I pull a backhoe on a trailer behind a 1-ton GMC truck. Sometimes when it
is cold I need to "jump off" the backhoe from the truck's two batteries
while it is loaded on the trailer. Since the jumper cables are too short to
reach the tractor from the front of the truck, I would like to run two
permanent cables to the back bumper of the truck . Then I could hook
regular jumper cables from the tractor to the terminals on the back bumper.
Question is: What type and size cable should I run? Would 4/0 copper
"entrance" cable do? This is stiffer than welding leads, therefore, harder
to work with. But if it gives me more cranking amps it would be worth the
trouble. Does a 4/0 copper with a few thick strands carry more CRANKING
amps then a 4/0 with many finer strands? Is welding lead the best wire
jumper cables? What size? Thanks, Chief
At DC, I don't think there is a measureable difference between the two cable
types. They make heavy guage cables with large plugs on them for winch
applications. This is so you can use one winch on your vehicle by moving it
from the front to the back. I would look at that type of cable and then add
a compatible plug to the end of a set of jumper cables.
Charles Perry P.E.
I know that back hoes can be a bit hard to start on cold mornings. I
challenge you that 4/0 is needed. I would think that #4 maybe less sized
conductors would be all that you would need.
Your might consider a inverter and a battery warmer. Smaller wire for sure.
You would need less than 1500 watts.
The biggest concern would be the routing and protection of the cable from
the front to the back of your truck.
AWG is a standard that relates to current carrying capacity of the wire.
All current values are for continous draw.
The calculator at the bottom can be used to determine the voltage at the
backhoe batteries (the box labeled "voltage at load end of circuit").
Welding wire is usually the cheapest solution.
Here's how I'd go about solving this...
First, make sure the charging system on the backhoe is in good order.
It may not be keeping the battery fully charged. Make sure the top
and case of the battery is clean. You might also see if there is a
key-off drain on the backhoe battery. If there is, find it and fix it,
or install a battery cutoff switch in the negative cable of the backhoe
battery. After you drive the backhoe up onto the trailer and shut it
down, flip the cutoff switch and your battery is guaranteed to be
disconnected from everything on the backhoe so it won't discharge.
Just remember to flip the switch again before you fire it up.
Second, if the backhoe battery is fully charged and it's still hard to
start (old engine, it's cold out, etc), you might try warming up the
battery, as has been suggested. You can test this theory with a plain
old drop light / trouble light. Some morning when you don't have to
go anywhere, put the light near the battery (under is best) on the
backhoe and leave it plugged in for an hour or so. Then try starting
the backhoe. If it starts up, you can either warm up the battery
before you leave the house, or install a heater on the backhoe.
There are battery heaters available that work off of 120 V, but then
you need an inverter to get the 120 V. If you have a long enough drive
from the house to the job, or can go out and plug in a connector some
time before you leave, you might install a 12 V heater on the backhoe.
Buy a couple of double-contact automotive bulb sockets and mount them
under the battery on the backhoe such that the shells are grounded to
the frame. Put an 1157 (35 W) or 2357 (37 W) bulb in each socket. Wire
all four wires together and to a piece of 14 gauge or better wire.
Also connect a piece of 14 gauge or better wire to the backhoe frame.
Run these wires to a 2-wire connector on some handy place on the
outside of the backhoe. Run two more 14 gauge wires from the trailer
connector to the mating 2-wire connector. At the trailer connector,
connect the hot wire to a separate contact - don't hook it to the
running lights as the new bulbs probably draw too much for the running
light circuit. Hooking the ground wire to the existing ground wire
in the trailer connector is probably OK, as long as you upgrade the
ground wire on the truck side of the connector to at least 14 gauge
as well. On the truck side, run a 14 gauge hot wire from the new
contact to the battery, and put in a 15 A fuse at the battery. Now,
whenever the trailer connector and the 2-wire connector are both
plugged in, the backhoe battery is getting heated. You probably
don't want to leave this plugged in overnight as it would drain the
truck battery too much. But plugging it in an hour or two before
you leave should be fine.
Third, running permanent cables is also a valid option. Tow trucks
often have cables that come in two parts. There is a short part
(three or four feet long) with lugs on the ends of the cables for
attaching to the battery. The other end has a two-pole "Anderson"
high-current DC connector, which gets mounted to the truck grille.
The long part of the cable (ten feet or more) has jumper clamps on
one end and the mating Anderson connector on the other end. The only
problem with this scheme is that the short end of the cable is probably
too short to reach the back of your truck.
Welding cable is probably a better choice than entrance cable, since
it's more flexible and therefore better able to withstand the vibration
of an automotive application.
What I'd do is to buy a chunk of #2 or #4 welding cable a little bit
longer than the truck, some copper lugs to suit that cable, an
Anderson connector and the terminals for it, a length of split
corrugated tubing as long as the welding cable, a set of jumper
cables long enough to go from the bumper of the truck to the backhoe,
and some miscellaneous zip ties, mounting screws, etc.
First, cut the clamps off of one end of the jumper cables, and put the
Anderson connector terminals on the cables. You can solder them on (use
rosin-core solder and a propane torch; they're too big for a soldering
iron) or crimp them on - trade beer (or whatever) for use of the crimp
tool with an electrician friend, or possibly rent one.
Next, figure out where on the bumper you're going to mount the other
Anderson connector, and cut a piece of welding cable long enough to go
from there to one of the frame rails on the truck. Put the Anderson
terminal on one end and a lug on the other end. Put the corrugated
tubing over the cable. Use an existing hole in the frame or drill a
new one. Use sandpaper to get the area around the hole down to bare
metal, then bolt the lug to the frame. Use a lock washer or Nylock
nut on the other side - don't use a sheet metal screw or lag screw.
Spray-paint the completed connection to cover up any remaining bare
metal. Plug the terminal into the Anderson connector and bolt the
Anderson connector to the bumper. Use the zip ties to dress the wire
up out of the way.
Up front, locate another hole in the frame rail near the battery, and
prepare it the same way (bare metal). Install a cable from here to
the negative terminal of the battery - you can either make one out
of lugs and welding cable, or buy a ready-made "switch to starter"
cable at the auto parts store. (Yes, the battery is grounded to the
frame already, but this is typically through a #10 or so wire that
will melt if you try to jump the backhoe with it.) Use more corrugated
tubing over this cable.
In the back, attach the Anderson terminal to the long piece of welding
cable. Put the corrugated tubing over the cable. Plug the terminal
into the connector, and then route the tubing+cable to the front of
the truck. Avoid moving parts and anything that gets hot. Get the
thing secured to the frame or body at least every 12 inches. At the
front, crimp a lug on the cable and attach it to the positive terminal
of the battery.
You may want to make a cover for the Anderson connector on the bumper
so it doesn't get mud and water in it. You might be able to find a
vinyl tube cap that will stretch over the end. Or, instead of bolting
the connector to the bumper, get a small plastic toolbox and bolt that
to the truck. Cut a slot in the side of the toolbox for the cables.
When you're not using it, put the connector in the toolbox and latch
To use the rig, make sure the jumper clamps aren't touching and then
plug in the Anderson connector on the jumper cables to the one on the
truck bumper. Connect the positive clamp to the backhoe battery and
the negative one to the backhoe frame, and start it. To disconnect,
unhook the negative clamp first, then the positive, then the Anderson
You can probably get all of this except the Anderson connector at your
local electrical supply house. You can get the Anderson connector and
You probably want the 175 amp kind. If you do decide to go with
thicker wire, you can go with the 350 amp ones.
<<I would like to run two permanent cables to the back bumper of
the truck I would like to run two permanent cables to the back bumper
of the truck.>>
Be extremely careful to protect the cables mechanically throughout
their length, and to protect the terminals against accidental
contact. If a piece of metal accidentally shorts out cables that
big, powered from a big battery, the cables can melt and throw molten
metal, and the battery can explode, spraying sulfuric acid in all
Starting-fluid may help. It is available from truck supply
stores, in pressurized spray-cans. Be careful with it, as it is
highly flammable, and the pressure is high inside the cans.
alvarez at alumni dot caltech dot edu
Im from the UK so dont know what a backhoe is. I would suggest checking the
charging system , is battery AMP/HOUR capacity low ,or quite simply charge
the battery from the vehicle system as done in caravan trailers.
AFAIK, we (Brits) call backhoes by the manufacturer's name
- hence, JCBs (like hoovers being, well, Hoovers)...
Back to the OP, I may be being a bit wimpish but I would
certainly protect the welding cable running down the truck
frame with a fusible link or fuse. The type fitted to
electric fork lift trucks are ideal. Do a Google on fork
lift fuse, if you aren't familiar with them.
Incidently, I also fit fuses like those to the battery bank
for household inverters - having seen the after effect when
a floor-full of deep discharge batteries tries to dump their
stored energy into a faulty inverter. Luckily no one was in
the room at the time - they just heard the bang..
Another thing I would fit for safety, if this could be used
for other things besides the backhoe, is a suitably rated
rectifier in the line - trying to jump start a 24v truck can
otherwise be exciting.
Although I really ought to be good and use the right
non-reversable plug and socket, if it were me, I would
probably just fit a pair of insulated screw-down terminal
posts at the back of the truck.. As I would soon lose the
special cable, (or someone would half-inch it..) and it
would be easier to get hold of a replacement set of normal
jump leads. They can also be used to jump start the truck,
from a passing vehicle, after forgetting to switch off the
Would it be cheaper or more practical to mount an extra set of
on your trailer? You could use a lighter set of cables from the truck
them while traveling. A 110 volt charger could charge them overnight
a convenient outlet. Then you could use a regular set of jumpers to start
We have to jump start motors frequently in the summer. We use 2/0
welding cable. I think my cables are 16 footers.
I was stationed at Ft. Greely AK. in the early '70s. There were 20
amp AC outlets by any place on base you were allowed to park overnight.
You were allocated a 20 Amp, 120 volt circuit to power a battery
blanket, dipstick heater, and lower heater hose heater. This was the US
Army cold weather test site and the concept worked fairly well. In the
winter time you had to keep the engine tuned up, and it helped to put
heavier battery cables in the vehicle. Most of the guys used 2 AWG
welding cable because anything heavier was too stiff to bend in the cold
This is the best solution. I did the same thing. Truck, with 7 pin trailer
plug, already has a full time hot feed. Just get a batterybox and deep cycle
battery. Mount on trailer tongue and hook up to hot feed. You will always
have a charged battery on the trailer. That with a can of starting fluid and
I could always start my massy ferg 50C. even at 10 degrees.
Instead of running a circuit for jumping the backhoe. Consider just running
a couple of small wires to keep the batteries warm. I would think you would
need nothing more than 10 guage to do this. A few minutes of chagre time
before cranking should be all it needs to get the batteries up to temp. If
this will not take care of your needs it means the backhoe batteries and/or
charging system is kaput..
O yeah if you decide to do this remember to disconnect it before starting
the backhoe or you will burn up the wires. 10 GUAGE WIRES MAKES LOUSY JUMPER
CABLES.. Actually I think your problem is a bad battery or charging system
on the backhoe.
The first thing to note is that this is *not* caused by a cold
battery. If the battery is a problem, it's not just because it
Bad idea, and *all* discussion of how to do should be ignored,
because 1) they all fix the wrong problem, and 2) every single
solution is risky in ways that are not worth risking.
Running small cables that length is a waste for as a "boost" for
starting. Any such cable should be used to charge the battery,
and should be /disconnected/ before you engage the starter on the
backhoe. Any such cable that is permanently mounted should be
*very* well protected, both electrically and mechanically.
But all that does is put a bandaid over a few symptoms instead
of correcting the problem.
There are two possibilities for the root cause of hard starts. One
is that the battery or the charging system is faulty. Cold, as such,
isn't the problem if you aren't seeing temperatures of -45 to -50F.
Lots of people who live in Fairbanks AK, or other interior Alaska
locations, don't bother with battery heaters and have no problem
with a cold battery (even at temperatures as low as -70F). I don't
think you are out running a backhoe at -50F...
All that happens when its that cold is the battery has *much*
less charge available, and if the engine isn't warmed up and
ready to start, the battery gives up the ghost before the engine
runs. That is actually a _good_ thing, because if the engine
isn't warm enough to start you *don't* want to warm it up by
Hence, check out the battery and charging system first.
Second, if you are talking "cold" in terms of anything above 0F,
get the engine tuned up. An engine should be able to start *well*
below any temperature that you actually want to start it at!
At sub-zero temperatures you need to think about pre-heating the
engine before starting it. And despite what I said above, you
might as well pre-heat the battery too. That is particularly
true if the backhoe often sits unused for any length of time.
In that case it might well be hard to start even when warm, and
takes a little more battery charge to do it.
As to how to pre-heat the engine... you'll have to be inventive
and consider your specific situation. Typically airplanes, as
one example, are pre-heated with a diesel fired Herman-Nelson
heater. Typically cars and trucks are pre-heated with
electrical heaters. You can install a heat pad under the
battery (or better yet install a trickle charger), *and* install
one of a number of different electric heaters available for the
engine. Circulating heaters should be avoided. Block heaters
that screw into a plugged hole in the block are the
best. Ideally that would all be plugged a handy power outlet for
least an hour before the vehicle is started.
However, you could power it with a portable generator too, if
the trailer is not normally parked where electric power is
convenient. Except that you then have to physically be there to
heat it up, while a timer can be used with a regular power
outlet to allow instigating a future heatup at any convenient time.
Another point that I would suggest is *always* starting the
backhoe *before* you travel with it. That means any problem
will be discovered before you are on the work site. It also
probably means your truck is not yet hooked to the trailer? If
so you don't need long jumper cables at all, because you just
nudge the front end up close and jump start it *before*
attaching to the trailer.
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) email@example.com
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.