Battery not charging during tow

[rcorkum4]

Recently I've noticed that the coach batteries on our Sprinter 250RBS trailer are not charging when being towed. I left Portland, OR with batteries (2 x 6v golf cart batteries in series) at 1/2 charge and drove about 3 hours. Checked the batteries on arrival and found them still at 1/2 charge. I disconnected the + battery cable at the coach battery and measured about 13.6 volts across the battery cable and the chassis ground on the trailer with the TV running. I don't have an ammeter so am not able to see how much juice is flowing.

Any suggestions for trouble shooting further?

They charge just fine when connected to shore power.

Ron

[Rkymtnman]

Do you know if your coach batteries ever charged off your tow vehicle?

I ask because on mine (2005 GMC Sierra), you have to place a fuse in the "Stud #1" position in the under hood fuse box to "energize" the power circuit back to the 8 pin round connector on the trailer. From the factory, GM placed a shunt in this position and it needs to be replaced with a fuse. I believe I used a 30A fuse on mine.

The "Stud #1" position is in the upper left hand corner and is indicated on the "map" under the panel cover.

[Festus2]

Not sure about your unit but on ours, if connected to shore power, the RV interior battery indicator always shows full charge - regardless of their actual charge state. If your batteries are in poor condition or aging, they might not be able to maintain a charge while under load or capable of being fully charged.
I would check their SG, charge them up with a separate battery charger, put them under a load for a period of time and then check their voltage/amps (not hooked up to shore power).
You might also want to check the manual for your converter to see what, if any, stages it undergoes while charging your batteries.

Note to rkymtman: I also have the same TV and was unaware that a 30A fuse needs to be placed in Stud#1 position in order for the TV to charge the RV batteries. Will have to check my TV fuse box to see if there is a shunt or a fuse. Tks for the heads up.

[SAABDOCTOR]

HI THERE. NEED MORE INFO.... THEY CHARGE FINE ON SHORE POWER? WHAT IS THE VOLTAGE ON SHORE POWER? ALSO WHAT IS THE TOW /CAR/TRUCK. AND THE PIN CONFIGURATION? 4 PIN YOU WILL NOT GET ENOUGH CURRENT FLOW TO CHARGE TWO BATTERIES. ALSO ANY OF THE CORROTION ON OR IN THE CABLES? THAT WILL IMPEED CHARGING ESP AT A LOW CURRENT LEVEL... IF YOU CAN BORROW AN AMP METER AND MESURE THAT IT WOULD BE OF GREAT VALUE. WILL CHECK BACK OR CONTACT ME WITH A PM AT ANY TIME BARNEY

[hankpage]

Originally Posted by rcorkum4

Recently I've noticed that the coach batteries on our Sprinter 250RBS trailer are not charging when being towed. I left Portland, OR with batteries (2 x 6v golf cart batteries in series) at 1/2 charge and drove about 3 hours. Checked the batteries on arrival and found them still at 1/2 charge. I disconnected the + battery cable at the coach battery and measured about 13.6 volts across the battery cable and the chassis ground on the trailer with the TV running. I don't have an ammeter so am not able to see how much juice is flowing.

Any suggestions for trouble shooting further?

They charge just fine when connected to shore power.

Ron

With no load (Battery cable + disconnected)13.6v is normal output for your Toyota's alternator. The voltage should increase under the load of the low trailer batteries. Check the trailer plug for corrosion and TV plug also.

[rcorkum4]

I've been doing some calculations and found that my problem may be that the battery indicator is not sensitive enough to give a good diagnostic reading. I have 2 6v batteries with a total of 260 amp hours capacity. I measured the draw with the TT in towing mode and found that it draws about 1.2 amps. The wires in the 7 pin connector appear to be 12 gauge so, theoretically, I could be getting as much as 20 amps from the tow vehicle. The net max current to the battery is 18.8 amps x 3 hours of towing equals an increase of 56.4 amp hours which is roughly 20% of capacity. Since my battery level meter reads 1/4; 1/2; 3/4; Full, I may not have tipped the indicator to the 3/4 mark after 3 hours of towing.

I am currently unplugged from shore power an will wait until the battery indicator is down to 1/2. Since my ammeter is only good to 10 A and I cannot justify buying a new multi-meter just for this, I think that I'll go to an auto parts store and purchase -30 to +30 ammeter and wire it in next to my converter. This way I'll be able to monitor draw/charging in real time.

I'll post another update once I get the ammeter installed and have the batteries drawn low enough to get a valid reading during charging.

Ron

[hankaye]

rcorkum4, Howdy;

You've never told us what you have for a tow vehical.
Me, I have a 2004 F-250, my fuses are under the dash, have a 30 amp'er that was blown and I wasn't aware of it till I started pokin' around with a multi-meter. Once I replaced it my batteries charged up in very short order.

hankaye

[photolab]

Hank, you might also check the fuse and relay box under the hood, on the left inner fender, just behind the battery (assuming you have a diesel) There is one of the square top maxi fuses there for the RV battery charging system. As I recall, it is a 40 amp.

Generally, it is practical to tell a lot about battery state of charge and if it is charging or not by using a volt meter. This is what most monitor panel meters are, however they are usually wired in such a manner that when plugged in, they read the converter output, which is about no help at all for diagnostics.

Also, a normal battery will accept a charge at a rate limited by the present state of charge, with the charging device output being the upper limiting factor. Good luck, it sounds like you're on the right track! Anything having to do with electrical or A/C I'm there!