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Old 08-05-2010, 05:44 PM   #1
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Too High Battery Voltage?

I plugged the trailer in after charging my batteries and confirming that they will charge completely with my battery charger and hold that charge. I was worried they might be bad but decided they are okay for our upcoming trip ( http://www.airforums.com/forums/f449...why-67735.html ).

Now I notice that the trailer charged the batteries up to 16.5v measured at the batteries. Funny thing is that the power panel indicated 13.0 v while the trailer was plugged. Un plugged the panel showed 12.1v. I checked the little DC outlet inside the cabin and measured 16.3v.

I thought my VM might be in error, so I found another, measured again, and got the same readings.

So now the question: What do you others expect the inverter to charge the battery up to? Also, have you noticed a difference in the actual voltage delivered to the batteries and the voltage displayed on the power panel?

With this kind of reading, I will certainly try disconnect the batteries when I'm parked and plugged in to shore power to avoid over charging or over voltage. Comments?
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Old 08-05-2010, 06:05 PM   #2
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Hi Tank,

When a battery comes in the shop with a charge that high we can usually determine its sulfated and in need of replacement. The battery acts as a sponge and when its full will resist a charge. Not sure about yours but it would be easy to install new batteries and see how the inverter behaves?

Vin
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Old 08-05-2010, 07:05 PM   #3
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I have noticed a lot of small chargers will put out more than rating shows, but that high will cause sulfation if it hasn't already. They cut back after batteries charge, if the electronics is working. Did you smell hydrogen sulfide or rotten egg smell near battery charging area?
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Old 08-05-2010, 07:28 PM   #4
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Nope...no smell or anything unusual

I could not find anything unusual.

To be truthful...I know that I will have to buy new batteries sometime. Everybody does; don't they?

But, do I have to do it today? I think not. On any trip there is always a Walmart somewhere. Some I may be sleeping at. So it's not a lost opportunity if I defer buying new batteries.

I'm trying to decide what is normal, what will damage some part of the system. and what should I do now.

Today, it looks like my batteries will hold a good charge. The inverter does not get hot while trying to keep them charged. So, I'm comfortable with keeping them for the next month. What can go wrong?

The "overcharge" seems to tell me I will have to manually watch what is going on.

It does concern me that my VM will measure one voltage while the power panel indicates a different voltage, almost 20% less.
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Old 08-05-2010, 07:41 PM   #5
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[QUOTE=TankerIP;879939
The inverter
It does concern me that my VM will measure one voltage while the power panel indicates a different voltage, almost 20% less.[/QUOTE]

Don't you mean converter?

Such a difference between readings is of concern. Try your voltmeter in a house circuit and your car cigarette lighter.

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Old 08-05-2010, 08:15 PM   #6
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When i checked my batteries voltage at the terminals they read 12.1v. When i plugged into shore power they then read 13.8v. I think thats normal.
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Old 08-05-2010, 08:54 PM   #7
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I just replaced my Lifeline batteries because they measured 12.1 volts. They are about 50% charged. Last weekend we sed our trailer with hook ups and using a DVM I measured 13.6 volts at the converter, I should have checked the voltage at the batteries however, but didn't. Next time... oh and these measurements were with the new batteries.
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Old 08-05-2010, 09:21 PM   #8
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Most 12volt services like to operate within a certain range. I wonder about the fridge? Whatelse do you have that could be damaged by high voltage? When its plugged into the truck does it just hang about 14 volts? I would guess because your truck battery is ok that it will keep the alternator in check and not overcharge. Just get new batteries when you can. Vin
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Old 08-05-2010, 11:24 PM   #9
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Anything over 15 volts would indicate that the inverter is junk. Depending on the converter it may be designed to be junk or may be that it isn't working as designed. There are only two valid reasons to see 15 volts at the battery: 1) you have a temperature compensated converter and it's below zero in the middle of January, or 2) you pushed the "equalize" button on the converter and it's doing that or recently finished.
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Old 08-07-2010, 11:57 AM   #10
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Quote:
Originally Posted by r carl View Post
When i checked my batteries voltage at the terminals they read 12.1v. When i plugged into shore power they then read 13.8v. I think thats normal.
When plugged into shore power the batteries will read 13.8 v. regardless.

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Old 08-07-2010, 09:28 PM   #11
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Lightbulb Solved - Two Incorrect DVMs

Boy am I embarrassed. I had 2 DVMs with low batteries. The low batteries in the meters caused the readings of my trailer batteries to be high. I guess the volt meters make their readings based on differences from the installed battery. Sounds crazy but it's all that makes sense to me.

Both VMs had 9v batteries that were low and read 5v - - 4 v low. The meters measured my trailer batteries at 16+v, but the batteries were really correct at 12+ v (a 4v difference). What was my clue? I took the meters over to my truck and also read the same16v. that I had on the trailer.

Not sure what the moral of all this, but obviously you can't trust a digital meter to be absolutely accurate. I'll have to keep my eyes open for a good reliable replacement for the two that I have.

Thanks to all you for your advice.
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Old 08-07-2010, 09:34 PM   #12
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Did the meters get better with new batteries? Usually the calibration of a DMM is unaffected by battery voltage.

Meters do vary in quality. The one I have now I don't necessarily trust very much.
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Old 08-07-2010, 09:59 PM   #13
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Yep....I tested the trailer at the 12v inside outlet. Got 12.0v. The power panel indicated 11.8. Not sure what to think about the .2v difference but the reading is much closer than what I had before.
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Old 08-08-2010, 08:33 AM   #14
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Sounds like my HF 2.99 special meter.
I found a meter that plugs into the lighter socket, over the 10 years of using it, it's output changed, opened it up and found an adjustment on the circuit board. I wonder if the 2.99 has an adjustment rheostat.
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