Battery Charging via TV

Monterra · 10-11-2013, 06:22 AM

I've got 2 new group 24 Interstate RV/Marine batteries in parallel and will be boondocking for up to 3 nights back-to-back on our way south next week (plus the return trip). I expect we will be using the furnace a fair amount, at least for the first 2 nights.

Can anyone give me a sense of how effective the TV will be to charge the batteries when travelling? I expect to be on the road 6 hrs per day.

Thx for you thoughts

raspivey · 10-11-2013, 06:28 AM

You'll be fine as long as you are conservative with the lights. I do 2 - 3 nights on two group 24's without charging and don't have any problems. 6 hrs. probably won't put it all back, but should give you plenty for three days.

Since those are new....make sure you get a good charge on them before you leave, they often aren't off the shelf (FULLY charged, that is).

Monterra · 10-11-2013, 07:14 AM

We did 3 nites the other weekend without a problem but we did not use the furnace. I don't know how big of a hit that will be. Of course, that will depend on the temps.

**KyDan** · 10-11-2013, 07:22 AM

Two thoughts--
A furnace is a battery hog. I can get about 1 night per battery if I set
the T-stat on 55 and the outside temp is near freezing.
55 deg inside a trailer is pretty cold. You want to have flannel sheets and
a down comforter or a down sleeping bag opened up as a comforter.

Many folks have found they get little charge from the TV. The reason is
the engine alternator voltage regulator sees the engine battery as being
charged and cuts back the voltage so as not to fry the engine battery.
The trailer batteries are much farther down stream and don't see enough
voltage to get much of a charge.

3 days is not much of a problem for us if we don't use the furnace more
than just once or twice in the morning to take the chill off.
Baking a batch of (canned) biscuits will greatly help to warm a chilly trailer in the morning!

Good luck!

**Herk7769** · 10-11-2013, 07:42 AM

The alternator of your truck is a very ineffective battery charger. (See attached PDF for why that is so.) Basically, the alternator is a single stage charger designed to replace the tiny amount of charge used to start your truck and supply the DC current required to power the truck's normal demand. (Voltage recovers almost immediately, but capacity takes HOURS at the reduced charge rate as the battery voltage increases. (see graphs)

Anyone who goes to work and then comes home in the dark while commuting a short distance (less than 30 minutes) will tell you that the alternator does not replace what was used to start the car and run the headlights/heater in that 30 minutes resulting in a net loss of charge. That battery will not have enough capacity to start the car by the end of winter without putting it on a dedicated charger.

I would rent (or buy) a small 1000 watt generator from Harbor Freight and a dedicated stand alone battery charger to top off your battery stack instead of the sorry job your TV is going to do.

Running the truck all day to (maybe not) get the batteries through the night on day 2 could suck big time.

Obviously this will depend on how little you use the batteries for other high draw items (lights and water pump) and you do not use an inverter at all.

KMP44 · 10-11-2013, 07:52 AM

And if you haven't already - make sure your tv has all the required fuses and relays installed to power the prong that supplies the current to charge the battery.

Learned the hard way that mine didn't when the 12v frdige in the popup completely drained the battery on the way to a 5 day dry camp...

Charging with the tow vehicle may not be the best option, but for sure you don't want your batteries being drained while you go down the road. If nothing else, the power from the tv will maintain your charge.

**Herk7769** · 10-11-2013, 08:03 AM

Quote:

Originally Posted by KMP44

Charging with the tow vehicle may not be the best option, but for sure you don't want your batteries being drained while you go down the road. If nothing else, the power from the tv will maintain your charge.

This is exactly right and what the charge line from the TV is supposed to do. It will not replace lost house battery capacity in any reasonable amount of time.

**bikendan** · 10-11-2013, 11:18 AM

as Herk said, your TV will only provide a trickle charge. probably the worst way to recharge your battery except while driving.
and as others said, the furnace is the big battery hog on your trailer. the less you depend on it, the longer your batteries will last.
but we can go 3-4 days on our two 12v batteries but we rarely need the furnace. and we have a Honda 2000w just in case we don't.

Monterra · 10-11-2013, 02:17 PM

Thx all for you comments. I used to live in northern Canada and that is where I learned about 'square' tires and battery blankets. Certainly, if your battery is cold, it takes MUCH longer for it to accept a charge. Hence, the need for an electric blanket for the battery.

**Herk7769** · 10-11-2013, 03:36 PM

Quote:

Originally Posted by Monterra

Thx all for you comments. I used to live in northern Canada and that is where I learned about 'square' tires and battery blankets. Certainly, if your battery is cold, it takes MUCH longer for it to accept a charge. Hence, the need for an electric blanket for the battery.

This is exactly right.

Cold reduces the batteries ability to deliver or accept electrons due to the slowing of the chemical reaction in the electrolyte. Maximum available capacity is reduced when the temperature decreases.

rotorhead1250 · 10-11-2013, 04:23 PM

If ya use an automotive charger, can ya leave the batteries connected to the camper while powering the camper and charging the batteries?

**Herk7769** · 10-11-2013, 05:15 PM

Quote:

Originally Posted by rotorhead1250

If ya use an automotive charger, can ya leave the batteries connected to the camper while powering the camper and charging the batteries?

I use my disconnect switch when using a dedicated 3 stage charger (like Ship-n-Shore). If you do not have a disconnect, I would remove the ground wire from the battery.

**KyDan** · 10-12-2013, 07:37 AM

Quote:

Originally Posted by rotorhead1250

If ya use an automotive charger, can ya leave the batteries connected to the camper while powering the camper and charging the batteries?

I never disconnect batteries to charge.
In fact I've "dual charged" by having my trailer plugged into a generator
and used a stand alone 25 amp automatic charger at the same time.
The onboard charger and the standalone both put out less charge
when doing this but the total is more than either one by its self.

This is just me- how I do it.
YMMV.

RvBill3 · 10-17-2013, 05:39 AM

Check the owners manual for your TV. My Chevy Avalanche has a "charge" line on the 7 pin connector like most or all do. But the owners manual says you have to connect the wire under the hood. It also has a fuse that I had to replace once. It further says that if you use the tow-haul mode it runs the alternator at a slightly higher RPM (in other words the engine idle speed is kept higher) to provide a higher charge current on the charge line. When we had a TT it did provide enough to charge the battery to about 90% in a 5-6 hour drive.

Monterra · 10-17-2013, 07:40 AM

The TV manual does not mention the power circuit on the 7 pin connector. However, I did locate the fuse for this circuit and it indeed needed to be replaced. Well, I'll know within a week how well the TV tops up the batteries.

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