Saturday, December 10, 2022


Ask Dave: Can I add a portable battery charger to improve slow slide function?


Dear Dave,
While plugged into shore power, I would like to use a portable battery charger for my two deep cycle batteries. Any problems with this scenario? After two or three days the sliders are very slow to come in when packing up. —Mitchell, 2003 Thor Southwind

Dear Mitchell,
You can use a portable battery charger; however, there should be enough power from the converter when plugged into shoreline power. Let’s take a look at your battery bank and charging system.

Southwind is a Fleetwood product and Thor is a different company. Fleetwood typically installed four 6-volt batteries connected in series, which is one battery connected to a second, positive to negative, which provides a 12-volt “bank.” The second two batteries are also connected in series, then the two banks are connected parallel, which is positive to positive, negative to negative. This provides two 12-volt banks and doubles the amp hours.

Thor typically used two 12-volt deep cycle batteries connected parallel so it would also have double the amp hours. This is a setup with two deep cycle batteries and the engine start battery in the same compartment.

In both setups, there is 12-volt deep cycle power available to run the house lights, vents, water pump and other items such as the slide mechanism. And in both cases, I would bet these are not the original batteries as the typical converter/charger that is in either the Fleetwood or the Thor does not condition the batteries and they sulfate after just a few years.

Lead-acid batteries

Lead-acid batteries simply store energy. As that energy is drained, sulfation collects on the plates and requires a high-voltage charge known as the bulk stage to break it up. This can be 14-16 volts, then goes into an equalizing and float charge. Your rig has either an all-in-one distribution center with a converter attached that provides a charge to the batteries. Or it has the circuit breakers in their own enclosure and a stand-alone converter such as this WFCO model that is hidden under kitchen cabinets or under the bed pedestal, as it runs a little loud and noisy.

Both versions start with a 13.6-volt charge when the battery needs a charge, which is at about 50% drain of the battery. When the battery reaches 12.6 volts, which is fully charged, the converter drops to a 13.2-volt charge rate, which is a maintenance charge. This 13.2-volt charge should be available all the time the unit is plugged in and sufficient enough to run the slide mechanism without a drop in voltage.

Technically, the converter is a battery charger, so adding a portable charger would be like hooking up two battery chargers to a battery. Once the battery hits 12.6 volts they would both go to 13.2-volts maintenance. So, even though it won’t hurt, it won’t help either.

Things to consider

I think it’s more important to figure out what is happening during the charge, what condition your batteries are in, and why you have a voltage drop after 2-3 days. A few questions:

Are you plugged in all the time and notice a voltage drop? If so, you need to get a multimeter and periodically check the voltage available at the battery from the converter. If you are not getting 13.2 volts consistently, then your converter is not working as designed, or you are getting a voltage drop from the 120-volt source.

Back in the late 1980s, I was at Winnebago and we had a large unit called the Elante, which had a 30-amp distribution center. If you were using several 120-volt appliances such as the roof air conditioner and other items, the converter was not getting enough power and the batteries would actually drain when plugged in! Didn’t seem possible, but we had several issues. Using a multimeter will help identify if your converter is working correctly.

If you are plugged in and having this issue, I would suggest using a multimeter on the batteries as you retract the slides and see what is happening there. I would also suggest checking the 120-volt system, as well. You can get a voltage tester from Klein on Amazon.

Keep this plugged into an interior outlet and verify you have close to 120 volts at all times. If you see a significant drop when retracting the slide, then you have a power issue from the pedestal or distribution center.

 You might also enjoy this from Dave 

When RV is plugged in to shore power, why isn’t house battery charging?

Dear Dave,
When my RV is plugged in to shore power it doesn’t charge the battery. Is there a fuse inside the charger? When I turn on power I hear the cooling fan turn on briefly. There’s power going in but nothing out. —Claire, 2017 Winnebago Minnie Winnie 25B

Read Dave’s answer

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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