Measuring Battery Charge ?
 

Hi
I bought a used electric bike and it has2 MK (ES 12-12) brand Sealed
Lead Acid batteries, they are rated at 12 volts and 12 Ah
--- http://www.mkbattery.com
I'm trying to figure out how to measure how much capacity they
have after the charger light ---- signals they are fully charged.

I can't afford to buy an expensive load tester.

It appears, that if I wire 6 (#1157) 12 volt automotive bulbs together
and then use a Watts Up meter --- it may tell me the percent of charge
in the batteries (A few websites rate these bulbs at 2.1 amps each)

Is it possible to determine with reasonable accuracy the percentage of
charge that the battery has in it ?

Am I on the right track ? Is there a better way ?

Thanks for any information that you can offer.

Thanks --- Joe
PS
I have a spare battery pack to carry with me --- but have the same issue
with it --- how can I verify that it's holding enough charge ?
My concern is heading out on the bike and running out of power a
half mile from home ---- as I (am sorry to say) that I am handicapped and
can't walk it home. I'm trying avoid a potential problem.

1. Have you checked for dirty and/or lose wiring connections?

2. How old are your battery packs?

3. Are your brakes releasing properly and do the wheels spin freely?

If the battery packs are new and fully charged (see "Note ***" below) then I'd next check for poor or lose wiring connections. Otherwise, you may have a bad motor, motor controller, battery management system (BMS), or some other power system problem (i.e. system short, bad throttle, etc, etc).

If the connections are good; I'd next suspect that your batteries are not be holding a charge. This common problem is is often the result of old and/or "worn-out" batteries (to many "discharge/charge cycles"), or from accidentally allowing the batteries to discharge too far and/or remain discharged for too long. You should always fully charge you batteries (as per your ebike and/or battery manufacturer's instructions) about 1/2 to 1 hour after each and every use (it's a good idea to allow the battery or batteries to cool-off before you charge them).

As you probably realize, one of the best ways to test a battery's ability to hold a charge is with a load tester (~ $25 at Harbor Freight). You will need to test the batteries separately (disconnected) if you're using a HF or similar12 volt load tester.

Otherwise, you should be able to measure the unloaded voltage of your batteries with your Watts Up meter. Otherwise you can use a 10-20 dollar digital volt meter. Your Watts Up meter should also allow you to monitor the power system voltage drop during use.

Note ***: generally speaking, a 12 volt lead acid battery will be fully (100%) charged when it reaches a peak of 12.65 volts. Thus, 2x 12 volt batteries should indicate a full charge when they reach 25.3 volts (while connected in series). A 50% rate of charge will be somewhere in the range of 12.25v iirc. Again, always consult and/or follow your ebike and/or battery manufacturer's charging, use, and storage instructions.

Here's a link with some in-depth info on troubleshooting ebikes and scooters:

http://www.electric-bikes.com/bikes/diag-03.html

First, Thank you for the reply. Greatly appreciated !


The chap, I bought it from purchased it last May (2012).
He said that he rode it 3 or 4 times and then parked it,
until I bought it last month. Decided it wasn't his thing.


Anyway, the connectors and cables are like new ----
what concened me was --- according to him --- he
didn't have a trickle charger on the batteries and couldn't
remember the last time the batteries were charged.


I was concerned that the batteries may have problem,
so I took them over to a local shopthat sells electric
wheelchairs.


Their service technican checked them with a volt meter
and said it read 12+ volts, but he decided to put them
on their load tester --- he said they both tested very
weak and it was probably from sitting uncharged for
an extended period.


So, I bought a desulphator (www.wizbangplus.com/)
and have had on the batteries for the last 3 weeks.


I going back to the wheelchair shop --- one more time
to see if the desulfator worked? (Don't want to wear
out my welcome).


So, it appears the next step is to get a volt meter and
possibly 2 new batteries.


Thanks again, for your assitance


Joe

You're more than welcome jkinvt.

I vaguely a remember hearing of one, or more, battery "desulfator" type products back when I was an auto mechanic during the '80s and early '90s.

Unfortunately, I can't remember if these products worked or not...

Anyway, good luck with your electric bike, and let us know how it turns out!

Most reliable measure of how far you can go with a particular bike/motor/battery combination is to just ride with it until the battery starts getting weak. Since you have a spare battery pack I'd suggest going for rides where you never get far enough away from home to be a problem getting back using that spare pack. Keep track of how far you go each time and pretty soon you should have a good feel for a dependable range.

SLA batteries intended for electric bicycle use should be of the deep-discharge type and are reasonably tolerant to being discharged to 50% or even further. As indicated at:
http://batteryuniversity.com/learn/a...ased_batteries
they should be able to handle about 400 charge cycles when taken down to 50% as compared to about 1000 if only taken down to 70%. So while it's best to recharge frequently, it's not that bad to run them down further for a few test cycles in order to get a good feel for the range you can safely depend on having.

Should be deep discharge batteries, for this application... Like marine batteries for electric motors or golf cart batteries...