DC to DC charger vs 7 pin

Boatmonkey

Observer
I'm putting a battery and charging system together for my trailer. My question is what's the difference between DC to DC charger vs 7 pin for charging the batteries? Is it just a matter of faster charging through the Dc to DC or....? Thanks.
 

DiploStrat

Expedition Leader
Wow! At the risk of being snarky, if you don't know, then you need to find some good electrical help or start doing some reading. (A small start: https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf)

Basically:

-- The wiring on most 7 pin plugs is too small to carry many amps. This will result in a slow charge and, if you don't drive long enough (and you won't) an incomplete charge - kiss of death for lead acid.
-- A battery to battery charger still needs a large cable, probably larger than what you 7 pin has,
-- A battery to battery charger can compensate for small voltage drops. More to the point, its charging profile is probably a better match for your battery than the profile of your vehicle's charging system. (Especially if you have a newer vehicle.)
-- Most battery to battery chargers incorporate proper isolation to keep a dead camper battery from draining your vehicle battery.

All of the above grossly over simplified, but, I believe correct.

Hope this is helpful.
 

Buddha.

Finally in expo white.
If your alternator has you at 13v and you’re trying to charge through 20’ of 10-12 gauge wire your trailer battery isn’t getting enough voltage to actually charge.

Running a heavier wire would help, less voltage drop.

The dc to dc makes up for voltage drop, and usually incorporates a heavier wire.
 

dfinn

Adventurer
It’s actually amps that would be limited by wire thickness. Voltage would stay the same until current increases and at that point it would drop.

that said, charging via the 7 pin vs a dc to dc charger are 2 very different things. It sounds like you need the dc to dc.
 

Boatmonkey

Observer
Wow! At the risk of being snarky, if you don't know, then you need to find some good electrical help or start doing some reading. (A small start: https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf)

Basically:

-- The wiring on most 7 pin plugs is too small to carry many amps. This will result in a slow charge and, if you don't drive long enough (and you won't) an incomplete charge - kiss of death for lead acid.
-- A battery to battery charger still needs a large cable, probably larger than what you 7 pin has,
-- A battery to battery charger can compensate for small voltage drops. More to the point, its charging profile is probably a better match for your battery than the profile of your vehicle's charging system. (Especially if you have a newer vehicle.)
-- Most battery to battery chargers incorporate proper isolation to keep a dead camper battery from draining your vehicle battery.

All of the above grossly over simplified, but, I believe correct.

Hope this is helpful.
Well, you did come off as snarky. Not sure why you think you need to tell me I need to find some good electrical help when you have no idea what I know. I have wired two separate sailboats up to ABYC standards previously. I simply asked about one piece of equipment that I was unfamiliar with, here, where people would have the answer. I got some helpful advice and then I got you....my lucky day.
 

DiploStrat

Expedition Leader
Well, you did come off as snarky. Not sure why you think you need to tell me I need to find some good electrical help when you have no idea what I know. I have wired two separate sailboats up to ABYC standards previously. I simply asked about one piece of equipment that I was unfamiliar with, here, where people would have the answer. I got some helpful advice and then I got you....my lucky day.
It was never my intention to give offense. Please take another look at your question. You offered no information or background, and thus you are quite correct - I had no way of knowing what you know. Your question is not what I would expect from someone who has wired two boats.

My apologies, but when someone asks an extremely basic question, there is always the danger that a simple answer will be taken out of context. For example, you did not tell us the charging profile of your vehicle, nor the type/size of battery, nor the system of isolation you are using, if any. All of these would change the answer.

Please consider my reply - I went to great length to be sure that the information offered was correct in any context. I certainly did not blow you off.

And again, I hope that the answer I gave was complete and correct.
 
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firewhite

firewhite
Most newer vehicles have a smart alternator. What that means is the ECM controls the alternator as load demand for the vehicles main battery is needed or not, off or on. Therefore your trailer battery may never really get much of any recharging from vehicle alternator. I have a Redarc BC to DC controller on my trailer. It charges my trailer battery at 25 amps if needed while driving and also works as a solar controller for my panels when camping.
 

DiploStrat

Expedition Leader
News you can use?

-- A major drawback with some (most) factory wired 7 pin connectors is that the gauge of the wire is probably too small (i.e. gauge too small) to pass enough amps to charge a camper battery during the time that the vehicle is running. This is especially a problem with lead acid where getting a full charge is essential to long battery life.

-- A second issue is that the charging profile of your vehicle may not be appropriate for your camper battery. The new "smart" alternators increase the chances of this. A DC-DC charger can fix this problem.

-- Sadly, because of the question of wire gauge, simply mounting a DC-DC charger on your tailer and plugging it into the 7 pin connector may not work because of the wire gauge and length. But, a small enough battery and a short enough run and you may be fine. You need to check the documentation of your DC-DC charger. (I use REDARC and they generally want a minimum of 6 AWG.)

Again, hope this is helpful.
 

robtbritn

New member
I would just plan on running 6AWG wire with inline circuit breaker to the back of your vehicle with Anderson plug at rear bumper. On the trailer side DC-DC charger with Anderson plug to front of trailer. Use your 7 pine connector to handle trailer lights / brakes and the Anderson plug for charging duties.

Bob Britton
Hollister, Ca
 

DiploStrat

Expedition Leader
I would just plan on running 6AWG wire with inline circuit breaker to the back of your vehicle with Anderson plug at rear bumper. On the trailer side DC-DC charger with Anderson plug to front of trailer. Use your 7 pine connector to handle trailer lights / brakes and the Anderson plug for charging duties.

Bob Britton
Hollister, Ca
Some of us would argue for a larger wire, depending on the battery bank, etc. I used a pair of 0 AWG cables, but, doing it over, would have used a single 0 AWG. But that was a 600+ Ah battery, about 25 feet from the alternator.
 

Alloy

Well-known member
A
News you can use?

-- A major drawback with some (most) factory wired 7 pin connectors is that the gauge of the wire is probably too small (i.e. gauge too small) to pass enough amps to charge a camper battery during the time that the vehicle is running. This is especially a problem with lead acid where getting a full charge is essential to long battery life.

-- A second issue is that the charging profile of your vehicle may not be appropriate for your camper battery. The new "smart" alternators increase the chances of this. A DC-DC charger can fix this problem.

-- Sadly, because of the question of wire gauge, simply mounting a DC-DC charger on your tailer and plugging it into the 7 pin connector may not work because of the wire gauge and length. But, a small enough battery and a short enough run and you may be fine. You need to check the documentation of your DC-DC charger. (I use REDARC and they generally want a minimum of 6 AWG.)

Again, hope this is helpful.
An issue with computerized vehicles is that if the vehicle does not detect the trailer it may turn off the charging.
I installed LED lights on my trailer.
A month later I was getting "Trailer Disconnected" while driving then it would switch to "Trailer Connected".
FORD doesn't/won't provide any information on thier system even to FORD techs so it took forever to troubleshoot.
Ended up using a blocking plug. When the blocking plug is used the truck gives a "Trailer Disconnected" but everthing works.

I'll add one thing for anyone reading this is to make sure the battery supplying power to the (emergency breakaway) brakes is charging.
 
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