Battery Charging

[AndyG]

The current thread about trailer winches has me wondering about charging a winch battery on the trailer from the truck. I want to mount my winch on the trailer with its own battery. I also want to slowly charge the winch battry while I drive with power from the truck. I have a accessory wire on my 6 pin connector already. The wire is currently being used to charge the small battery for the emergency brakes. My accessory wire is 12 or 14 Ga. I know that I can't simply run a hot wire to the winch battery because the battery will draw a bunch of current if it is low. High current = melted wire. How do a limit the current to allow trickle charging?

[Elden DuRand]

Originally Posted by AndyG

I also want to slowly charge the winch battry while I drive with power from the truck. I have a accessory wire on my 6 pin connector already. The wire is currently being used to charge the small battery for the emergency brakes. My accessory wire is 12 or 14 Ga. I know that I can't simply run a hot wire to the winch battery because the battery will draw a bunch of current if it is low. High current = melted wire. How do a limit the current to allow trickle charging?

Andy:

The easiest way to limit charging current is to use one or more brake light bulbs in parallel, the parallel connected lamps connected in series with the hot wire from your vehicle battery.

This does two things. One, it limits the maximum current drawn by the winch battery and, Two, the lamps will indicate when the winch battery is low. I'd limit the maximum charging current to about 5 amps.

Hope this helps

Take care - Elden
http://home.cybertron.com/~edurand

[Phillip Hutchinson]

[quote=Elden DuRand]Andy:


This does two things. One, it limits the maximum current drawn by the winch battery and, Two, the lamps will indicate when the winch battery is low. I'd limit the maximum charging current to about 5 amps.

G'Day
As I said in an ealier message: link your vehicle battery & Winch Battery using a 70 amp relay with a 40 cicuit breaker,this will limit the current,also fit a fusible link (out here in Aus a black link is rated at 30 amps continuous) at your winch battery this protects against a short circuit from the winch battery.
The relay is controlled from an ign or accessory feed (by using an acc feed it will automatically isolate your engine and winch batteries when starting your vehicle,I use a twin 6 mm cable to run the charge cable to the rear of the vehicle.If you want to carried away you can use an "Anderson "plug/socket same as used on electric forklifts and sweepers but in a smaller size.
As i am an Auto motive Electrical Technition by trade I have tried all sorts of methods and this works the best,I have probably set up 40 plus of these systems.There is a relay available out here that has a electronic module on it that senses the state of charge of the vehcle battery and only links the 2 together when the voltage rises to a set level,and drops out at a preset lower level,the company that makes it is called "Redarc".
As far as fitting globes in the charging cicuit this will limit the current flow but also it will restict the voltage at the winch battery therefore I believe it wont' fully charge,this has the same effect as using to smaller cable.
I hope that this info is not over the top. Also beware of any type of dual battery charging system that uses "Diodes" (same problem) I know some of you will say thats a lot of bunkum but i'm only telling you what I have found
Happy cranking Phillip

[Phillip Hutchinson]

Oops should have proof read the above before posting it sorry about the typo's

[Ralph Leonard]

Andy, if you are going to use a regular size auto battery, why do you want to charge it slow (trickle charge)?

Most travel trailers and motor homes use a isolator that allows charging the engine battery and coach battery at same rate, very simple and inexpensive setup. The line loss in a #12 wire lengh to the trailer will be sufficient to control current to trailer battery.

Any camper dealer can help you with this setup.

[AndyG]

Originally Posted by Ralph Leonard

Andy, if you are going to use a regular size auto battery, why do you want to charge it slow (trickle charge)?

Most travel trailers and motor homes use a isolator that allows charging the engine battery and coach battery at same rate, very simple and inexpensive setup. The line loss in a #12 wire lengh to the trailer will be sufficient to control current to trailer battery.

Any camper dealer can help you with this setup.

Thanks for the tips so far. Elden's advise most closely resembles what I was thinking needed to be done. I don't necessarily want to slow charge the battery. There is either a #12 or #14 wire inplace that I want to use. In order to use the existing wire I must limit the current going through it to prevent melting it. Winching a heavy load onto the trailer could draw the winch battery down to 9 volts (??). If the battery is low it will draw much more current than a battery that is near full charge.
BTW Your right about the Camper dealer. RVs are where I got the idea. I just have to find someone who will let me take there camper's wiring apart to see how it works.

[Elden DuRand]

Originally Posted by Phillip Hutchinson

As far as fitting globes in the charging cicuit this will limit the current flow but also it will restict the voltage at the winch battery therefore I believe it wont' fully charge,this has the same effect as using to smaller cable.
Happy cranking Phillip

Phillip:

In actuality, the lamps ("globes") don't limit the voltage that much because of the low resistance of a cold filament. As the auxillary battery voltage, it's resistance falls and allows the voltage to rise.

This is not good for fast charging batteries but does fine for those that are in standby service because there's plenty of time for the auxillary battery to charge before being used again.

Take care - Elden

[Elden DuRand]

Originally Posted by Phillip Hutchinson

As far as fitting globes in the charging cicuit this will limit the current flow but also it will restict the voltage at the winch battery therefore I believe it wont' fully charge,this has the same effect as using to smaller cable.
Happy cranking Phillip

Phillip:

In actuality, the lamps ("globes") don't limit the voltage that much because of the low resistance of a cold filament. As the auxillary battery voltage rises to that of the main battery, the voltage difference between them becomes less and the lamp cools. Th resistance of the lamp falls and allows the voltage of the second battery to rise to close to that of the primary battery.

This is not good for fast charging batteries but does fine for those that are in standby service because there's plenty of time for the auxillary battery to charge before being used again.

Take care - Elden

[Fred_M]

If you want to go the lamp method use a small 12 volt headlamp from a garden tractor. It will flow about 10 amps max which will charge the battery pretty fast yet keep even 14 gauge wire cool. A car headlight flows even more current, but I would use 10 gauge wire for it.

Isolators, as used in RV's, are easy to wire in and come with detailed instructions. They are basically just big diodes to keep current from flowing backwards from the hot to discharged battery, but allow current flow to the batteries. If you supply a constant voltage to batteries they self regulate the current themselves. Even using an isolator requires 6 to 8 gauge wire to the aux battery with a ~60 amp altenator. So a lamp would be a good idea with 12 gauge wire. It don't take long for an overload to ruin a truck. Bring your weinies. Fred

[Forrest A]

You can buy a two battery charging system that would monitor the level of the battery and would only charge it when it is needed. I think JC Whitney sells them.

[ListerDiesel]

Generally speaking, the impedance (resistance) of the wiring will usually limit inrush and charging current into a battery unless it is 'seriously' discharged, in which case it is probably beyond redemption anyway.

We have used standard UL 16g cable (or 1.5mm sq in European terms) to link up a trailer battery, always ensuring that a good quality fuse is fitted. The volt drop in the cable and vehicle wiring allows 2-3 volts differential between the vehicle battery and the trailer battery quite comortably, and as the charge current falls away, so the volt drop decreases. It is ALMOST self regulating, but a fuse is a MUST.

Once the battery starts accepting charge, its terminal volts will rise fairly quickly, so the sooner you get it on charge and the vehicle moving, the better it will be.

Putting bulbs in the circuit will certainly limit any current, but will also restrict the ability to charge the battery in the first place, but it's a safety measure than has its advantages if the state of charge of the battery is completely unknown.

If you are concerned about current flow, remember Ohm's Law and work out that 1 amp through 1 ohm drops 1 volt, so if your cable to the battery and the return cable (there has to be two!) come to more than an ohm, then at about 3 amps you're out of volts to do any charging anyway!

Never leave a lead-acid battery of any type standing discharged, always get it straight back on charge or it will sulphate and you will lose battery capacity. Nicads are much better, especially vented/wet types as they will stand for some years in a flat condition and still work afterwards. DON'T do that with your car or trailer battery! Equally, don't overcharge it or you'll lose water and in severe cases lose plate material and capacity.

I probably ought to point out that our company manufactures battery chargers in the UK :-))

Peter