this for you by ramping back current once the pack voltage reaches the proper level for your pack. Some chargers are calibrated from the factory and some need to be calibrated by you. refer to the instructions from the one you have.

During driving, You don't want the battery voltage to sag too much. As the batteries discharge, the same load will cause greater sag. In your case, you should try to keep the battery voltage under load at or greater than about 72V or about 1.5v per cell. If you are to the point where pulling less than about 100A from the pack drops your voltage to this level, you are pretty much done. It would be even better if you could watch each battery individually and stop when the weakest battery hits about 6V under that same amp load. A BMS can do this for you, or in your case with only 12 batteries it is reasonably practical to just buy some digital panel meters from ebay and put one on each battery and mount all the meters somewhere where you can see them while driving. 

Cheers


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## dtbaker (Jan 5, 2008)

Gas Free said:


> I have completed my EV and have ordered a charger. How do I monitor my 96v battery pack (12 x 8v batteries). At full charge, should it read 104v or 108v or something else? At what discharging voltage reading do I start damaging the batteries? 96v, 94v?
> With 12 x 8v (65lb) batteries in a VW Rabbit, how much range should I truthfully expect?
> Thanks
> Tom in Sarasota Fl.


with lead batteries, the voltage drop is very predictable from 'full' to 'empty', and the state-of-charge meters are really just voltmeters calibrated to the nominal pack voltage. you do NOT need individual monitors on flooded-lead batteries, they essentially 'balance' each time you bring them up to 'gassing' voltage at end of charge. You DO need to make sure you keep them properly watered for best life.

if these 8v batteries are golf cart flooded leads, you'll probably get around 35 or maybe 40 mile MAX range under good conditions while batteries are new.... then they'll start dropping capacity pretty fast after 5k or 6k miles... probably down to 50% of original after 8k miles.

if you happen to still need an instrumentation pod, I have a nice pillar mount set with voltmeter, ammeter, and 96v SOC meter all ready to bolt in left over from my upgrade to 120v of lithium.... available at discount from retail cost of gauges and all pre-wired. see post in classifieds:

http://www.diyelectriccar.com/forums/showthread.php/fs-3-gauge-pillar-mount-pod-53968.html

I also have a central watering system for sale (flow-rite) since I have moved to lithium.... a big time saver for watering floodies!

http://www.diyelectriccar.com/forums/showthread.php/flow-rite-pro-fill-watering-system-53964.html


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