# How do I know when to stop charging?

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no3rdseat
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How do I know when to stop charging?

Hi all-

This question pertains to a string charger on an e-Fun D but could apply to AGM battery theory in general.

In an attempt to keep from cooking any batteries that might have lagging neighbors, I put my string charger on a timer at work. I can check the individual battery voltages to see what the level of charge is. So I'm trying to figure out exactly how long to keep the charger turned on. Today as my bike was charging after two hours, it read 14.1 volts with a DVM. I turned off the charger and each battery read 13.7 volts. Over the course of about a minute, they all settled down to about 13.65 or so. I suspect as they sit they will settle down some more in time during the course of the day.

My understanding is that the charger will pulse 14v and then measure the actual battery voltage, then pulse, then measure, etc.

My question is, what is the voltage that I should bring them up to and is there another criteria to measure to know if they are close to fully charged?

Thanks
Rick Stewart

andrew
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Re: How do I know when to stop charging?

Volt SOC
12.66 100%
12.45 75%
12.24 50%
12.06 25%
11.89 0%

I found this chart on the web here.

As Dave mentioned, it's open circuit voltage. Perhaps a clearer way to say
it would be "resting". Resting typically means no charging or discharging
for at least 3 hours and is even more accurate if you wait until overnight
to compare your battery's voltage to this chart.

A more advanced way to determine full charge for a battery in cycle use is to charge it at a constant voltage of 14.5-14.7v at room temperature and when the current tapers to <.01CA than the battery is fully charged. For a 35 ah battery this would be .35 amps.

I'd suggest you use individual 12v chargers for each battery. I'm going to mount 6 Vector 1087CBD chargers on my bike and can make them much smaller by taking most of the plastic housing off leaving just the orange part and the display.

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

no3rdseat
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Re: How do I know when to stop charging?

Thanks Andrew. I have a bank charger at home that I use to fill my batteries at night. I use the string charger on a timer at work to top them up enough to get home (ala USATRACY). I'm trying to figure out exactly how long to leave the timer on without cooking the batteries. My e-Fun has 5-50aH B&B batteries. USATRACY said two hours on the string charger after riding 15 miles should do the trick. I'm just trying to figure out an accurate way to calculate the time required as I don't know what the aH rating of my Kingpan KP-A string charger is.

Rick

reikiman
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Re: How do I know when to stop charging?

The amount of time to charge depends on the amount of discharge. However you asked how do you know when to stop charging, and that is best determined by the voltage. So long as your charger is properly designed it will detect the voltage and shut down at the appropriate time.

The B&B Technical Manual has a lot of information about charging -- http://www.bb-battery.com/techmanual.asp

The only real danger with using a pack charger is if the battery pack is unbalanced. If so, it may happen that one of the batteries goes into the danger zone (above 15v). I'd expect that by bank charging at night your pack will remain relatively balanced during the day.

FWIW amp-hours is not an appropriate measure for a charger. Amp-hours is a measure of amps over time. Chargers are rated in Amps, being the max amps they can deliver.

One way you can watch the charging process is with this: Compact Digital Battery Analyzer for Any 4-60V Rechargeable Battery Pack up to 50Amp It shows you the instantaneous volts/amps as well as cumulative amp-hours. Hurm, but it's rated for 60v max and the battery pack you're looking at will be close to 70v when fully charged. Hurm. Hurm. That really is a useful meter, you just connect it inline with the charger or controller and you can monitor current/voltage while charging or riding. But I've never used it on a 60v system, only 48v and less.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

antiscab
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Re: How do I know when to stop charging?

Ive owned both the compact battery analyzer and the cycle analyst. to be honest get the cycle analyst, it has a remote shunt so you can mount the display on the dash instead of having to put it in an obscure place near the batteries. alternatively you could get a paktrakr.

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

no3rdseat
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Re: How do I know when to stop charging?

FWIW amp-hours is not an appropriate measure for a charger. Amp-hours is a measure of amps over time. Chargers are rated in Amps, being the max amps they can deliver.

You sir are correct... I had amp hours on the brain. Thanks for the correction. :)

no3rdseat
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Re: How do I know when to stop charging?

to be honest get the cycle analyst, it has a remote shunt

mmmm... remote shunt...[drool]

mf70
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Re: How do I know when to stop charging?

I got the WattsUp, and removed the shunt. I'll mount the shunt near the controller and take the three sense wires to the handlebars. The MFR's website has a (buried) page on how to do this.

http://www.rc-electronics-usa.com/special-mods.html

About the original Q, if you're doing opportunity charging, I'd recommend recharging to 80% SOC. That will get you home, but keep you away from overcharging any of the batteries. SLA's are easy to cook.

Mark

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