One way to solve the TV to camper battery issue

tentcamper · 01-29-2015, 08:34 AM

One way to solve the TV to camper battery issue and add a MPPT solar controller. Mount it on the camper and charge up to 40 amps with voltage as low as 9.5 volts from the TV

Looks like a nice solution and charger. But ouch, the price.

Redarc BCDC1240

http://www.redarc.com.au/images/uplo...ger_130408.pdf

**ShrimpBurrito** · 01-29-2015, 09:25 AM

Yes, I installed a very similar model of theirs (no solar controller in it) awhile back. Very pricey indeed, but we exclusively boondock, so it works pretty well.

http://www.trailmanorowners.com/foru...ad.php?t=10587

Dave

tentcamper · 01-29-2015, 10:01 AM

bcdc1220 is not as bad. With currency conversion it's around $310 plus shipping.

Padgett · 01-29-2015, 11:28 AM

Lessee. $310 for yet another box vs move the TV next to the battery and use jumper cables ?

tentcamper · 01-29-2015, 12:31 PM

No, the idea is when traveling to fully re-charge the battery, or when you arrive at a CS to have it full charged battery, like it was when you started off. I agree jumper cable work better than the battery charge line if you are in your CS and need to re-charge and you don't have a generator or solar.

The issue is the voltage drop from battery to battery. There is not enough voltage difference at the camper battery, after the drop, to charge and run the fridge on a trip. You end up after a long trip with the camper battery having noticeably lower voltage then when you started your trip. In best case without running the fridge you may be able to re-charge the camper battery to 90% between CS's. The voltage drop on the battery charge line, just will not let you get it all the way.

But at the price for the solution, you have to do a lot of dry camping or be a near full timer. We mix up our camping between dry and sites with power. So it is not in my horizon.

**Bill** · 01-29-2015, 01:45 PM

Sadly, jumper cables from the tow vehicle are an extremely poor way to charge a battery. Been there, done that, got desperate enough to actually measure it, cursed and screamed, gave up. It will kinda trickle charge the TM battery, but not much more.

As near as I can tell, the problem is that when you hook up the cables, the voltage regulator in the tow vehicle is looking at two different batteries - the battery right there in the tow vehicle, and the TM battery out there at the end of the jumper cables. The regulator cannot sense two voltages at once, of course, so its reading will be pretty well dominated by the battery that is closest - the tow vehicle battery. But the tow vehicle battery is fully charged - or will be a minute or two after you start the engine - and so the regulator sets the alternator voltage to the maintenance level for that battery - about 13.5 volts. But 13.5 volts isn't enough to push much charge current down those cables and into the TM battery. In order to charge the TM battery, the alternator would have to be putting out 14.6 volts or so, which would badly overcharge the already-fully-charged tow vehicle battery. Result? The 13.6 volt maintenace voltage from the alternator produces exceedingly slow charge to the TM battery.

Note that this is not a voltage drop problem in the jumper cables (although that does contribute). It arises simply because the regulator can't see the TM battery clearly.

I believe that the jumper cable approach would work if you disconnected the tow vehicle battery. Now the regulator can see the undercharged TM battery clearly, and will raise enough voltage to charge it. But disconnecting and reconnecting a battery from a running engine is fraught with peril, as they say. I haven't tried it, and wouldn't do it.

Bill

scrubjaysnest · 01-30-2015, 06:55 AM

As Bill stated the problem is the alternator sensing the TM battery. The only solution has been discussed in other threads but to review. You must use a battery isolation system between the TV, TM, alternator and batteries. You must use large enough wire to over come the lose. Ford and Chevy generally have a relay isolation system as part of their tow package. Dodge and Jeep do not. Our 2008 Dodge charge line from the factory is 22 awg, way to small; the 2005 Grand Cherokee we have isn't much better. My parts cost to upgrade the Dodge and put in an isolation system was under $200 this included 40 feet of 8 awg added which parallels the 10 awg that came with the TM. This also parallels approx 9 awg I used to replace the Dodge original charge line.

In tow/haul with the Dodge at idle and the refrig on DC and once the isolator switches from the TV battery to the TM I have between 14.7 and 14.8 volts at the batteries in the TM.
For the two days at Kartchner SP we used the batteries without charging them. The trip from Kartchner to Rock Hound, 3 1/2 hours drive time, had the batteries at 13.05 volts after setting 6 hours with no load and no charging.

I don't know what if any isolation system other vehicle makers use.

A simple fix that will help if your TV has an isolation system is cut the ends off a 50 foot extension coord, 12 awg or better yet 10 awg, parallel the charge line all the way to the TM battery(s). Add a trolling motor plug/socket between the TM and TV and 30 amp breakers at the TV end and the TM battery end.

Padgett · 01-30-2015, 09:50 AM

Be carful when buying an isolation system as the less expensive ones are just a pair of big diodes and you have an instant .6v loss on both legs.

A good one like the Cole-Hersee 48530 200A unit will run about a benjamin. and be aware that "isolator" means just that. It allows a vehicle alternator to charge two different batteries while keeping them seperate at all times.

In an RV this means the starting battery is always available to start the engine while the coach batteries run the coach. (though most have a manual "boost" feature to put all in parallel.

It pulls about 5ma with everything off.

I learned more than I ever wanted to know about isolators & charger/inverters and dual output alternators (e.g. Lestek) while I had the RV.

tentcamper · 01-30-2015, 11:17 AM

scrubjaysnest, which isolation system did you get??

scrubjaysnest · 01-31-2015, 08:59 AM

Quote:

Originally Posted by tentcamper

scrubjaysnest, which isolation system did you get??

I don't remember the brand name but it is solid state, 120 amp model. As padgett said and Bill tell you the same there is about a half volt drop through the electronics. Except for interstate batteries this hasn't been a problem for us as I have always seen the alternator voltage rise to 15.5 volts on the input to the isolator. We got it at an RV dealer in MT after our 20 year old one failed. The first one was only 95 amp. The one we got in MT was on sale and with a GoodSam discount also it was about $100 bucks. They can probably be found in discount on line RV stores for about the same price. Bill prefers the relay isolation system because you don't have the volt drop. The business I was in we had to many relay failures so I don't care for mechanical systems subject to vibration.
Check out this link for additional solutions and pics

http://www.trailmanorowners.com/foru...ight=refrig+dc