Checking voltage on connected 6 volt batteries

opnspaces wrote:
Yes as MFL posted. The batteries will have an abnormally high voltage right after you take them off the charger. But that is what is called a surface charge.

Good information. Thank you.

Yes as MFL posted. The batteries will have an abnormally high voltage right after you take them off the charger. But that is what is called a surface charge. It has no real substance and will deplete quickly. So you either have to let them sit with no load or charge for a few hours to dissipate the charge before taking a reading. Or apply a decent load to pull the surface charge off.

With a car the recommendation is to turn on the headlights with the engine off for one to two minutes to dissipate the surface charge. Then turn off the lights and you can take your voltage readings. Since the trailer doesn't have headlights and most interior lights are LED's the furnace is the easiest way to put a decent load on the batteries.

Another way to look at this is picture your battery as a tank of water with the water level indicating the state of charge. Now blow a big soap bubble on top of the water (this is your surface charge). It will suddenly look like there is a lot more charge in the tank. But of course the bubble has no substance so if you touch that bubble it will pop and leave you with the true level in the tank.

LeBout wrote:
Question: when on shore power, do the batteries need to be disconnected from the trailer before putting a voltage tester on them?

I'm gonna say yes. I can think you'd be getting an accurate reading if you show charge voltage from the converter.

To answer your question...check after it shut off. When a battery has been charging, then just disconnected, it will show a higher state of charge. If you have time to wait, battery at rest, no draw/no charge, for several hours, that is a good time to test. As mentioned, a short load will remove the recent high charge reading, so you don't have to wait to test.

Jerry

opnspaces wrote:
Yes, depending on what you're testing for. If you want the batteries state of charge you need to disconnect the shore power cord. But then you should turn on a load like the furnace and let it run for about 2 minutes first to remove the surface charge from the shore power.

Should the reading be taken with the furnace still running or after it has run and is now off?

Yes, depending on what you're testing for. If you want the batteries state of charge you need to disconnect the shore power cord. But then you should turn on a load like the furnace and let it run for about 2 minutes first to remove the surface charge from the shore power.

However, if you want to check if your charger is working, take a battery reading with the shore power disconnected. Then plug in shore power and take another reading. If the charger is working you should see the voltage jump up to at least 13.5v.

I would say yes(just unhook from shore power) or flip the breaker for the converter to make sure it is not charging batteries as you take your reading.

Question: when on shore power, do the batteries need to be disconnected from the trailer before putting a voltage tester on them?

Here is a simplified pictorial on how to connect two 6V Batteries in series to get 12VDC... after connected in this manner then just conside these two 6VDC batteries connected in serial as a 12VDC battery...


Google Image...

When connected in series note that your DC VOLTAGE will double but your AH rating will stay the same as one 6V battery rating...

If you want to increase your AH rating install a second series connected group of 6V batteries in parallel to the first group. Using the pictorial above of 220AH batteries you can get 12VDC at 440AH capacity by doing this...

Here is a schematic of how this can be accomplished...


Roy's image

Roy Ken

A battery is defined as two or more cells connected pos to neg . Two six volts equal one battery of six cells or 12 volts just like cannons !