6v SLA

eluminator

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I think it's around 6.4 or 6.5 volts. It may depend on the charger and the battery construction.
 

SilverFox

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Hello Dave,

Lead Acid batteries are comfortable in the 1.75-2.3 volts per cell range (resting).

That works out to 5.25-6.9 volts for a 6 volt battery.

My Schulze information also gives 2.42 volts per cell for 3 hours. I am not exactly sure what that means, but would think that if you are using the battery to power your ICE charger at the field, you could charge it to 2.42 volts per cell and not do damage to the battery if you used it to recharge your pack within 3 hours.

2.42 volts per cell is more in line with what you automobile charging systems are set at. My charging system is set at 14.5 volts and the battery drops down to about 13 volts after shut down and resting for 30 minutes.

The Schulze information also mentions that if you run a battery down to 1.7 volts per cell, you will be doing damage to it.

Tom
 

Doug Owen

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SilverFox said:
Hello Dave,

Lead Acid batteries are comfortable in the 1.75-2.3 volts per cell range (resting).

<snip>

The Schulze information also mentions that if you run a battery down to 1.7 volts per cell, you will be doing damage to it.

Clearly we have a problem here. If the cell is "comfortable" at 1.75 Volts, and yet his 'having damage done to it' at 1.70 it's a lead pipe cinch that if you discharge a battery to 1.75 Volts per cell *average*, at least one cell in the string is in serious trouble. Wider margins are called for, don't discharge under say 2 Volts per cell average.

And remember, this voltage is *temperature dependant* what's safe when cold is not when hot. The numbers change -5 mV per cell per degree C (voltage goes down as temperature goes up).

Back to the original question, float voltage is typically 6.75 Volts, cycle charge voltage closer to seven.

Doug Owen
 

SilverFox

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Hello Doug,

Ah yes, the cell balancing issue...

The RC people have found that if you push a battery pack to (and beyond) its limits, the individual cells become imbalanced. However, using the pack well within its charge and discharge limits finds the cells staying very closely balanced. I have not seen test results for lead acid batteries, but this trend seems to hold for NiCd, NiMh, Li-Ion, and Li-Poly batteries.

The 1.75 volts per cell is listed as 100% fully discharged at 75 F. I have no idea where the Schulze people came up with their information on the damage at 1.7 volts per cell, but sometimes meanings are lost in the German to English translation. At any rate, discharging below 100% DOD always produces problems.

I agree that it is a lot safer to limit the discharge to 2.0 volts per cell.

Thank you for the reminder on the influence of temperature on voltage measurements on lead acid batteries. That detail had slipped my mind and the temperature effects can be significant.

Tom
 

James S

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I have a few 6v SLA's that I got from Allelectronics.com (direct link to item)

on the case it states that the cyclical charging voltage can be from 7.2 to 7.5 volts with an initial current of 0.84 amps.

I am charging this one from my bench supply even as we speak and at that voltage you do have to limit current or it will take much more initially.

They also print the float charge voltage on it, but I can't remember exactly and the battery is upstairs and I'm downstairs. If you need to know that I can go get it though :) In any case if you're not going to leave it on the charger and cook it you can charge to a slightly higher voltage than if you're going to leave it trickling all the time.

When this one comes off the charger in a few hours I'll take a measurement of the final no load voltage, but I'm sure it will sag back to normal as soon as you put any kind of load on it.
 
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