Connecting the winch to the Battery

[Aussie Frontier]

I already have my winch mount for the hitch and pick up my new winch tomorrow .
My question is thus
I have the option on increasing my battery size already wired in the tub (runs my work lights and compressor etc )and then running leads ( 25mm2 welding lead) to the front and rear of the truck with 350Amp Anderson plugs.
Battery in the back is only a small bike battery but connected via 40amp fuses to a Battery Isolator so all done correctly with 4GA cable rated at 110amps


Or just connect the same leads to my stock battery.
If I connect to the stock battery how have others connected to the factory battery connector? From memory its got the fuseable links etc .

Reason for running leads to both ends of the truck is I can jump start from either end and when I eventually do a front hitch I will be able to use the winch front or rear.
I am leaning towards connecting to the stock battery simply because I wont have to make a new battery box and buy a bigger battery for the tub.

 

[Old.Tony]

I connected mine to the battery post side of the connector, so there was nothing between the cable and the battery terminal.

The problem with doing that and running the big heavy cables to the rear is that they will carry a lot of current and if you snag something that shorts that cable to the chassis then it's all over red rover.

You'd need to put a 500A fuse in to protect that. I know Supercheap don't sell them that big and I doubt Jaycar do either. Maybe Farnells?

 

[Aussie Frontier]

I could run the cables down through the chassis rails in conduit possibly. Will have to look at that. In theory we should be able to run fuses in parallel to get the higher rating.
The cables currently run tied the the factory harness along the drivers side into the tub.
Being an asphalt queen am hoping it never gets in a place to snag anything lol

 

[dunkmuddie]

i used heavy duty circuit breakers from jaycar that way no need to carry spare fuses not sure on amp rating but never had a problem. off my start battery cause it can handle higher current draw

 

[Aussie Frontier]

Have been looking and best I can find is 250amp circuit breakers mmmm maybe 2 in parrallel lol

 

[simonk8]

Remember that the fuses sole purpose is to protect the cable. In your 1st example of connecting the exsitng 25mm2 cables to the main battery, the maximum current carrying capacity of the cable would be (with no de-ratings applied) would be about 90A with a maximum temp of 75 degrees. Ofcourse you can run your cables hotter, but the insulation will degrade over time. So, putting a 250A (or two in parrallel) fuse on this cable is a waste of time, the cable will melt before the fuse blows. For a 500A supply (the winch won't pull 500A constantly, the current should drop as the vehicle begins to move) you would need about 400mm2 cable, pretty hard to install in a car. Lets say the average current for a winching operation was 250A, you would need around 120mm2 cable. Haven't even considered the volt drop yet!

In my opinion, to install a properly sized and protected system for a winch in a car is too costly and the cables are too large to find a place to put them and you cant terminate a 400mm2 cable to the terminals of a winch! I went through all the scenarios at the time of installing my winch, and decided (trading off risk vs cost) that the best way is to install the cables that come with the winch (probably 25 or 35 mm2) wired through an isolator located at the battery. Most times the isolator will be off thus if the cable shorts, no problem. When winching with the isolator on, I just monitor the cable temp by touch (your case might be different in that my winch is only at the front), if there is a short, you will tell pretty quickly, then just turn the isolator off.

To further reduce your risk, like you say, run the cable in conduit and in the chassis rail. Also, in your case, you can't really run your winch from the second battery with the 40A fuses, as I suspect you want the second battery to be connected to the main battery all the time, thus the no fuse / isolator setup described above is no good.

If I was you, I would just run a new set of cables just for your winch. Considering the volt drop (rough calc) on 25mm2 flexible at 75 degrees with a load of 250A and a route length of 5m say, it would be about 2.3V. At 12V this is about 20%. this is far too high. To get around 5% max volt drop (0.6V) you would need to run about 120mm2. This is big cable for a car. In this case,The max length you can run in 25mm2 is about 1m.

Remember also that as the voltage drops, the current increases as the motor is still trying to draw the same power and as the current increases, the resistance of the cable increases, which makes heat exponentially I^2R which is a circular effect untill your cables catch fire!

To summarise, the minimum cable size to do the no fuse isolator setup would be 120mm^2. You will need to consider the cost of this vs the need to have a winch at the back. Unless you know an electrician, for a bloke off the street for 120mm^2 flex you will need a second mortgage, not to mention how difficult it will be to install in a car.

 

[Old.Tony]

Simon, based on that I'd be recommending a second cranker that can be stored in the back and smart-charged between uses. 120mm2 cable? That's what, about 12 and a bit mm across the conductor, that's not too bad. It's a bit heavier than standard weld flex. The 400mm2 is about 22.5mm across the conductor. That's heavy cable. What would 12m of that weigh?

 

[Aussie Frontier]

Ok a little confused here
The second battery in the back would be doing all the hard work from my understanding and the 40 amp fuse is only to stop the charge going higher than the cable is rated.
Evereything I can find from guys using a similar winching setup from the US is they pretty much rely on the winch not overloading a lower rated cable.
From what I can figure a 25mm2 cable should easily handle 200amps with short bursts to higher amounts .
The winch cables supplied are not that big so even the manufacturer is under specing the cables .

Oh yeah and multistrand welding flex in theory should handle higher currents without issues rather than using for instance high current stereo cables

 

[Old.Tony]

I think we were under the impression that one of your options was a small aux battery in the back that didn't supply power to the winch, and you could run large enough cables from the front so that you could power the winch at the rear of the car. That's where the discussion landed - carrying that much low-voltage current over that distance is problematic.

I still can't get over the thought of a 22mm-thick conductor in a car.

 

[Aussie Frontier]

Actually I can go a little better lol
I went out to GasWeld welding supplies this afternoon and can get 35mm^2 or 50mm^2 cable so 25mm = 250 Amp, 35mm= 350 Amp and 50mm = 500Amp.
Weight gets to be an issue then lol.
Am thinking maybe 35mm^2 cable from the main battery with a 400Amp circuit breaker and 350Amp Anderson plugs will cover the bases.

However
When I was talking to one of the engineers at work he brought up a damm good point. I will be relying on a single pin in the hitch to hold 12000lb
He actually suggested that running the 250 Amp cable with 300 Amp circuit breaker might be a much safer outcome.
If I run it so it will in fact run the full 12,000lb it could actually be electrically ok but structurally dangerous as basically the hitch isnt rated for that much weight.
Running it as a 9000lb setup may in fact be a safer alternative all ways round.
9000lb would run approx 250Amps so limiting the setup to that could be the best way out

 

[Krankin]

Am thinking maybe 35mm^2 cable from the main battery /QUOTE]



this will be fine.... go to 50mm welding flex if the winch to batt are at opposite ends of the vehicle.

Remember....welding flex is different and has a better current carrying capacity..size for size, to auto flex cable

 

[Old.Tony]

However
When I was talking to one of the engineers at work he brought up a damm good point. I will be relying on a single pin in the hitch to hold 12000lb
He actually suggested that running the 250 Amp cable with 300 Amp circuit breaker might be a much safer outcome.
If I run it so it will in fact run the full 12,000lb it could actually be electrically ok but structurally dangerous as basically the hitch isnt rated for that much weight.
Running it as a 9000lb setup may in fact be a safer alternative all ways round.
9000lb would run approx 250Amps so limiting the setup to that could be the best way out

I think your engineer forgot two vitally important points:

1) Your car isn't 5,300kg. Your car weighs less than half of this - and also weighs less than what the pin is rated for.

2) You're not hanging your car vertically off the pin, you're pulling horizontally, so you aren't even pulling the full weight of the car.

 

[Aussie Frontier]

Damm good points there Tony
Am seeing am only planning on dragging race cars out of sand traps they in reality would only be like a 2000kg load at best.
35mm should do the trick as it will easy hold 400amps for a short period. If I went with the 500Amp cable I would be overkilling it I think by about 100 amps
Running in the 500 cable would mean I would have to wind up the suspension on that side to compensate lol

 

[joshman]

He actually suggested that running the 250 Amp cable with 300 Amp circuit breaker might be a much safer outcome.

No offense, but this guy is an idiot. Your protection needs to be rated LOWER than what your cable can safely carry. Otherwise you give the potential for damage to the cable (and the rest) before the protection cuts in. 50A is a huge current, I daresay enough to weld a few things together.

Seriously, when choosing cable size use this formula:
Current you need < circuit breaker size < cable's current carry ability.

As an example, If you require 250A, you have a circuit breaker that will protect at 300A and a cable that is rated to carry 350A.

Last thing you need is an electrical incident.

 

[mitch92]

Exactly what joshman said x 2

ALWAYS have the protection device (Fuse/breaker) a LOWER rating the the cable it is protecting. It is there to protect the cable, not the device at the end of it.

 

[justdrinkbeer]

I wired my dual battery in 50mm welding flex, only because I happened to have some spare. Was a bit of a pain to get to the tub because I went through the cab but not too bad.
It doesn't weigh that much

 

[Aussie Frontier]

Josh
he wasnt talking about cable protection.He was talking about not overloading the hitch mounting point . Not electrical protection but mechanical.
I realise you use circuit protection to protect your cables not the load. The cable will easy handle 300 amps short term but I didnt want it going above that.300 Amps would limit the load to approx 3tonne .If the breaker goes it means I am trying to pull too heavy of a load .
That is the reasoning he was using.

I wired my dual battery in 50mm welding flex, only because I happened to have some spare. Was a bit of a pain to get to the tub because I went through the cab but not too bad.
It doesn't weigh that much

Did you run a second earth or just bolt direct to the chassis

 

[justdrinkbeer]

Bolt to chassis below the tub & ran a second earth to main battery. Didn't really need to as compressor is the highest load accessory but did it anyway.
Fused both ends @80Amps I think, no intention to use for cranking/winching etc