Community Forums

Rebthom · 03-15-2015, 07:59 AM

Hi, just wondering how long it takes to fully charge an RV battery when travelling (via the truck). Say 2-3 hours?

J Birder · 03-15-2015, 08:49 AM

That pretty much depends on the size of the batter(ies), on how discharged they are, and on how much current you can transfer. In any case, 2-3 hours will not be enough time.

The wire gauge between the truck and the battery will generally limit the charge current to no more than about 10 amps. So, if you have drawn 100 amp-hours from the battery, it will take about 10 hours of driving to replace it.

Joel

gebills · 03-15-2015, 10:17 AM

Quote:

Originally Posted by Rebthom

Hi, just wondering how long it takes to fully charge an RV battery when travelling (via the truck). Say 2-3 hours?

Good Morning Rebthom: J Birder has pretty well answered your question. From the way you are asking your question, sounds like you may only have a partial discharge. If that were the case, you TV will likely top your RV batteries off if they suffered from only a light parasitic discharge in storage. If your discharge is more significant, then as J Birder has suggested, it will depend on the level of discharge as to how long it will take to recharge totally.

If you have a significant discharge and are going to park and camp where you have no 110V power available, simply plan ahead and do the maintenance on your battery(s) by checking the battery liquid level (add only distilled water) and charging the battery(s) by pulling to the closest 110V outlet or pulling your battery(s) out and taking them to the nearest outlet/battery charger location. Bare in mind that if you were going to tow and camp where there is no 110V to plug in your RV, then your options become more limited as to how you would handle a dead battery during a planned camp departure while your landing gear is extended. Many options exist, and most involve a cost of time, fuel or parts/materials, i.e. pulling batteries from the RV and taking it (them) to a location with 110V/battery charger to recharge, buying and inverter (converting 12VDC to 110VAC) to run a very small battery charger off of your TV, yada, yada, yada; the options go on, and of course get more spendy. I've probably added enough information to confuse you, so...... nuf said......

wa8yxm · 03-15-2015, 12:14 PM

2-3 hours is a "Top off" (Starting at 90% or more full)

IF your truck can pump major amprage6-8 hours from 50%..VERY VERY VERY few tow vehicles can charge that fast

How to calculate

you need a clamp on ammeter,, and you need to know both SOC and Size of Batteries (C/20 rate).

State of discharge = 100-state of charge percent.

Multiply capacity by state of discharge to get Amount of Recharge

With bateries at 50% SOC (Deep cycle) Or 75% (Marine/Deep cycle) hook up to truck, Clamp on the proper wire (JUST the one wire) sart truck and rev up to around 2500RPM

Measure current

Divide Amount of recharge by current.. Multiply that by 1.15

You will be close.

Rebthom · 03-16-2015, 04:24 AM

Thanks for the answers, some a little complex for me, but I get the idea.

nothermark · 03-16-2015, 04:57 AM

FWIW some clamp in meters will measure DC and some will not. If you are buying one check that before purchasing. ;-)

caissiel · 03-16-2015, 08:03 PM

For years I travelled south every fall and we took our time while stopping at WM and FJ and after 4 days the batteries would no longer operate the inverter and they would just die needing the truck to Idle to boost them some.
Batteries needed change at only 2 years old.
Found out the hard way, with larger wires to the trailer plug direct from the truck batteries, and dead batteries the max amperage was 23 amps.. The same when using my power plant feeding the converter charging my batteries.
Finely I installed 200 watt Solar panels with MPPT controler and the 3 batteries are 100% charged by noon.
The truck could only charge the batteries to 12.4 volts due to line lost, and I was leaving the CG with 59% charged batteries. So when leaving I was 40% down already on the batteries and the truck barely improved the situation.
This is my observation. And solar has served my old batteries well including the truck batteries on the road. When we travel the solar charge while on the road and parked and the batteries never drop below 12.0 volts at night with living power on. Next day the batteries are back to 14.8v charge in no time. To me the truck charging RV batteries is a lost cause unless on is prepared to travel all day like 12 hrs. Just in battery replacement cost in 2 years the cost of my Solar is paid for. And Its no fancy system that works well for us.

franknj · 03-18-2015, 05:07 AM

Last year I was asking the same questions you are now and always looking for ways to charge the batteries. I would leave the truck idling to get a little extra juice or fire up the Honda 2000 generator and let that charge. This winter, like others have done I broke down and installed solar and the batteries have been topped off constantly. I have a similar setup on my boat that has been charging for several years without fail. I know solar wasn't part of your question but since it has been so effective I wanted to point it out as an option. We used two Kyocera 135 panels and an MPPT controller. For reference: http://www.irv2.com/forums/showthread.php?t=236077

ramblinboy · 03-18-2015, 11:09 PM

My house batts are under my second step in the entrance to my MH. So how do I charge the batts from my solar panel with a step missing?
Thanks, Rb

franknj · 03-19-2015, 04:55 AM

I'm not sure I understand your question @ramblinboy. Not sure if you are referring to a physical step (a stair) or a step in a solar diagram. Wherever your batteries are located there has to be wires running to\from them. The solar wiring would be run from the roof to wherever you end up putting your solar controller. The controller takes the output from the solar panels and acts as a battery charger using output from the solar panels (commonly called a charge controller or controller for short). Then wire goes from controller to your batteries. The route of the wiring and location of the controller are specific to your model MH. There is a cutoff switch and breaker in the circuit but it's that simple. That's really all you need to charge batteries with solar. Once it's done just forget about it.

I strayed from the original question a bit but as someone mentioned above the time it takes to recharge depends on many things including depth of dischsrge, type of batteries and capacity etc. As gebill mentioned check the water level in the batteries if you have wet cells. I found dead batteries this year and realized they went dry. My fault for forgetting. I have AGM cells this summer I plan on installing after the snow melts. One less thing to worry about.

ramblinboy · 03-19-2015, 09:18 AM

Thanks Frank. My controller will be as close as possible to my batteries to avoid line loss. The solar kit comes with a charging cable with ends like a booster cable. To get at my batteries and hook up to them Id have to remove one top of the steps to enter the motorhome. They are in a battery box inside one of the steps. Is there a way to make pig tails for one negative connection and one positive connection and keep the step covered?

franknj · 03-19-2015, 12:38 PM

You can buy pig tails and crimp the battery ends you need or have them custom made. I bought all my equipment from Northern Arizona Wind and Sun at www.solar.electric.com. they have really helpful solar engineers to help with questons. There are a lot of places to buy parts but not everyone will help design your system and answer questons. Give them a call and see what cable options you have. There are places that make just cables as well. Let us know how you make out. Solar is one of those things that is simple and very effective.

ramblinboy · 03-19-2015, 02:09 PM

thanks again Frank. What I can do is drill 2 holes through the step riser and insert 2 bolts with the heads protruding slightly. I can connect my solar panel control box to those points to charge the batts.
The heads should be able to be plastic capped to avoid any chance of a short circuit.
Inside the battery box the bolts can be connected by short lengths of #2 wire on copper ring ends.
Ill still have wires from the solar panels on the ground going through the door and up the step during charging but at least the top of the step will be in place.
I could connect my inverter to those points as well when using it to drive AC appliances.
Does sound kinda jury rigged though. it may be better to find a way to run those charge points and put the inverter into my first storage bay and be done with it.

franknj · 03-19-2015, 04:41 PM

Start a new thread on solar wiring ideas needed for MH to solicit ideas from the forum. I can't visualize your setup but there's a lot of juice running through the batteries. I'd be very causious about jury rigging when lots of amperage is in play. Just my two cents is do it right the first time and you won't regret. You won't remember the extra expense after a short while but a half baked job is in your face and head everyone you see it.