Has anyone else seen this voltage problem?

Wiley · April 2011

Sometimes if I remove a load from my batteries, then reapply the same load, the battery voltage will increase by .4 or .5 volt.

This happens when the batteries are fully charged and I have a load on the system at sunset during the transition from power generation by the solar array to drawing totally from the batteries. The battery voltage will quickly drop to around 12 volts (and lower if I don't cycle the load). If I remove the load, and then reapply the same load, the resulting battery voltage will be about .5 volt higher than before and show a normal slow discharge rate from that point on.

The amperage draw through my household circuitry is the same before and after the load is cycled. Could this be a problem with my Xantrex charge controller? Or could it be a symptom of weakening batteries? Both the charge controller and batteries are about 5 years old.

RCinFLA · April 2011

Re: Has anyone else seen this voltage problem?

From a fully charged state, lead acid will exhibit an initial dip and recovery in voltage after load is applied. You don't have to take the load off and reapply, it will do it with a constant load.

Wiley · April 2011

Re: Has anyone else seen this voltage problem?

RCinFLA wrote: »

From a fully charged state, lead acid will exhibit an initial dip and recovery in voltage after load is applied. You don't have to take the load off and reapply, it will do it with a constant load.

In this case there is no recovery of voltage unless I take the load off. If I don't cycle the load the voltage continues to drop to 11 volts within a short period of time and with a load that should not cause such a drop. Only if I cycle the load will the voltage go back above 12 volts and then show a normal discharge rate for the load being carried. This is a new phenomenon that I've noticed only in the last few months and it doesn't happen all the time.

BB. · April 2011

Re: Has anyone else seen this voltage problem?

What is the AH and voltage of the battery bank?

What brand/ model of batteries?

What is the typical charging current you use?

Do you check specific gravity of the bank?

Use distilled water to refill the cells?

How deep of discharge do you typically take the bank?

Have you taken it to dead yet?

One person here said that he takes his batteries on a drive on the dirt roads in his area. The shaking of the drive helps his batteries.

-Bill

Wiley · April 2011

Re: Has anyone else seen this voltage problem?

I have four 6-volt 235 Ah deep cycle batteries from Interstate Batteries, connected in series and parallel for a 12 volt bank.

Typical charging amperage is around 10 to 15, with a maximum of 22.

I check specific gravity periodically, and all cells read healthy and nearly the same, with no noticeably weaker cells. I always use distilled water.

It's rare to discharge the bank more than about 15% and I equalize about once a month. I doubt the batteries have ever been below a 50% charge, certainly never close to dead.

The intermittent nature of this problem makes me wonder if, when it occurs, there's a draw on the batteries which doesn't register on the ammeter that shows the draw of the household circuitry, maybe running back through the Xantrex C35 controller toward the array, even though diodes are supposed to prevent that. But if that was the case, why would removing the load stop the problem?, unless maybe the voltage boost from the batteries when the load is removed trips something in the circuitry which prevents that backflow? I don't know enough about how these things are constructed to know whether that's possible. The only time I've noticed this problem is when I have a load on the system late in the day as the array output decreases and the batteries gradually take on the full load.

RCinFLA · April 2011

Re: Has anyone else seen this voltage problem?

Maybe grid oxidation or excess lead dioxide build up on positive plates. This happens on batteries that have not had much discharge and constant float charging.

Sometimes a heavy discharge (25% AH rating) for about 30 minutes will help.

You are probably equalizing a bit too often. Every two or three months should suffice.

A friend of mine had Interstate golf cart batteries that were left on float charge for almost two years continously with no discharge. When he loaded them they collapsed with high internal resistance. They had positive grid corrosion. They improved a little with some quick discharge/recharge attempts but still too much internal resistance to be useful.

BB. · April 2011

Re: Has anyone else seen this voltage problem?

You are on the minimum size for recommended charging current... Typically, we recommend 5% to 13% as a good range with ~10% being a good number for tall flooded cell batteries to properly mix the electrolyte (as with any rule of thumb, there are arguments that recommend different numbers--but these seem to get most people going well--and different batteries are designed for different uses--so their min/max may be different):

470 AH * 0.05 = 23.5 amps minimum recommended
470 AH * 0.10 = 47.0 amps nominal recommended
470 AH * 0.13 = 61.1 amps rough maximum cost effective for solar panels

So--For your batteries there are a few different options to consider:

Batteries are near end of life for typical "inexpensive" battery bank
Batteries can be helped with some deeper cycling--Lead Acid batteries actually like cycling for longer life.
Stratification of battery electrolyte has damaged plates (bottom of battery with dense electrolyte--top with less dense/more water).

I really have no idea--#1 is certainly likely. #2--probably not as you are cycling them. And #3 does not sound likely if all your cells are well balanced and S.G. is reading normal for fully charged batteries.

If you have a DC current clamp meter (cheap functional meter here), you could measure each string under load and confirm that both are properly sharing charging/discharging current....

It is not unusual for one battery to "go bad" before the others... Measuring current per string and voltage on each battery (make sure no battery is really high or really load Charging/Discharging/Resting). If you find one battery acting differently than the rest--it may be causing your bank to not charge/discharge correctly.

I cannot understand why making a load, then resting, then making a load again--causes the battery bank to behave differently (better). I would not have expected it (--I am no expert).

Checking with a Volt meter for bad cable connections (set meter to 2 volt or 200 mV full scale and check each cable/connection for low/equal voltage drop when under full load or charging--Any spot that has more drop than any other may be a loose connection or failing cable).

My 2 cents worth of guesses.

-Bill

Adding to what RC says--Many times you can find positive grid corrosion by looking closely at the Positive Battery Post--Look for the post "extruding" from the battery being pushed up by the grid/plate corrosion.

Paul54 · April 2011

Re: Has anyone else seen this voltage problem?

When you say at sunset, are your panels and charge controller still putting out some power? If the anomaly you are seeing occurs around twilight, might it be something kicking in with the charge controller? Does it ever occur after dark when panels and controller are truly shut down?

Wiley · April 2011

Re: Has anyone else seen this voltage problem?

I only see this problem at night after all output from the array has ceased, but when there has been a continuous current draw on the system during the time when the panels have gone from some output to no output. My thought was that maybe something in the charge controller isn't handling that transition as it should and is allowing the controller to draw power from the batteries. But, being ignorant of just how these things work, I have no idea whether that's possible.

Thanks for everyone's input. I'll check my battery posts for any signs of corrosion and get a current clamp meter to see whether there is more draw from the batteries than is showing on the house current meter. But it wouldn't surprise me if it's just aging batteries that turn out to be the cause of the problem.

petertearai · May 2011

Re: Has anyone else seen this voltage problem?

I would be looking for a loose connection. If you have a very quiet location listen for an ark noise .

simmtron · May 2011

Re: Has anyone else seen this voltage problem?

My Heliotrope's HPV-22 has a similiar problem , the display in the evening will show say 12.05 volts when a meter on the batteries will show 12.6 volts, there is a switch on the controller to change between voltage and amps, when I move the swich to amps and back to volts it fixes the problem. Do you have a digital meter on the controller?

Wiley · May 2011

Re: Has anyone else seen this voltage problem?

My charge controller doesn't have a meter. I just have an analog ammeter wired into the system in such a way as to show the current draw of the house circuitry. If current is flowing back to and through the controller from the batteries, it wouldn't show up on my ammeter.

BB. · May 2011

Re: Has anyone else seen this voltage problem?

Meters have inacuracies--But that sounds like a large one. Which meter is accurate?

Are you saying your charge controller changes from 12.05 to 12.60 volts just moving a switch back and forth (like the contacts are dirty?). Or do you believe the batteries are actually changing voltage because you switched some function of the charge controller (i.e., is the separate meter reading the same voltage before and after?).

Also, it does not hurt to check connections to see if they are tight and clean. I like to, with the wiring under load (or under charging), set my DMM to 2.0 volts or 200 mVolts full scale and measure the voltage drop across each connection and length of wire... Sometimes, you will find very low or zero volt drops until you hit one wire or connection that is higher resistance. Cleaning connections (or replacing a corroded cable) will usually be required to get everything back working again.

-Bill

BB. · May 2011

Re: Has anyone else seen this voltage problem?

Generally a charge controller is not going to leak very much current back at night--even if it is failing.

If you have a serious fault that is causing batteries to quickly deplete--you should be seeing lots of smoke or smelling/feeling something hot (i.e., significant current flow should cause significant heating).

-Bill

Blackcherry04 · May 2011

Re: Has anyone else seen this voltage problem?

I think what your seeing is the cycle of life from a set of dying batteries. No expert, but what you are seeing is the same thing I see over and over with 6 V GC batteries. The symptoms already have been mentioned, bulging case, positive post pushing up out of the case.

How I notice mine is my inverter acts like a UPS when switching from shore power to generator. As it comes off float (13.2) after a week or more, it will drop to 12.2 on pickup of the load. Once, I'd think that maybe the refrigerator had short cycled or was in a defrost cycle and was pulling on it, I'd turn it off or ( blame my wife about having 600 w light bar on in the bathroom ) . I have a hydraulic truster system on the boat, so I go back onto generator power until I am out of the Marina then back to the Inverter. So, then back to inverter power (1,000 ah battery bank). When the inverter picks back up the voltage will be around 12.5 or more.

I'd think " cable corrosion " and pull all the cables and clean them and have the same issues.

After cutting open one of the batteries and seeing what they looked like I got my answer, Sulfation and Corrosion of the plates. You'll also notice they'll stop using as much water, that is a symptom of whats going on inside, It will grow to the point that the hydrogen gas cannot escape will collect under the plates and begin to displace the electrolyte until it flows out of the vent caps in the last stage. You can also hear them, instead of a gassing sound, it becomes almost a moan from the stresses inside. ( lol.... I am not nuts, but you can tell I have had some close contact with my batteries. )

Other factors with the electrolyte have to be going on also. When you replace the batteries, it all goes away for 4-5 years and you start the clock over.

Wiley · May 2011

Re: Has anyone else seen this voltage problem?

I'm coming to the conclusion that my 5-year old batteries are nearing the end-of-life stage. There don't seem to be any visible signs of sulfation, but I have noticed they don't require the addition of as much water as they used to.

Has anyone had experience with battery desulfators? A lot of solar energy stores sell Battery Life Savers Desulfators. I've found some reviews and comments from people who say these desulfators really do work, but I'm not totally convinced yet that it's worth buying one.

mike95490 · May 2011

Re: Has anyone else seen this voltage problem?

Aside from the 10 or 15 watts they consume, they dont hurt anything from what I've heard. I have one, but I can't say it made my batteries like new. After a year, (used batteries, in workshop) they still aren't dead.

Blackcherry04 · May 2011

Re: Has anyone else seen this voltage problem?

I use my batteries really hard. While I try not to go under the 50% DOD, it's hard to say exactly how many 50% discharges they go through in 5 years, maybe 400-600 times. 10 batteries cost about $800 or $160 a year. I have a 20 KW generator that costs $8.00 a hour at least to run, not really counting maintenance and replacement. The $160 a year makes them a bargain, expendable and just a cost of having fun. Some weekends they will be bulk charged 3-5 times and then absorbed charged late on Sunday.

I see others that have batteries that sit on a float charge for months at a time that don't last any longer then mine, if as long. My theory is use them or lose them.

niel · May 2011

Re: Has anyone else seen this voltage problem?

you are right to a point as my batteries like it when i cycle them a bit and you don't have to go as deeply as 50%. cycling deeply and more often can be bad too and lessen the useful life of the batteries.

Photowhit · May 2011

Re: Has anyone else seen this voltage problem?

For what it's worth, I believe my batteries have used more water as they have aged. I also think this is the norm.

niel · May 2011

Re: Has anyone else seen this voltage problem?

Photowhit wrote: »

For what it's worth, I believe my batteries have used more water as they have aged. I also think this is the norm.

i will agree with that as when things get older they don't always work as expected and the older they get the farther from the norm it goes. me included.

:p

westbranch · May 2011

Re: Has anyone else seen this voltage problem?

I was told by a Pro in the maintenance field for "BIG" AGM installations that the dip is called (something like) Koo- du- Why (phonetic spelling) a french term for the dip-and-recovery you observed. I have searched but unsuccessfully for more info on the term... It is a sign of failing batteries due to sulphation and, in AGMs, positive plate oxidation where the O2 bonds onto the positive plates rather than recombining with the Hydrogen. An end stage of the battery identified as 'bulging' of the battery case.

HTH
Eric

BB. · May 2011

Re: Has anyone else seen this voltage problem?

Old post from Crewzer/Jim,

crewzer wrote: »

...

This sounds normal to me. Battery voltage always drops when a loads is applied. Usually, the voltage recovers a bit as the electrolyte begins to self-mix. This behavior is referred to as a “coup de fouet”, or crack of the whip.

Batteries produce electricity as the result of a chemical reaction, and, like all chemical reactions, battery behavior is affected by temperature. The electrolyte in cold batteries tend to be a bit sluggish, and the self-mixing is slower. As a result, the under-load voltage drop is more pronounced than under nominal conditions (i.e., 77 F, or 25 C).

HTH,
Jim / crewzer

Blackcherry04 · May 2011

Re: Has anyone else seen this voltage problem?

It all makes sense to me. I've tried a lot of different things with 10 batteries paralleled in a 12 v DC bank, there just so many things you can do. The voltage drop thing usually starts to show up sometime in the 3-4 year on my bank, the beginning of the end.

I equalize regularly, water once a month or more in hot weather. I am not a wasteful guy, but again, $160 a year is the cost of doing business. The gas going through my generator @ $8.00 a hour becomes a big consideration.

I thought about building a Distributive Charging system, like the EV car guys use. I don't know if the ROI is worth the time and money.

westbranch · May 2011

Re: Has anyone else seen this voltage problem?

thanks for finding that Bill. Don't remember ever reading that from Crewzer.. google here I come..

Has anyone else seen this voltage problem?

Comments

Categories