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Old 01-05-2006, 10:20 PM   #1
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Battery Charging Idea?

I understand why my truck does such a poor job of charging my trailer batteries and want to do something about it.

My idea was to run battery cable from my alternator directly to my trailer batteries. Can anyone think of a viable reason NOT to do this?
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Old 01-05-2006, 10:42 PM   #2
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Steve, I mounted a battery isolator in my powerstroke. Its mounted on a seperate bracket, but attached to the alternator bracket. Helps it stay some what cooled the same way the alternator is cooled, by the passing air from the radiator fan. Mine is rated for 150 amps, with the primary terminal side connected to the charge line, for the truck batteries, and the secondary terminal connected to the trailer batteries. I can't remember the gauge of wire I installed and ran back through the truck, but completely seperate from any Ford intigrated charging wire. You will need an isolator equal to your alternators amperage output,( I toasted a few 100 amp models prior) plus you need the isolation from your truck batteries, or you will find that you draw current from them, when your connected to your trailer, and your truck is not running. Jeff
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Old 01-05-2006, 11:40 PM   #3
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Quote:
Originally Posted by Coastalview
You will need an isolator equal to your alternators amperage output,( I toasted a few 100 amp models prior) plus you need the isolation from your truck batteries, or you will find that you draw current from them, when your connected to your trailer, and your truck is not running. Jeff
Jeff,

Why do I need an isolator at all? I'm planning to use 175 amp Anderson connectors between the truck and trailer. All I need to do is pull the plug should I leave the truck connected to the trailer while using the trailer.
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Old 01-06-2006, 05:39 AM   #4
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Does anything stick...

Quote:
Originally Posted by Steve Heywood
I understand why my truck does such a poor job of charging my trailer batteries and want to do something about it...
Steve,

Typo? Do you understand? If so, what is the reason?

While I know no details about your particular situation, allow me to throw a few things out: Perhaps your batteries are drawing too much current, and your Tow Vehicle's circuit breaker keeps popping & resetting. Or maybe the TV has yet another computer controlling the amount of current the charge wire is allowed to have. Maybe your truck has a wimpy alternator (either wrong one installed or its going bad). Lastly, maybe there's a problem with your trailer connector wiring.

Or maybe the truck just needs your idea implemented.

I see nothing wrong with your idea's premise, but it would seem to me that your truck would have been wired the best way from the factory.

Good luck,
Tom
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Old 01-06-2006, 06:20 AM   #5
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Think you need a truck alternator with more capability, if you are unsatified with the current performance. Alternative alternators are available for most trucks. ie: ones designed for emergancy vehcile use. Have you monitored the amps drawn by charging your camper batteries or the voltage at the batteries and at the alternator during charging? That is the only way to see if the wire leading from the alternator to the batteries in the camper are adequetely sized.
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Old 01-06-2006, 07:18 AM   #6
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Steve, you can directly in line wire your charge line to the trailer. But consider that your alternator will be attempting to charge 4 batteries at once. The isolater will direct charging current to the truck batteries first, and when up to a full recharged status, it will then direct the charge curcuit to the secondary charging circuit, and that being your charge line to your trailer batteries. I like the idea of not opening the hood every time I stop, and isolates my truck from my trailer, thus no fuss being fully automated.
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Old 01-06-2006, 09:55 AM   #7
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The best idea I have seen for improving battery charging via the tow vehicle is a boost controller. In most cases, an extra twenty amps from the tow vehicle charging system is not a problem. The problem is that it doesn't (and can't if it is to do its primary job) supply the voltage needed to get that 20a back to the trailer battery.

With modern electronics, a boost controller isn't that expensive and they are fairly efficient. There was a 'build your own' article in QST recently. The MPPT type solar controllers are another example. I have seen some commercially (sorry, no link to hand) but I haven't seen any coupled with an intelligent 3 stage battery charger.

One way to approach this would be to put a kilowatt inverter up front (probably in cabin) connected to a house battery in the tow vehicle that was properly isolated from the engine battery. Then run 110v back to the trailer to a smart charger on the trailer battery. This would probably run the efficiency down to 70% - 80% and need a bit of care in its use but there would be some other advantages as well.
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Old 01-06-2006, 10:21 AM   #8
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Quote:
Originally Posted by Steve Heywood
...My idea was to run battery cable from my alternator directly to my trailer batteries. Can anyone think of a viable reason NOT to do this?

Steve:

Two reasons NOT to do it -

1.) Battery Cable MAY or MAY NOT be the proper sized wire. Follow the link below, and run the numbers in the calculator through a couple of times with the range of amps you intend to transmit to the trailer batteries - be sure to use an accurate length for the wire (all of the turns and ups and downs add up), add a few feet for connector inefficiencies. You'd be surprised at the voltage drop in even 4 gauge wire when you get over 30 amps. Don't forget to factor in the voltage drop in the (probably smaller) wire from the tow vehicle umbilical connection to the trailer battery.

http://www.powerstream.com/Wire_Size.htm

2.)Be sure to include a fuse or breaker in the circuit. you could well fry the alternator if the circuit is not protected from a dead short.
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Old 01-06-2006, 10:26 AM   #9
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Quote:
Originally Posted by TomW
Steve,

Typo? Do you understand? If so, what is the reason?

While I know no details about your particular situation, allow me to throw a few things out: Perhaps your batteries are drawing too much current, and your Tow Vehicle's circuit breaker keeps popping & resetting. Or maybe the TV has yet another computer controlling the amount of current the charge wire is allowed to have. Maybe your truck has a wimpy alternator (either wrong one installed or its going bad). Lastly, maybe there's a problem with your trailer connector wiring.

Or maybe the truck just needs your idea implemented.

I see nothing wrong with your idea's premise, but it would seem to me that your truck would have been wired the best way from the factory.

Good luck,
Tom
I learned (the hard way-I used to haul a slide-in camper on a diesel powered SD truck) that as configured from the factory a Ford Super Duty pickup equipped with a Powerstroke diesel and a single 110 amp alternator will never fully charge any "extra" batteries. Ford equipes these trucks with a relay that automatically isolates the truck from the "RV" charging circuit whenever the engine is not running. The truck's voltage requlator gives preference to the two starting batteries when you first start the truck. Even after the two truck batteries are fully charged the amount of current available at the end of 30' (plus) of #12 wire is not enough to make a significant dent in the charging requirements of 2 group 27 (or larger) deep-cycle batteries. It takes over 48 hours for my home battery charger to fully recharge my 2 GP 27 trailer batteries at the end of a 2 day camping trip, and that's after a 3 hour drive home from the campground.

My idea is as follows: Run a #4 battery cable from the charge post of my alternator through a switchable 120 amp circuit breaker to the rear of my truck where it will terminate at a 175 amp Anderson quick disconnect plug. On my trailer I will run #4 battery cables forward from the batteries to another Anderson plug. While not perfect this settup will significantly reduce the voltage drop seen at the trailer batteries and will allow me to simply add another deep cycle battery to the trailer (something I do now while dry camping) using yet another Anderson connector. The switchable circuit breaker will allow me to isolate the truck from the trailer while stopped.
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Old 01-06-2006, 12:40 PM   #10
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Steve, been thinking, could you add a solenoid to make your idea automated?
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Old 01-06-2006, 02:42 PM   #11
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Risk mitigation

Steve,

The relay that automatically isolates the truck from the RV charging circuit is a good thing. None of the batteries will charge unless the engine is running, and the relay will keep your trailer batteries from draining your starting batteries if the trailer batteries are seriously depleted. Although there may be a voltage drop associated with the relay, the relay’s function is a good thing.

I’m struggling a bit with the truck’s electronics giving preference to the starting batteries. I do not know about Fords, but on GMs, the voltage regulator is built in to the alternator. Although it is entirely possible that both manufacturers have a separate “power to everything else” regulator, in normal operation, I would not think it would take long to “top off” the starting batteries once you are on the road. Why bother to limit the current to everything else?

12 gauge wire does sound a little small to safely accomplish your goals. But if it is a serious bottleneck to charging your trailer batteries, I would think it would be getting a bit warm perhaps even melting your umbilical connector pin a bit. 4 gauge wire certainly sounds up to the task. “Overkill” comes to mind though - That size wire will be tough to route.

Let’s say you implement your idea. If you are reasonably sure that the existing charge wire’s circuit breaker has not been constantly resetting, my gut feeling is that you may be disappointed with the results. While your alternator may be rated to deliver 110 amps, it will only do that at a maximum of 14.7 volts or so. Charging batteries fast requires 16 volts or more. The bottom line is that you may do all that work, and, after hanging an ammeter on the alternator’s output, find that the alternator is still only delivering 85% of it’s rated current, and the trailer batteries do not charge much if any faster.

So what is the solution? I don’t know; Maybe a combination of bigger alternator & thicker charge line wire. But if you have confidence in your current strategy, perhaps some risk mitigation would save you some bucks.

Since the present issues include “distance to alternator” & “is the charge wire thick enough”, how about, as a test, moving the batteries closer, and hooking them to the charging system with better-than-12-gauge wire? For example, put them in the front floorboard, and wire them with 8 gauge?

Good luck whatever you do,
Tom
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Old 01-06-2006, 03:02 PM   #12
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Quote:
Originally Posted by Coastalview
Steve, been thinking, could you add a solenoid to make your idea automated?
I hadn't thought of a solenoid. Since I need a circuit breaker I was planning to use a switchable one and simply open the hood in order to manually trip or reset the breaker as needed.
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Old 01-06-2006, 03:23 PM   #13
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Quote:
Originally Posted by TomW
I’m struggling a bit with the truck’s electronics giving preference to the starting batteries. I do not know about Fords, but on GMs, the voltage regulator is built in to the alternator. Although it is entirely possible that both manufacturers have a separate “power to everything else” regulator, in normal operation, I would not think it would take long to “top off” the starting batteries once you are on the road. Why bother to limit the current to everything else?

12 gauge wire does sound a little small to safely accomplish your goals. But if it is a serious bottleneck to charging your trailer batteries, I would think it would be getting a bit warm perhaps even melting your umbilical connector pin a bit. 4 gauge wire certainly sounds up to the task. “Overkill” comes to mind though - That size wire will be tough to route.

Let’s say you implement your idea. If you are reasonably sure that the existing charge wire’s circuit breaker has not been constantly resetting, my gut feeling is that you may be disappointed with the results. While your alternator may be rated to deliver 110 amps, it will only do that at a maximum of 14.7 volts or so. Charging batteries fast requires 16 volts or more. The bottom line is that you may do all that work, and, after hanging an ammeter on the alternator’s output, find that the alternator is still only delivering 85% of it’s rated current, and the trailer batteries do not charge much if any faster.
12 ga wire is what Ford uses for the charge line in their trailer wiring harness.

I based my conclusion on the fact that my camper hauling truck provided almost no extra juice to the camper right after I started the truck and the camper battery was nearly dead. What probably happened was the power from the alternator was taking the path of least resistance and because of the 12 ga charge wire and the demand I was placing on it (4 electric camper jacks) I wrongly assumed the truck was protecting itself.

I was going to use 4 ga wire for a couple of reasons. I found some for just over $1.00 a foot with no minimum and that's the smallest wire you can use in a 175 amp Anderson connector. Routing it out of my engine compartment along the frame to the rear bumper won't be that difficult.

I realize that I may do this and realize minimal gains. However, it's only going to cost around $100 and nothing else I can do for the money will make things better. I see no downside (other than cost) to my plans and should I decide to upgrade to a second alternator (a Ford factory option) the wiring will already be installed.
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Old 08-03-2006, 01:37 PM   #14
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Steve,

Any updates?
did you end up running the 4 Gauge wire?
How does it work?

Steve
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