Charging a house battery in a Van

socko12345

I have a 2010 Freightliner (Dodge/Merc-Benz) Sprinter with a house battery. The battery is connected to the Sprinter via an isolator, and I use the house battery to run accessories when the vehicle is off.

The charging voltage for the Sprinter is about 13.8 to 14.0VDC at the alternator, and I'm getting the same voltage at the house battery. I'm not sure, but I don't think I'm getting a good charge on the battery. I run the van for a minimum of 3hrs (at highway speed) about 5 days a week. My solar panels always charge at much higher voltages: 14.6 to over 16V (depending on the temperature).

Is 14V high enough to charge a 12V battery?

I need to replace the battery; is there a battery that would work in this application?

niel

Re: Charging a house battery in a Van

14v is probably not enough and most lead acid batteries will need about 14.3v or higher to get a full charge. the problem is most likely the isolator is using 2 power diodes to keep the batteries separated, but this will introduce a voltage drop of between 1/2v and 1v. vrla type batteries are able to charge with lower end volts around 14.3v or so, but only the agm can take the high charge/discharge rates. in any case the isolator isn't bringing the voltage up high enough to properly charge the batteries all of the way. maybe try switching between the batteries with a heavy switch like this one and get rid of the isolator. btw, don't put both batteries on at the same time and you could optionally get a small pv and use it to make up for the final charge to the batteries through a controller.

http://www.solar-electric.com/basw1300amp.html

socko12345

Re: Charging a house battery in a Van

Niel, thanks for the speedy response!

I'm measuring 13.8 to 14 at the stock battery, AND at the house battery---no measurable voltage drop. The stock (engine) battery is the original, and has lasted for 3 years now, while I can only get a house battery to last 6 months. If the stock battery can get a good enough charge to last 3--7years, what am I missing? Why do my house batteries keep tanking? FYI, I've been pretty careful not to let the voltage drop below 12.0V on the house battery.

inetdog

Re: Charging a house battery in a Van

socko12345 wrote: »

Niel, thanks for the speedy response!

I'm measuring 13.8 to 14 at the stock battery, AND at the house battery---no measurable voltage drop.

But what are you measuring on the alternator side of the double-diode battery isolator? That should drop and equal amount of voltage between the alternator and each of the two batteries, leaving the battery voltages equal but low.

One difference is that the stock battery is never called upon to deliver a large part of its capacity; so as long as it can supply the cranking current for the engine it does not matter if it is fully charged. The house battery, on the other hand, will be called upon to deliver a much larger portion of its stored energy and will not be immediately recharged by the running engine the way the cranking battery is. The cranking battery may also be of different physical and chemical construction, allowing it to operate better with the reduced charging voltage.

Some recommend tweaking the alternator voltage regulator to increase its regulating voltage by the amount of the diode drop. But that can lead to other problems. Some manufacturers produce a system that does the isolation using relays controlled by an intelligent module instead of just diodes.

There is an extensive discussion of dual battery strategies (biased toward their solution, of course) at http://www.smartgauge.co.uk/technical1.html . (Over 100 pages of really good stuff, including the authoritative reference on wiring batteries in parallel to make up a battery bank.)

BB.

Re: Charging a house battery in a Van

You need a "battery charger"... There are DC to DC battery chargers:

http://www.powerstream.com/DC-input-chargers.htm
Auxiliary Battery Charger (I think this will work--However, it is written for house battery charging starting battery--you would "wire it backwards")

And, you could use an AC inverter (on the engine side, inverter only runs when engine is running) and an AC battery charger (to charge the house side).

It sounds like your house battery is never getting up to "full charge".

Another option, plug the house battery into a good quality AC battery charger at night... That should help a lot. By the way, do not use a "locking plug". Use the normal straight bladed plug (more than a few people have backed away and yanked an outlet out of the wall when they forgot to disconnect).

-Bill

Shadowcatcher

Re: Charging a house battery in a Van

Unless I have missed it, part of the equation not addressed is the type, capacity and depth of discharge of the House battery. If the house battery is not a true deep cycle battery, or if you are consistently taking it below 50% state of charge it will lead to a short life.
A VOM is your friend, check the voltage delivered at the house battery, what is it really.

niel

Re: Charging a house battery in a Van

socko,
it isn't a voltage difference between the batteries, but rather a difference from the alternator output to the isolator output. it may be just as easy to measure the input voltage of the isolator to either of the isolator outputs to the batteries. i'd be willing to bet the alternator is at a higher voltage than your isolator output. if by chance it isn't at least 14.3v at the alternator then you may need to talk to somebody about that regulator so that it will be adjusted upward for proper charging volts. the specific battery you use you will need to check with the manufacturer on its proper charging volts too. with different batteries you could run into a problem here too as each may have different requirements.

vcallaway

Re: Charging a house battery in a Van

I realize this is a bit old now, but I will chime in on what I did.

First off, not a fan of diode based isolators. Instead I prefer to use a constant duty power solenoid. This 100A one from Grainger is one I've had good luck with. In my Suburban I run dual batteries. The solenoid has two wires connected to the on post. Both have diodes inline. One is connected to power that comes on with the key in the on position. The other to a push button that gets its power from the primary battery. The reason for the push button is so if I run the aux battery too low to trip the relay I can do a jump start. Works GREAT.

Second option for a few dollars more is this voltage sensitive relay. It connects the two batteries when the voltage reaches 13.7v, meaning the engine is running. It is designed for exactly what you are asking for.

inetdog

Re: Charging a house battery in a Van

vcallaway wrote: »

I realize this is a bit old now, but I will chime in on what I did.

I just remembered that we send people off to smartguage.co.uk for battery wiring information, but the true purpose of that site is to discuss battery isolation schemes and to demonstrate the advantages of their solution. :-)