Voltage Drop After Watering

[virtualy]

I've had my 2008 PSD for a couple seasons now. It has done well in its intended mission - hauling materiel up a steepish hill.

I spun an axle a week or so ago. When I removed the wheels I found both rear axle castle nuts were very loose. The new hub cost me about $60. Lesson learned. While I was at it, I replaced the worn tire that the previous owner caused by running it low on air. And, since I was in maintenance mode, I watered all the batteries.

I used distilled water to top the batteries off, keeping the water level below or at the bottom of the fill tubes. I've noticed that the pack voltage has significantly diminished, dropping from a charged voltage of 38.4+ before the topping off to 38.0 now. I'm using the charger that came with the cart (Powerwise QE) and I know it's not a favorite of many of you. But that's an aside. Nothing has changed except the fully charged voltage drop.

Is this normal or cause for concern?

Thanks.

[caokgafamily]

Virtualy,

How much water did you have to add? Yes 38.0 is just under 100% So after you added the water you then charged it and it only reads 38.0? I always check my water after I charge it. I would just run it as normal and give it some time with some normal charging cycles then check it. I bet you it will be back up, I think you just have to give the new elecotrolyte? water some time.
Steve

[caokgafamily]

I could also not know what I'm talking about? Maybe some of the pro's will remark.
Steve

[JohnnieB]

The cell's voltage is tied to the Specific Gravity of the electrolyte (For Trojan batteries: SG + 0.845 = Cell voltage)

Adding water diluted the acid concentration in the electrolyte and lowered the SG, so the voltage decreased.

What you've seen happen, is normal and nothing to worry about. The voltage should return to normal the next time the batteries are charged.

BTW: 38.4V is a wee bit high, possibly due to the cells being low on water, which raised the SG. My guess is that the At-Rest voltage will be close to 38.2V after the next charge cycle.

FWIW: Even though my batteries are fully charge when I add water, I start a fresh charge cycle after I add water to them.

[virtualy]

Thanks for the reassurance. I'll go put a charge on it now.

BTW, is it important to have the batteries charged before adding water?

--P

[JohnnieB]

Originally Posted by virtualy

Thanks for the reassurance. I'll go put a charge on it now.

BTW, is it important to have the batteries charged before adding water?

--P

Yes, the electrolyte volume expands as the battery charges, both by heat gain and the migration of sulfate ions from the plates back into the electrolyte.

If water is added while the battery is partially discharged, the electrolyte volume might grow enough to overflow the cells, causing some of the acid component of the electrolyte to be lost, thereby weakening the battery. (Acid is never lost in the normal charge/discharge cycle, only water)

The only time water should be added to a partially discharged battery is if the plates are exposed to air, then only enough water should be added to cover the plates. Then charge the battery and fill to proper level after the charge is completed.

[virtualy]

Much obliged.