Battery Charger Experts........

I didn't want to hijack another thread.

I have about 5 battery chargers, and among them I have a large, 150 amp battery charger, one of the upright ones on wheels with a "crank" function. My wife gave it to me as a gift maybe 30 years ago. I'm not sure of the brand, without going back to my shop and looking.

Anyhoo, I've had a Dodge Grand Caravan sitting in my shop taking up space all winter. It's there mainly to be out of the way for snow removal. After I got back to my shop a couple of months ago after the debacle with my back, I tried the Dodge and the battery was dead. I put this charger on it for an hour or so and the Dodge fired right up. I tried it again after a week or so and it was dead again. This repeated several times. You wouldn't think a battery would go dead that soon.

The other day, I disconnected the battery ground post and put an amp meter between the battery and ground. It read a .02 amp draw, which would be consistent with maintaining the clock, radio stations, etc.

When I left the shop that day, the battery read 12.4 volts after being on the charger for a half hour, and with the ground cable disconnected. I checked it again this afternoon when I got to the shop and it read 11.8 volts.

I put a voltmeter on the battery charger and it was only putting out 10.6 volts. What the heck? How could the battery be charged to 12.4 volts when the charger was only putting out 10.6? The charger has always done what it was supposed to and this is the first time I ever put a volt meter on it.

I suspect the Dodge is perfectly innocent and the battery simply hasn't been getting a full charge. Before I left the shop this afternoon, I put a small 10 amp charger on it and am letting it set overnight. It was putting out 13 volts when I left. I'll see what it's done tomorrow.

It puzzles me that the big charger was only putting out 10.6 volts. I have a couple of 100 amp portable chargers, one in the garage at my house and the other in my other shop so I might play with one of them.

Something isn't quite adding up here.

Connect the "10.6 Volt" charger to a new/known good battery and try another voltage reading.

Battery chargers put out very "dirty" DC and, the battery under charge basically "filters" it.

I would say taking an "open circuit" DC voltage reading of an 'ol 150 Amp charger would be "meaningless".

I agree with Bob, chargers need to be charging to assess their charge voltage. I will also ad that a 12.4 voltage reading is not a charged battery. A good 12v battery should read 12.6 after 20 minutes of being disconnected from a full charge. One half hour is not enough time to charge a dead battery even at 30 amps or so charge rate. If you drove the van around for a couple of hours it should have been charged. If no driving was done, it will be fine tomorrow with the 10 amp charger on it. Jim

A.C. voltage read with a voltmeter is RMS voltage not peak to peak voltage. The battery charger is rectified to D.C. and is only 1/2 signwave so it's still RMS voltage not peak to peak. If the charger is connected to a good capacitor (the battery) then you achieve near peak to peak voltage ie 10.6 x 1.414 = 14.99 volts after the battery is charged.

Not sure about your charger but when the battery gets finicky like that and goes flat often then it’s usually the end of the line for it. I’d take a chance with a different charger for one last charge attempt but I suspect you’ll find the battery is the culprit.

You are right on your suspicion that the battery is not getting a full charge. After the charge you only have a surface charge on the battery. The best way to charge a lead acid battery is with what we used to refer to as a trickle charge. Those produce less than 2 amps and need to stay on for about 24 hours. Also I like to clean up the post and cable terminal, so I remove them if I don't know the condition of the connection. Remember bright and tight. I also believe Bob is correct.

As other have said, you will have a bit of a measurement error when you're trying to read the voltage of a disconnected battery charger. And that's going to be the case whether you have a typical "peak-averaging" meter or a high-end "true RMS" meter. That's because the output of most battery chargers is NOT DC! It's full-wave rectified AC (assuming both diodes are still good). What happens is the charger's diodes only conduct when the rectified sine wave voltage is greater than the battery voltage. As you increase the charge rate on the charger, it increases its output voltage which increases the duty cycle of the charge current.

Let's assume for a moment that the charger is adjusted to give a 10.6 volts RMS open-circuit voltage as you describe. 10.6 Vrms equals 15 volts peak (V_peak = V_rms x √2). So the battery will continue to charge at that setting until it reaches about 15 volts.

This is why it's not a good idea to leave a battery on a regular charger for an extended time, even on its lowest charge rate.

Would some one please explain the term R M S voltage?

The battery is damaged.
1. If a battery is ever fully discharged it damages the plates etc. and it will never hold the rated CCA.
Get yourself a Sola battery conductance tester. It will prove this statement.
2. Any battery, (ESP a diesel engine) should be replaced every 3 years. Regardless of how it operates currently.
new electronics in machines today require too much power and any battery over 3 years old can not provide proper voltage during cranking etc. that will cause all the sensors etc. to show errors etc.
Just FYI.
Jim

The battery has a three year free replacement. The three years is up this coming October, so if it's the battery, I'm home free.

> Would some one please explain the term R M S voltage?

RMS = "root mean square". It refers to a particular calculation made to determine the voltage of a waveform. The RMS voltage is essentially the DC equivalent to an AC voltage. If you apply an AC RMS voltage to a resistive load, it will generate the same heat as would the same DC voltage.

AC line voltages are normally given in RMS values. So "120 VAC" is really 120 Vrms which for a pure sine wave works out to 170 volts peak (340 volts peak-to-peak).

Cheap voltmeters typically don't measure "true" RMS but rather calculate it from the peak-to-peak voltage. That works fine for clean sine waves but can be way off for real-world waveforms. For example, for a square wave the RMS and peak voltages are identical. Inverters tend to generate non-sinusoidal waveforms and their outputs usually can't be accurately measured with a "peak-averaging" voltmeter.

Thanks for the responses. I'll digest all of it and play with it some more.

Anytime a modern vehicle is going to sit more that 2 weeks one battery cable should be disconnected. We leave our 15 Silverado truck sit in the garage for 3 1/2 months in the winter and I disconnect one cable. When we come home I charge it a little but it doesn't seem necessary, it starts right up. Any battery that sits any time discharged is junk!

If the garage isn't heated you should probably charge it once a month anyway. Batteries will self-discharge, even if disconnected. In MN a dead battery can freeze, ruining the battery and possibly making a mess if the case cracks.

Actually, I'm pretty sure the colder it is the slower they discharge! I leave 11 batteries over winter for 3 1/2 months and they're all OK!

A conductance battery tester will show you how many CCA's are in the battery. They are a very handy tool to have and the price has dropped a lot in the last few years.

Hello Goose,

If the battery was dead and it froze, chances are it is bad. Plates will expand when frozen and usually will increase the normal self discharging rate. 10 amps is TOO much to charge a battery that was that low.
You should charge the battery at the lowest setting that you have. 2 amps is good, and at that setting the battery will achieve the best saturation-charge.

Another way the a battery will self discharge is through the top. Take a voltage reading from the plus side anywhere on the top. Should not have any voltage readings.

2/10 of an amps seems a bit high,35 to 50 Ma is usually O.K. but I can't think of any drain that can draw that little?


Guido.

(quoted from post at 11:57:45 03/21/19) Hello Goose,

If the battery was dead and it froze, chances are it is bad. Plates will expand when frozen and usually will increase the normal self discharging rate. 10 amps is TOO much to charge a battery that was that low.
You should charge the battery at the lowest setting that you have. 2 amps is good, and at that setting the battery will achieve the best saturation-charge.

Another way the a battery will self discharge is through the top. Take a voltage reading from the plus side anywhere on the top. Should not have any voltage readings.

2/10 of an amps seems a bit high,35 to 50 Ma is usually O.K. but I can't think of any drain that can draw that little?


Guido.

Click to expand...

0.02 amp = 20 mA, which is about normal for keepalive radio/computer/etc.

I'll take issue with your point number 2. With regular use or with a good maintainer I plan on getting 10 years out of a battery even in our northern climate. Our most frequently used tractor has a 2002 date code battery in it that started it every couple of days all winter not plugged in. Thats unusual but 10 years is normal / fair to expect.

With batteries near 200$ for many of our tractors, and some needing 2, I'd be 1000$ a year in batteries on a 3 year schedule... Not gonna happen.

Alternators meant to maintain the charge in your battery. It will never completely charge it. All new battery's should be left on a trickle charger for a mimimum of 24 hours.

I agree, Bob.

I figured this out the first time I "repaired" one of the big multi-setting chargers. (which really wasn't broke)