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Old 02-11-2019, 12:40 AM   #43
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Quote:
Originally Posted by Lstyles View Post
In an RV you can easily use your alternator to charge the batteries as the wire run would be short. However, it would seem to be much more difficult to use the Tow vehicle alternator to charge a travel trailer. I understand that you might get some trickle charge across the wiring harness set up for trailer lights but the gauge would be way too small to get much. Do people fashion thick gauge wire/cable across the hitch point to try and charge the trailer battery? It seems like that would be risky.
Thoughts?
The 7-wire trailer plug has a B+ that you run a FUSED/ protected wire by RELAY (IGN controlled) from tow battery to harness, and also FUSE/ protect on TT battery end. Suspect #10 (30a) wire? e-TRAILER SAYS min #12
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Old 02-11-2019, 06:48 AM   #44
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There are a lot of variables, but here’s my story.

I have a residential refrigerator, and want it running while traveling using my 2019 F350 DRW with dual extra heavy duty alternators to pull my 5er.

My fridge says 1.75a * 115v on the sticker. I have a 1000w inverter and was delivered one, garbage, Interstate Marine, 88 ah battery.

The idiot battery lights would show full at hookup and near empty 8 hours later using only the 7 way.

After complaining to the dealer, they apologized and installed a second, garbage battery. The result is to be expected, somewhere between 1/3 and 2/3 at destination.

However, the point is to not draw them down — both for cycle life AND so I unhitch at the destination with full batteries.

That led me to create a thread on the Ford trucks forum which began a three month long electrical redesign.

I, also, found the video above, and decided to run #2 AWG wire from the battery to the bed of my truck. I also ran the same wire along the pigtail and into the front bay of my coach. I connected it to a REDARC BCDC1240D — wishing I could have got the 50 amp version, but could not find it for sale in the US at the time.

At the time of installation, I also installed a Victron battery monitor.

What I learned, was when the fridge was running most of the time it was pulling up out 18 to 19 A from the batteries to power the inverter.

With the 7 way plugged in, and all the black magic stars aligned, the pigtail was supplying about 14 A to offset the drain. Also, I measured >14v off the alternator, but have not put any effort into measuring how often that is the case.

The reason I say black magic, is I have learned the pigtail only charges when it sees fit. There are weird algorithms about whether or not you have moved the gear selector from park, or are stepping on the brake, or have remote started or not, … It turns out many times I assumed it was charging, and it was not.

Also, with all the computerization under the hood, I’ve been told… However have not experienced… The voltage fluctuates wildly based on several factors. I think the reason I don’t experience it, is when you’re pulling hard on the batteries, the alternators are charging at peak charge.

Where it also gets tricky, is when the voltage comes up to some number… I don’t know why… They will shut off, rather than do absorption and float charging… Or so the story goes.

But long story short, with out the additional charging system, I had unacceptable results. Imagine getting caught in a Walmart parking lot overnight, and having to run the generator just to keep your food cold while you sleep for 6 to 8 hours.

With my additional charging system, wherever I go, I get there with fully topped off batteries.

However, with only those two batteries the dealer installed, and much more electrical hocus pocus, related to how fast you’re drawing down the batteries, even then I was only able to run the residential refrigerator or 5 to 6 hours before hitting the magic 50% number, not to be exceeded according to many Internet and battery experts.

Worse, starting the trip from that perspective, there was just not enough juice from the 7 way pigtail to recharge the batteries, and keep the fridge running.

So I upgraded to first four, then six, 100 amp hour AGM batteries. Much more hocus-pocus suggests 6 V batteries would’ve been a better choice, but more hocus-pocus suggests there are problems running inverters and residential fridge off of them. At the end of the day, I took a shortcut on that learning, and just used the 12 V batteries.

What I really wanted was lithium, but I figured first they’re too expensive after all the other changes that I’m making, and second I need to learn how to manage the batteries that I have, so I don’t ruin the expensive ones.

But now, I have power for days. As long as I don’t try to run the AC, my refrigerator is happy for as long as I’ll ever want it and to be. And where I go I end up fully charged batteries, although now the DC to DC charger is not enough to charge everything if I draw them all the way down — so now I’m considering putting a second one in parallel.

However, more hocus-pocus as the manufacturer says you should not use solar if you have them in parallel, and I’ve already bought 1000 W of panels as my next project. So that means either I can’t use their cool MPPT that’s built-in, and have to have a separate solar controller, or I have to figure out that hocus-pocus.

All of this to say, the seven way pigtail is enough for people without residential refrigerators who rarely if ever Boondock. However, if you draw down your battery hard, it will not keep up… At least in my truck.
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Old 02-11-2019, 06:57 AM   #45
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Originally Posted by SV Tom View Post
If the 12 volt outlets on generators that have cables with battery connectors on them are not meant for charging batteries what are the meant for ?
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Originally Posted by twinboat View Post
They can charge batteries but at only 8 amps. You will need to run the generator for 8 to 10 hours to charge a lightly discharged battery bank. Then you need to worry about overcharging.
The bottom line is, the 12VDC output on most generators likely makes <13.0VDC. To charge a lead acid battery, you need an MINIMUM of 13.2VDC. High power chargers exceed 14.0VDC at least part of the time.

The main reason the 12VDC output is there is MARKETING ! That voltage is used internally for other purposes. Putting a non-standard 12VDC connector on the outside gives the advertising people another thing to brag about !
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Old 02-11-2019, 07:22 AM   #46
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Originally Posted by 191124x7 View Post
I have a residential refrigerator, and want it running while traveling using my 2019 F350 DRW with dual extra heavy duty alternators to pull my 5er.
.
.
.
... decided to run #2 AWG wire from the battery to the bed of my truck. I also ran the same wire along the pigtail and into the front bay of my coach. I connected it to a REDARC BCDC1240D — wishing I could have got the 50 amp version, but could not find it for sale in the US at the time.

At the time of installation, I also installed a Victron battery monitor.

What I learned, was when the fridge was running most of the time it was pulling up out 18 to 19 A from the batteries to power the inverter.

With the 7 way plugged in, and all the black magic stars aligned, the pigtail was supplying about 14 A to offset the drain.

The reason I say black magic, is I have learned the pigtail only charges when it sees fit. There are weird algorithms about whether or not you have moved the gear selector from park, or are stepping on the brake, or have remote started or not, … It turns out many times I assumed it was charging, and it was not.

Also, with all the computerization under the hood, I’ve been told… However have not experienced… The voltage fluctuates wildly based on several factors. I think the reason I don’t experience it, is when you’re pulling hard on the batteries, the alternators are charging at peak charge.
EXCELLENT FEEDBACK ! Thank you for telling us your story !

I am not familiar with the Victron battery monitor. Does it use a shunt to measure current flow in and out of your house battery bank ?

Modern (since about 2000MY) charging systems are OPTIMIZED to draw the minimum amount of power to recharge the vehicle battery. Algorithms are different between manufacturers and change year to year. Many companies now have additional senors to monitor the vehicle battery state of charge. Charging a trailer/house battery is an after thought.
  • I was surprised that the standard 7-way connector and wiring could not supply enough current to at least MAINTAIN the state of charge in the trailer ! This is the "black magic" !!
  • #2 AWG and a REDARC are (IMHO) overkill. The standard wiring should be able to provide whatever current the REDARC needs, at admittedly at <13.0V.
With the REDARC installed, I am very surprised that you were still losing charge on two 12V battery house bank after driving 5+ hours !

BTW, I concur with your other research. You would have happier with four 6VDC golf cart batteries. They will last longer than "marine" batteries. If you really want AGM, Trojan makes an AGM golf cart battery.


EDIT : FYI - A pair of Group 27M marine batteries will give you about 190 Ahr. A pair of GC2 golf cart batteries will give you about 220 Ahr. Flooded (wet) GC2 batteries cost less than flooded 27M batteries and a lot less than AGM Group 27M (obviously). I do know that AGM GC2 batteries are a lot more expensive than flooded GC2 and you would likely have to order them through a golf carts distributor.
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Old 02-11-2019, 09:34 AM   #47
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When I bought my last tow vehicle, back in 86, I ordered it with a tow package.
It came with a higher amp alternator, among other things.

If that wasn't for charging another battery what was it for ?

By design, motor home alternators charge house batteries all of the time.

A charge line is not going to wear out your alternator.
The bigger alternator is to keep up with the extra draw of the trailer, (lights, brakes, maintain breakaway battery).
Certainly a motorhome alternator will to some extent charge your coach batteries, but if you use very much power through the night, a days driving will not fully charge your/my coach batteries.
I believe that has something to do with the built-in regulator, once your chassis batteries are topped up, the alternator just idles.
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Old 02-11-2019, 09:59 AM   #48
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Using your alternator to charge your house batteries will result in cooked batteries. You should have an on board charger such as the latest technology from Progressive Dynamics which uses power from a 30A or 50A service. Underway or boondocking you can use solar panels or generator. House batteries are typically Deep Cycle, and require a much different charge rate then that provided by an alternator
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Old 02-11-2019, 10:05 AM   #49
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Motorhome alternators do not charge the house batteries. Chassis batteries only!
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Old 02-11-2019, 11:40 AM   #50
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Motorhome alternators do not charge the house batteries. Chassis batteries only!
That's not true, almost all MHs have a isolation system that links the chassis battery to the house battery.

That creates a large bank of batteries. When that happens, the higher voltage chassis batteries charge the lower voltage house batteries. Once the voltage of the chassis battery drops, the alternator raises its output and all batteries are charging.

In a few hours, the house batteries equalise with the chassis batteries.
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Old 02-11-2019, 01:01 PM   #51
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Generator 12v charging

Most of the smart chargers I've found are 2/10/20amp with 50amp for starting. Is this what is meant by 50 amp smart charger for TT battery charging instead of 12V plug on generator or am I looking at the wrong equip ?

Thanks
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Old 02-11-2019, 02:25 PM   #52
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That's a slick battery box they make. I'll check whether it works with both deep-cycle lead acid trailer batteries as well as lithium 12v's. Thanks for the info!
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Old 02-11-2019, 05:25 PM   #53
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EXCELLENT FEEDBACK ! you for telling us your story
This is the battery monitor I use. And yes to the shunt.

https://www.victronenergy.com/upload...0x_part1_2.pdf

While 2 awg may be overkill for one 40a charger, it will be just fine when I run a second BCDC and push 80a 35 feet back from the battery.

Thanks for the explanation about modern alternators.
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Old 02-12-2019, 08:50 AM   #54
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This is the battery monitor I use. And yes to the shunt.

https://www.victronenergy.com/upload...0x_part1_2.pdf
Looks like a nice unit ! Straight forward install.

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While it is interesting that you can use it to monitor your vehicle starting battery, I would not want to run the main ground wire from that battery to where the shunt is located (dotted line connection in picture).
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Old 02-12-2019, 09:01 AM   #55
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Most of the smart chargers I've found are 2/10/20amp with 50amp for starting. Is this what is meant by 50 amp smart charger for TT battery charging instead of 12V plug on generator or am I looking at the wrong equip ?

Thanks
You don't want a 50 amp boost type charger, although it will charge at 20 amp, but slowly.
You want a deep cycle battery 3 or 4 stage charger. Get one capable of 40 to 60 amps.
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Old 02-12-2019, 10:31 AM   #56
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I took apart a 12ga extension cord and used that to power my trailer brakes and charge line from the van. Both circuits get power directly from the battery, (with a relay so they are not connected when the key is off), and it has worked fine to keep my TT batteries topped off while driving (and ruining a small 120v beer fridge via an inverter). I also use 20amp breakers on both lines to protect from shorts.
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