best amperage for charging wet lead-acids?

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noobster
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best amperage for charging wet lead-acids?

What amperage would be best to charge a wet 12v 17ah battery in 3 hours if it was at 30% dod?
Thanks -Ryan

reikiman
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Re: best amperage for charging wet lead-acids?

Hm, 17 / 3 = 6.xxx so a 6 amp charger would do you. I don't know anything that would lead me to think a wet cell should charge at a slower rate than a sealed cell. And 6A is a reasonable rate to charge sealed cells.

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sparc5
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Re: best amperage for charging wet lead-acids?

The rule of thumb says 1/4 the AHr rating of the battery.
http://visforvoltage.org/forum/4320-how-trick-quotsmartquot-charger-that039s-not-so-smart

This might be above the charging time you'd like, I haven't done the math.

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dogman
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Re: best amperage for charging wet lead-acids?

Best for what? Slow is best for battery life, but I agree, 4-6 amps would be slow enough. Faster may cause you to have to add water more often though.

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sparc5
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Re: best amperage for charging wet lead-acids?

We charge slowly to keep the heat charging causes to buckle the plates. This make them prone to short circuiting. So to give the batteries the most years of use, I stick to that rule of thumb of 1/4 aH rating.

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Brock
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Re: best amperage for charging wet lead-acids?

In the renewable energy world the minimum is 5% of the battery capacity, below that and you won't mix up the electrolyte and 15% on the high side. I have heard 25% being thrown around, but most in the RE area agree that even at that rate you will shorten the life of the battery. Again these are charge rates used for larger RE battery bank systems that rarely go below 50% DOD as well.

Having said that if you only have 4 hours to charge, you only have 4 hours to charge, so you charge at the rate you can. I like to shoot somewhere between 5% and 10% if I can. My EVT charger charges at close to 30% and I have used it, but 95% of my charging is done at 2 amps or 6%.

Oh also the lower charge rates are more efficient as far as energy consumption is concerned. A faster charge rate will generate more heat (waste) as well.

spinningmagnets
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Re: best amperage for charging wet lead-acids?

I don't have an E-bike (yet!) I am doing my homework here before committing my "soon to be inflated" greenbacks.

I have many years of experience with automotive electrical systems, and have been reading recently about off-grid-home RE systems. Many of the components of an RE home are long-lasting, but the expensive battery packs must be occasionally replaced, so there is a very active discussion concerning how to get maximum life from the pack ($2000+ pack is not uncommon).

When overcharging on occasion (for equalizing) the extra amperage performs some electrolysis. This is when the water molecules (in wet cells) are separated into H2 and O2 and off-gasses through the cell vents. You must top-off with more water when this happens.

The chemical reaction that produces and then absorbs electrons is when the H2SO4 is split into H2 (which mostly stays in solution dissolved in the electrolyte, and the SO4 (sulfates) which coats the plates. The more the plates are coated, the less plate surface area is available for producing voltage, so volts go down.

If the sulfates aren't re-converted soon, they will begin crystallizing, and become hard to convert back. (keep wet cells charged-up soon).

One of the reasons that deep-discharging hurts this type of battery, is that while some amps are converting H2 (dissolved in solution) and SO4 back together, amps are also flowing through the plates, resulting in metal ionization erosion (like the ignition "points" on older cars).

Another way high charging rates hurt, is that the H2 and SO4's can only recombine at a certain rate, any additional amps above this rate will off-gas some of the soluable H2 that is waiting to recombine, leading to weak electrolyte.

One of the things that happens during an equalizing overcharge, is that weak electrolyte steals some H2 from the electrolyzing water to combine with the SO4's (excess O2's boil away), and some balance is restored (H2-to-SO4 ratio).

In an auto alternator, the voltage regulator feeds the battery just enough amps to re-combine the two (constantly assessing state-of-charge). As the battery gets closer to full charge, the amperage is constantly tapered off to "just enough".

Why don't E-bike battery chargers do this? If your batteries are $144/pack, and they last a year ($12/month), most people won't demand a smart charger that costs a few dollars more, low price is king for 90% of the market...

At least, this is what I "think" I've learned so far, please correct any part I may have mis-stated...

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