Does 7 pin charging go both ways?

[RiverRatMatt]

I know that my camper can take charge from the 7 pin from the tow vehicle, but the camper has 100 watts of solar built in so my bigger concern is the tow vehicle's battery. I've searched around and can't find the answer: can the camper charge my tow vehicle through the 7 pin connector?

 

[ntsqd]

That depends on what you battery separator is. If you are using a bi-directional Voltage Sensing Relay then the solar can charge the TR battery(ies). If you're using a single directional or some for of keyed signal solenoid, then no, it can not.

Kind of a moot point. Given the length of the wire run and it's puny size (10ga. connector limitation) you aren't going to get much more than just at rickle charge anyway.

 

[LC4LIFE]

Yes it can. I have mine wired so all the batteries can be charged while driving via the rig, or while parked via the solar on my teardrop. I run a BlueSea 7610 ACR and dual batteries in the truck and a deep cycle on the tongue of my teardrop. Everything works wonderfully. I did however, make sure have large enough wire running everywhere so there is no voltage drop. I feel like it's overkill, but I also have tremendous peace of mind.

 

[ntsqd]

Voltage Drop Look-up Chart:

Ancor

For over 40 years, Ancor has been the market leader in Marine Grade® wire and wire management tools. All of our products are built for the harsh marine environment and conform to industry standards.

www.ancorproducts.com

Note that the circuit length must include the ground path length too. If you are charging a battery then the charging voltage must be greater than the 100% SoC voltage for that battery. I like at least a full volt greater. The closer the charging voltage is to the battery voltage the slower the charge rate will be.

Example: Say that the batteries are 15 feet apart, that makes it a 30 foot circuit length (hot + ground lengths). If you use the 7 pin connector you are limited to a 10ga. wire, max. By that chart the maximum amperage is 10 amps. If the charging voltage is 13.6 volts at the source, then with that 3% voltage drop the voltage at the far battery will be 13.2 volts. If the 100% SoC resting voltage for that battery is 12.6 volts then you're charging with less than a one volt difference. Not good; will work, but not good as you probably will not get that full 10 amps.

 

[LC4LIFE]

Voltage Drop Look-up Chart:

Ancor

For over 40 years, Ancor has been the market leader in Marine Grade® wire and wire management tools. All of our products are built for the harsh marine environment and conform to industry standards.

www.ancorproducts.com

Note that the circuit length must include the ground path length too. If you are charging a battery then the charging voltage must be greater than the 100% SoC voltage for that battery. I like at least a full volt greater. The closer the charging voltage is to the battery voltage the slower the charge rate will be.

Example: Say that the batteries are 15 feet apart, that makes it a 30 foot circuit length (hot + ground lengths). If you use the 7 pin connector you are limited to a 10ga. wire, max. By that chart the maximum amperage is 10 amps. If the charging voltage is 13.6 volts at the source, then with that 3% voltage drop the voltage at the far battery will be 13.2 volts. If the 100% SoC resting voltage for that battery is 12.6 volts then you're charging with less than a one volt difference. Not good; will work, but not good as you probably will not get that full 10 amps.

Agreed. You have got to think about it all for sure. I mitigated the 10ga a bit by only using it inside the 7pin run between the trailer battery and the back of the truck for probably only 6-7ft. Beyond that its either 2awg or 4awg depending on where you look. I also regularly see 14ish volts or so from my alternator at the back of my truck and out of the solar controller in the trailer. Its been working great, but @ntsqd makes very good points.

 

[ntsqd]

Particularly with mobile Solar systems you frequently will see really heavy wire gauges used. It is not because of large current. It is keeping the voltage drop to the barest minimum.

 

[e9999]

and even with a small wire, the towed battery can do weird things with the vehicle electronic systems. Like in some 100s, as discussed here.

 

[LC4LIFE]

and even with a small wire, the towed battery can do weird things with the vehicle electronic systems. Like in some 100s, as discussed here.

Do you have a link or can you point me to more info? I may have a 100 or 200 one of these days so I'd like to know more.

 

[e9999]

that was a thread I started some years back, maybe 6 or 7, where I reported on some weird feed back into the dashboard. Try the likely keywords, as in this discussion.