Problems with Charge Line

[don_kleinschnitz]

I have been installing the wiring and such to pull a 2018 Wrangler Sport.
All good until I got to the "charge line" that is needed to charge the Jeep battery.

With the RV running there is 14 VDC measured at the open end of the wire at the Jeep's battery. That is after it routes through the 7-pin, coil cord, and 6-pin connector, and up to the jeep's battery. So it seems the circuit is good.

When I connect the "charge line" to the TOAD's battery terminal that point drops to match the TOADS battery voltage i.e. 12.3 VDC vs the RV's 14 VDC charge level. This suggests the charge line is not providing charge current to the toad's battery.

Has anyone seen this kind of problem?
Does anyone know where the "charge line" originates? I.E. the fuse and relay?

Jayco refuses to provide any documentation on Ford wiring in the frame and the CAB.

Thanks for any help you can provide....
Don

 

[Grumpy]

If you have 14 v before connecting to the battery there would not be a problem with the MH wiring. Do you have a direct ground connection to the toad battery from the 6 pin as well as the charge line?

 

[don_kleinschnitz]

Yes, there is good ground from the RV to the toad. I measured the resistance and the voltage reference to the toad and the RV, and they are both good.

The strange thing is when I connect it to the toad's battery it goes to 12.3 v yet the RV's charging voltage stays at 14 VDC.

I have digital voltmeters in both the toad and the RV. The RV is charging and the Toad never sees that charge voltage when I connect the charge line to it.

It's as if as soon as current is drawn something opens the circuit.

 

[Grumpy]

Do you have an auto reset breaker in the FORD fuse box? Maybe it's tripping.

EDIT: Hook it up and see if the 14v returns, maybe you're getting a surge that is tripping the breaker and it needs to reset. Once it is connected it may not surge when you start the MH.

 

[Bullitt6283]

Have you kept the charge line connected to the Jeep battery to see if the voltage rises over time?

I suspect that the Jeep battery IS being charged, but the amperage it is pulling through the charge line wiring is high enough that you're seeing a voltage drop through the wiring. The return path wiring (ground) also contributes to the voltage drop.

Fuse #63 in the battery junction box is 30 amps, and the relay is in position #4. (2016 Ford E-450)
.

 

[don_kleinschnitz]

Body Builders Information

I was unaware of the availability of this information so I am sharing it. Quite useful. When asking Jayco where the source of the charge line was they could not, would not, provide nor even acknowledge it exists .

Found and verified the charge line circuit which uses the fuses/relay sited above.

https://www.fordbbas.com/vehicle-info/E-Series

 

[don_kleinschnitz]

Have you kept the charge line connected to the Jeep battery to see if the voltage rises over time?

I suspect that the Jeep battery IS being charged, but the amperage it is pulling through the charge line wiring is high enough that you're seeing a voltage drop through the wiring. The return path wiring (ground) also contributes to the voltage drop.

Fuse #63 in the battery junction box is 30 amps, and the relay is in position #4. (2016 Ford E-450)
.

Ya, I have been thinking something like that or a ground loop is what is going on.

I have not done this for any length of time as the RV has to be running.

But how can the toad battery be charging if the terminal voltage is 12.3???

I would expect that you would see the battery terminal voltage = the charging source just like a battery charger would.

I also put an ammeter in series with the charge line and it reads only a very small current when connected to the battery.

 

[Bullitt6283]

Have you kept the charge line connected to the Jeep battery to see if the voltage rises over time?
I suspect that the Jeep battery IS being charged, but the amperage it is pulling through the charge line wiring is high enough that you're seeing a voltage drop through the wiring. The return path wiring (ground) also contributes to the voltage drop.
Fuse #63 in the battery junction box is 30 amps, and the relay is in position #4. (2016 Ford E-450)
.

Ya, I have been thinking something like that or a ground loop is what is going on.
I have not done this for any length of time as the RV has to be running.
But how can the toad battery be charging if the terminal voltage is 12.3???
I would expect that you would see the battery terminal voltage = the charging source just like a battery charger would.
I also put an ammeter in series with the charge line and it reads only a very small current when connected to the battery.

Voltage drop is a function of current flow through a resistance. If current is flowing (battery is being charged plus any parasitic draws in the Jeep) you would not necessarily see the charging source voltage at the Jeep battery if there is voltage drop in the charge line. Voltage drop can be caused by the size and length of the feeder, as well as the quality of connections in the line (7-way connectors, umbilical cord plugs & sockets).
The charge line wire size or a connection somewhere along the line may be limiting the current flow. Taking a piece of 12 gauge wire and jumpering across at various points may tell the tale.

.

 

[don_kleinschnitz]

Thanks for hanging with me on this thinking..... while I'm waiting to do some more testing when the RV is available.

Here is what is challenging me:

The RV end of the charge line is at 14v and when connected to the toad battery the other end is 12v.
Assuming: the circuit is not open and drawing current there would be 2V dropped across some resistance.

The wire from the fuse to the 7-pin connector is a 35ft long #10 wire.

35 ft of #10 wire = .035 ohms.

Then I=E/R = 2/.035 = 57 amps

If the circuit was closed and charging the battery there would be 57 amps flowing and the fuse(63) would blow at 30 amps.

If it were normal for there to be 2v dropped across the harness resistance the fuse would always blow.

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It seems that somehow the circuit must be opened when the charge line is connected, which does not make sense.

or:

There is substantially more resistance than the harness (.035 ohms) somewhere.

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I will take on your suggestion of looking for drops in the interconnects but it would seem that the resistance would have to be substantial.

Now my head hurts....

 

[Ann-Marie]

It is working 100% normally. As a manufacturer of marine battery systems for over 30 years this is a common situation.
The charging current going in is the voltage difference between the batteries divided by the resistance of all the wiring.
The voltage drop through the wiring does not prevent a full charge. As the battery on charge charges to the source voltage the current drops to nearly zero (plus any loads). With zero current there is zero voltage drop in the resistance.

 

[Retired mountain folk]

Ours had no charge power coming thru all of a sudden, when our son problem solved he found out the ground at the plug was not good after fixing, all was good…..