Univolt/Battery Help

[wingfoot321]

Instrument panel indicated low charge on my batteries.

One battery was down on water. Refilled it and put it on a charger for a good charge. Low battery will only test 9 volts now on my battery tester.

Other battery was ok on water and tests at 12+ volts on the tester.

Univolt tests 13.5+ volts hooked up to the good battery.

Ques. (1) Is univolt overcharging and boiling out the water? Thought univolts were suppose to taper charge?
(2) Why is only one battery low on water?
(3) Can I use the weak battery until it gets worse?

Batteries are 3 years old or very close. I have been leaving batteries hooked up when I am in Texas and hooked up to 120volts for 3 months during winter.

[azflycaster]

It sounds like the one battery (9 volt) has an internal short and is history. To answer your questions.

1. Yes, the univolt is boiling the batteries. Univolts do not have 3 stage charging like the better replacements do.
2. You are lucky only one is bad
3. No, a battery reading 9 volts needs to be replaced. The short will most likely pull the other one down also.

[RUSSELL]

Hi there,
I bet your univolt also hums at 60 cycle rate. My 1985 univolt cost me 4 bateries. I replaced the univolt with a battery charger rated at 20 amps. It has sensors that shut the charging down when the batt is at 13.5 v. It also has a trikle charge. Unles you have a lot of stuff running of 12 volts 20 amp charger is good enough to keep the batterys up. This unit cost me about 65 dollars. There are better units bit all at 350 + price range

Regards Russ in Tucson

[FrenchBern]

Wingfoot 321, You need to tell us what model Univolt you have. The Univolt in my 1970 Overlander has a series voltage regulater which normally regulates the voltage to 13.5 volts and can't overcharge batteries. A few weeks ago I looked at a 1965 Univolt that was totally different and did Hum. The output voltage was 13.8 volts and is always powering the AS and keeping the battery up without any problem per the owner.
Contrary to many opinions, the properly working Univolts does regulate the voltage and in your case my first guess is the 9 volt battery has an internal shorted cell. If it is not a sealed battery, check the voltage between each cells individually. They should be the same (1/6 of the total voltage). You can do this simply by placing the probe in each successive electrolyte without touching the plates.
If you removed a shorted cell battery (which is in parallel with another battery) which was absorbing all the current, the other battery will now be overcharging IF the Univolt is not regulating and will follow the same faith.
You mentioned the univolt voltage at 13.5+ volts. Was it measured with a meter or an oscilloscope? For instance my old Univolt read 13.8 volts on any analog or digital meters but because it has an open rectifier and a shorted series regulator it has half wave spikes of 18 volts (loaded voltage) and will silently boil a battery in a few days.
I will be glad to dilute this comment if it is too thick,

[Pick]

Has anyone experimented with putting a big filter capacitor at the output of the Univolt? Like the kind they put on high end mobile stereo installations?

[Zeppelinium]

Originally Posted by wingfoot321

...One battery was down on water. Refilled it and put it on a charger for a good charge. Low battery will only test 9 volts now on my battery tester.

Other battery was ok on water and tests at 12+ volts on the tester.

...(3) Can I use the weak battery until it gets worse?

Batteries are 3 years old or very close. I have been leaving batteries hooked up when I am in Texas and hooked up to 120volts for 3 months during winter.

Yes, 9 volt battery is dead.

You can parallel a new and old battery, but it's like flying a two-engine airplane. The second engine only puts the crash site further away. Seriously, the interaction of charging currents and internal resistance makes it imperative that paralleled batteries have the same usage history, or the old battery will ruin the new one relatively quickly (months, not years). So always buy two together.

If you leave them hooked up, you have to check the water often, more often in warm weather. You will develop a history of water usage to modify how often you need to check and refill.

[wingfoot321]

Stilling going through battery, univolt system. Next question thankyou.

I checked the univolt's charging voltage a little closer today. Looking at the front of the trailer, the right side battery is receiving 13.95volts and the left side battery is receiving 13.5 volts at the same time.

It was the rightside battery receiving 13.95 volts that was down on water and the leftside receiving 13.5 was just fine on water. Didn't have time to loosen connectors, etc. to see if the 13.5 volt side would come up.

Do those voltages sound like I have trouble with my univolt. It is 19 years old and maybe it is time?

Appreciate any comments.

[SilverToy]

Hello all -

Also going through the battery/ Univolt system check right now.

Question: Is there a competant and econmical system to keep tabs on battery charge and relative health of this key system??? Have seen TriMatic? systems (bestconverter.com) but they run $200 or better.

Is the old 'Plug In' amp meter just as good or better???

Got a "Charge Wizard" for the IP9100/40A and it is blinking away as advertised.... Is there another way???

Thanks in advance for any and all replies!

Axel

[Zeppelinium]

Originally Posted by SilverToy

...Question: Is there a competant and econmical system to keep tabs on battery charge and relative health of this key system??? Have seen TriMatic? systems (bestconverter.com) but they run $200 or better. ...

Axel,

Battery health is one of the toughest technological issues, even for lead-acid batteries that have been around practically forever. In order to get a true handle it, you need to be able to independently check each battery under load--which requires a relay for each battery--and make comparisons between load and no-load voltage. You also would need to track charging and discharging Amp-hours. There are various strategies to simplify this, but in the end, a real battery condition monitor is expensive. If you have one battery, you can get pretty close with a monitor that runs over several charge/discharge cycles, but with parallel batteries the monitor has to make lots of assumptions.

The best practical solution is to use something like the Charge Wizard coupled with an accurate voltmeter. Get some experience looking at the voltage (converter off--you just want battery output) under no load when the batteries are charged and compare that to the voltage as you put a load on, or several loads. You'll get a feel for estimating battery condition much faster than you think.

Wingfoot,

If your 19 year old Univolt is like my 30 year old Univolt, you've got more than a problem with the Univolt. (My following comment is based on the assumption that your Univolt has only one charging output and that it is paralleled to both batteries.) First, you've got either a too-small wire guage going to one or both batteries or you've got a small but significant resistance at one connection, maybe corrosion or somethings loose, etc. You just can't have two paralleled batteries with 0.4 volts difference. Second, in addition to this random small resistance, you may have substantially differing currents between your batteries. This would indicate that one has a higher internal impedence (battery is going or is already "bad") and you not only have current going out to supply your lights, etc., but one battery is actually feeding the other one.

If you've got #8 wire between both batteries and the Univolt (#10 will suffice if you wire runs are just a few feet and total load is under 25 Amps), then I'd start checking for loose crimps or corroded connectors.

[Zeppelinium]

Oops, I really should have included an Ammeter in the second paragraph above. For charging, the Ammeter is essential. On discharge, the voltmeter can tell you most of what you need to know, given you know approximately what load you're putting on the battery.

Kudos to Over59 for providing this link:

http://www.amplepower.com/primer/full/index.html

[lewster]

Originally Posted by Pick

Has anyone experimented with putting a big filter capacitor at the output of the Univolt? Like the kind they put on high end mobile stereo installations?

Pick,

That is supposed to be the function of the batteries on the old style converters. They were to function as DC filters so you would not be putting full ripple DC from the converter output directly into your lights and other DC uses. In this case, a cap won't do anything that the batteries won't.

[Cracker]

Are the newer converters, i.e., "Univolt?", any better than the old units? If so, when did Airstream make a change? So far I haven't experienced any significant problems with respect to battery maintenance - aside from the problems I personally created!