Battery Charging while towing

[Tomahawk]

Originally Posted by Bobertgoes

So, since you were plugged in for many days and I assume your plugged in charger is good and left the battery/batteries top..... not a scientific one bear in mind.

After reviewing all the responses and the data from the trip, I think my truck is providing little to no charging. Could be resistance in the 7-pin plug. The converter and Solar Charger are performing correctly. Based on the data, I think the batteries are performing well.

Here is a summary:
1. Batteries on converter for 5 days
2. Unplug and leave about 7PM stop over night, forget to turn off rearview camera.
3. Wake up and leave for SEKI at 10
4. Arrive SEKI and setup by 3, Batteries at 12.5V (90% based on trojan batteries chart, 70F). Dry camping from here out.
5. A little sun, batteries maintain 12.5, last check at 8:30
6. Batteries at 12.4 (90% at 60F) at 7:30 AM after lights plus heater on at 5AM. Over night temp was mid 40s
7. At 7 PM after sun for 5 hours, batteries at 12.7V (100%+)
8. At 7 AM, after lights and heater at 5 AM, 12.5V (close 100% at 60F)
Repeat 7 and 8 for next 3 days.
9. Wake up in morning and put up solar prior to sun getting on it. Run in slide. Drive home 6 hours with backup camera on.
10. Run out slide. Plug in converter at home. Converter working hard to charge battery.

Solar is keeping the batteries charged when deployed. The batteries seem to hold charge well over 12 hours with our usage.
I am still going to test the truck with the battery connected to see the voltage at the battery from the truck. I will clean the 7 pin really well and repeat the test.

[Bobertgoes]

1-10 all looks normal... What's the question again?

Are you sure your battery charger at home is good? Is your assumption based on "battery charger working hard"?

Is your truck battery good? The truck battery somehow draining the RV battery is unlikely though.

I originally had 200 watts of solar only and originally had two GC batts. I had a switch to disconnect the truck from the trailer so even while driving I did not charge from the alternator, the solar did everything ever needed.
When your battery is low I would check the amperage coming from the solar charge controller to the batteries. You will need to buy the tool. When you have dead or low batteries is when the solar will be putting out its highest amperage (voltage will remain constant). Is the solar charge controller putting out high amps for low batteries? If not then look there for issues. ...bad controller, wire size, connection terminals, loose wires, corrosion???

If you truly want to do serious charging from the alternator then you can completely skip around the vehicle's charging circuit and thin wiring. Use 6g wire and run from the alternator to an Anderson plug to another Anderson plug on the trailer to more 6g wire to the battery (or DC-DC controller for you lithium guys). On the truck near the DC source I would put a solenoid switch so you can turn it off so the big wire is not electrified all the time (when not towing or when u do not need alternator power).

Hint: start the 6g wire at the starter motor as there is already heavy wire run from the battery to the starter motor that is available and unused while driving.

But again, your solar should provide all the charging needs if you have sun. If not, then add more panels, which would be the easiest fix IMO.

You mentioned "heater". Is this a propane furnace? those do eat up a lot of power also.

[Tomahawk]

Originally Posted by Bobertgoes

1-10 all looks normal... What's the question again?

Really I am just surprised that on the way there that the after no use and four hours on the truck, the batteries weren't 100% when we arrived. Then after a night of use, I was surprised 6 hours of driving wasn't enough to replenish the batteries.

Some responders have said 3 amps is typical so that would 18 AH sent to the batteries on the way home. That would be a little less than 10% of the battery capacity. I suppose I could have used closer to 20% overnight since I let my wife run the heater even more and ran the slide out a twice on the trip home.

Thanks for the input.

[theoldwizard]

Originally Posted by CamperLifer

Some TV are different than others. Mine charges the TT batteries while towing.

Originally Posted by kmrofrano

For a while GM had ECU controlled alternators, I "retired" from the auto mechanic world in 2011 ...

Retired auto engineer. Starting in about 2000, ALL manufacturers of light duty vehicle (cars and pickups up to 1 ton) went to "smart charging" system. They all work similarly but not exactly the same.

Once the vehicle has been started and running for a sort time (typically less than 15 minutes) the ECU will tell the alternator/regulator to cut back the voltage, typically to about 13.2 voltages. Probably a bit less at the trailer connector. Adding a large conductor cable directly from the battery will not change the voltage !

13.2V will "maintain" a battery, but it will not recharge a partial drained one.

[theoldwizard]

Originally Posted by Bobertgoes

Hint: start the 6g wire at the starter motor as there is already heavy wire run from the battery to the starter motor that is available and unused while driving.

Waste of time and money ! See my previous post !

[Bsipe01]

with the alternator being controlled by the ECU, getting the alternator output voltage high enough (around 14.X volts) would require re-programming the ECU. Not likely to be an option. Unless the tow vehicle has provisions for such application, it would be a complex undertaking to make it work reliably. Victron and others make a DC-DC charger that can boost the voltage and take care of the charging. You'd still need to insure that the wire is sized adequately to avoid voltage drop.



One aspect of this discussion that seems to have been overlooked is fusing. Any connection to the battery, starter, or other high amperage potential must be fused at the source to prevent a fire in the event of a short. (Think: pinched wire) The function of the fuse is to protect the wire.

[Dave Pelletier]

Common issue on the Super Duty forums; trailer has to be detected, brake engaged, voltage varies depending on the ECM, etc.

I think what the OP ie experiencing is completely normal and I simply don't expect my trailer batteries to get much (if any) charge while being towed. My 340watts of solar does a fine job though.

If my usage was such that it was important to properly charge the batteries while towing, I'd run an new wire and a DC to DC charger.

Dave

[garywilson]

A few weeks ago I spent a couple of weeks at GSMNP, no elec or water at sites, so the generator ran for a couple of hours every day to get batteries up to 85-90%.

When I left GSMNP in the morning my batteries (2-6V golf cart 230A from Sams) were at about 80%. When I stopped 180 miles and 3 1/2 hours later they were up to 95%.

I was surprised at the amount of increase, much more than I expected. I didn't put a meter on the rate, but seems like that would be around 9A hour. TV is a 2016 Silverado 2500 with heavy duty alternator and two batteries (spare battery is for ie snow plow).

Running in the trailer was propane ref, radio, propane detector.

Seems pretty good to me....

[Marine359]

Originally Posted by garywilson

A few weeks ago I spent a couple of weeks at GSMNP, no elec or water at sites, so the generator ran for a couple of hours every day to get batteries up to 85-90%.

When I left GSMNP in the morning my batteries (2-6V golf cart 230A from Sams) were at about 80%. When I stopped 180 miles and 3 1/2 hours later they were up to 95%.

I was surprised at the amount of increase, much more than I expected. I didn't put a meter on the rate, but seems like that would be around 9A hour. TV is a 2016 Silverado 2500 with heavy duty alternator and two batteries (spare battery is for ie snow plow).

Running in the trailer was propane ref, radio, propane detector.

Seems pretty good to me....

95%? As measured by what? I don’t think a battery can gain voltage thru a 7-pin without the aid of a dc/dc controller.

Keep in mind, when you looked at voltage after your drive, you’re taking a snapshot of battery voltage after being subjected to a charge amperage. It will always be higher than resting voltage. Lead Acid batteries don’t hold the higher charge voltage for long. If you looked at the battery voltage a couple of hours later, you would see a lower voltage.

[garywilson]

Originally Posted by Marine359

95%? As measured by what? I don’t think a battery can gain voltage thru a 7-pin without the aid of a dc/dc controller.

Keep in mind, when you looked at voltage after your drive, you’re taking a snapshot of battery voltage after being subjected to a charge amperage. It will always be higher than resting voltage. Lead Acid batteries don’t hold the higher charge voltage for long. If you looked at the battery voltage a couple of hours later, you would see a lower voltage.

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Sure it will gain some... Maybe my memory from last week faded or I read the number wrong?

As measured by a fancy little meter I put in a few months ago. Depending which button you push, it shows present amp gain or loss, voltage, amps, or battery percentage remaining. It is a nice improvement over just using a volt meter. I can easily determine amp usage change turning on a light, peripheral loss, furnace fan, running generator, etc. If everything is off (except for peripheral radio, propane detector, and whatever) I lose about 1 AH with my 3 year old batteries.

In this particular case, reading was taken before I hooked up to leave and about 40 minutes after I arrived at destination and had unhooked. I'm estimating the time after arrival that it takes to park and get completely set up. I expected a gain of a few amps but got more than I expected.

Back in the 'old days' around 1970 when pop-ups didn't have an on-board charger and the only way to charge was through the TV, weeks would go by without a charge other than from the TV. Used only for a water pump and lights batteries lasted a long time. We just ran a hot wire from the TV battery to the single 12V on the trailer to keep it charged. Ignorance is bliss.

I'll drag it around again next week for an hour drive after using it for a couple of days and see what it says. This time I'll write it down.

[Bobertgoes]

Called "surface charge". You see a higher voltage right after a charge than the batteries actually will have. Once a little power is consumed off the bat then that voltage will drop fast.

I bought a DC-DC charger to protect my alternator from the lithium battery (which wants to pull as much amperage as the alternator is able), but
the real benefit of dc-dc charging is that it can take weak low voltage and ramp it up, though in intervals, to the needed charging voltage. For FLA consider dc-dc too. It solves so many problems.

[garywilson]

Originally Posted by Bobertgoes

Called "surface charge". You see a higher voltage right after a charge than the batteries actually will have. Once a little power is consumed off the bat then that voltage will drop fast.

I bought a DC-DC charger to protect my alternator from the lithium battery (which wants to pull as much amperage as the alternator is able), but
the real benefit of dc-dc charging is that it can take weak low voltage and ramp it up, though in intervals, to the needed charging voltage. For FLA consider dc-dc too. It solves so many problems.

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Ok...I'll check on a rapid drop after usage too.
I guess read battery before & after tow, check every hour for a few hours, then put a known load on it. Won't be a very good test this time as I'll only be driving a little over an hour.
Unless I use the furnace and draw it down quite a bit I seldom have to charge it when I just do one night at a place and then move on.