Charging SLA batteries

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1gr8bldr
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I have 14 8 amphr 12 volt batteries that I rotate each week to run 7 trail cameras. Each week, sometimes every other week, I rotate the charged batteries with the drained batteries and take those drained batteries home to begin a inconvient process of charging each one. I need to simplify. If possible, I would like to charge them all at once. Some of my batteries are new, some nearing 2 years old. Also, the charger must "float". It must also have an indicator for when it is finished. I also need some sort of tester that will tell me when they no longer perform. So, I need help with 2 things. What do I need? [1]Charger? [2]Tester? or a combination if there is such a thing.

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awilensky
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Re: Charging SLA batteries

Remote cameras out on the trail? These are begging for a tiny solar cell / charger - remarkably cost effective and you can get your life back.

1gr8bldr
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Re: Charging SLA batteries

awilensky wrote:

Remote cameras out on the trail? These are begging for a tiny solar cell / charger - remarkably cost effective and you can get your life back.

I have done this in the past where applicable but most are in heavely wooded areas.

Mik
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Re: Charging SLA batteries

I think you should be able to hook up all the batteries in parallel and charge them together. It will take much longer, of course, than charging a single battery, but you only need to hook it up once.

To connect them in parallel, connect all positive and all negative terminals together. The batteries must all be of similar state-of-charge (SOC), otherwise large currents and sparks could occur if you connect full and empty batteries together.

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1gr8bldr
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Re: Charging SLA batteries

Please recommend a charger and a tester

mf70
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Re: Charging SLA batteries

I second the parallel charging. The "needy" batteries will accept the charge, while the less depleted ones will have a higher internal resistance, and will hang back. As long as they all have the same chemistry, they'll all end up charged at the same time.

I've been happy with the Vector 2/6/10 charger. The line is now marketed by Black& Decker. Any modern Automotive charger will work. You don't even have to worry about getting a low enough rating to avoid overcharging the SLA's as you'll be hooking 14 up at a time.

For capacity testing, you'll have to do them individually, I'm afraid. I wrote up my method of capacity testing in this thread:

http://visforvoltage.org/forum/9723-instant-shelf-battery-capacity-measurement

It uses an inverter to get a consistent voltage cutoff, and the commonly available Kill-a-Watt meter to track power consumption.

Mark

mf70
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Re: Charging SLA batteries

I second the parallel charging. The "needy" batteries will accept the charge, while the less depleted ones will have a higher internal resistance, and will hang back. As long as they all have the same chemistry, they'll all end up charged at the same time.

I've been happy with the Vector 2/6/10 charger. The line is now marketed by Black& Decker. Any modern Automotive charger will work. You don't even have to worry about getting a low enough rating to avoid overcharging the SLA's as you'll be hooking 14 up at a time.

For capacity testing, you'll have to do them individually, I'm afraid. I wrote up my method of capacity testing in this thread:

http://visforvoltage.org/forum/9723-instant-shelf-battery-capacity-measurement

It uses an inverter to get a consistent voltage cutoff, and the commonly available Kill-a-Watt meter to track power consumption.

Mark

Mik
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Re: Charging SLA batteries

For testing you could just log how long the camera works, if that's possible. Can you check if the camera works when you swap the batteries?

You can detect really bad batteries by measuring their open voltage (= without a load) after they have been fully charged, then disconnected from each other and then left standing for a few hours. If one battery shows markedly lower voltage than the others, it is likely defective.

The most useful test is a capacity test under a load. You can use dedicated test equipment like a CBA3 or a 12V load, a DMM and a timer or stopwatch. Turn on the load, then measure the time it takes for the batteries voltage to drop to a cut-off level.

Regarding the charger choice: If you are happy with the results that your charger achieves with individual batteries, then you can probably just continue to use the same charger - just charge all batteries in parallel with it.

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mf70
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Re: Charging SLA batteries

A consistent cut-off level is critical, both for reliable capacity measurements and for protection of your batteries from over-discharging. Unless your cameras are specifically designed for SLA power, they probably will keep drawing current until it stops.

You can either hover over the batteries during discharge (boring- I've done it!) or have some low-voltage detection. The dedicated testing devices will do that, as will most off-the-shelf inverters. Likewise, you can either hover over the battery with the stopwatch and your fixed load (see above RE: boring) or set up some sort of automatic timing circuit, again either using the dedicated testing device or an off-the-shelf Kill-a-Watt power meter. The CBA3 looks like a good value, but it IS $150.00.

I second Mik's thought about the charger. It will be charging each battery at a lower rate, but that's a good thing if you have the time, reducing gassing from overcharge.

MF

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