electrical for John T

I have no electric in the barn where I keep my tractors. Some time the batteries get weak after sitting a while. If I wanted to use an inverter from my car just to boost the charge to start. to run a battery charger, how do I know how much power the charger draws and what size inverter would I need????? Thanks Henry

Okay, you mention "boost the charge" that sounds more like a fairly high amperage, say at least 20 up to as much as 50 amps or more charger (depends on size of charger and condition of the weak battery). My big honkin charger has like a 100 amp boost feature. On the other end of the spectrum, a trickle or maintenance charger is only a few amps.

Lets do a few calculations:

If for example a battery chargers output is say 14 volts and its delivering say 20 amps, that's 280 watts. If you go the inverter route to run a 120 VAC input charger, neither the charger or inverter are 100% efficient, so if we use say 80% overall efficiency you could be looking at 125% of 280 watts or the inverter could be consuming 350 watts. A typical off the shelf inverter size is say 400 watts and it looks like that could power a charger that could deliver 20+ amps. BUT CONSIDER the inverter while operating (due to inefficiencies) is going to have to draw MORE THEN 20 AMPS OUT OF THE TRUCK BATTERY and it would eventually discharge unless the engine was running and powering the alternator!!!!

NOTE there are short term boost features and surge ratings and the whole duty cycle thing that can affect all this, these are ONLY approximations. If you want to figure things exactly you need all the specs and ratings and then do the math.

Now just do the math again, so if you needed a charger that could deliver 40 amps at 14 volts that's 560 watts and at 80% overall efficiency the Inverter would need to be around 1.25 x 560 or 700 watts.

It would be more efficient to just use a set of jumper cables and go direct to boost charge the tractor battery as that's more efficient then the losses using BOTH a charger PLUS an Inverter. However using a good 120 VAC powered charger can allow a more controlled and regulated slower charge then a set of jumper cables so that's an advantage.

NOTE the inverter is drawing power you know so you may want to leave the truck running as the battery is charging so you don't run the truck battery down BUT IF THATS SO MAYBE JUST USE JUMPER CABLES ?????????

Other options, a small solar powered system at the barn would only have to have enough power to operate maybe a small trickle/maintenance charger such as 2 amps and that's only like 28 watts!!! powered

Theres more but that's enough for now, I'm sure others will offer other good options.

DISCLAIMER the above are typical ball park figures, I did NOT take time to research inverter and charger sizes and efficiencies and types and all the specs and ratings, so don't anyone have a calf if these figures aren't perfect NO WARRANTY

John T

How far is the storage area from actual power? If not too far, investing in a heavy gauge extension cord might work (10 - 12 ga.). HTH

A couple thoughts:

1 - As John T points out it would be simpler, faster and MUCH cheaper to simply jump the tractor from the car rather than try to charge the battery via inverter and battery charger.

2 - You might consider a solar battery tender such as at the link below. It'll maintain the battery at full charge indefinitely for less than the cost of decent extension cord. A maintainer will help the battery last longer too!
solar battery tender

How about a solar charger on the barn roof?

There are a lot of 110V generators from $100 to around $250 that have a 12 volt 8 amp plug on them and will run for 8 to 10 hours on a gallon of gas.

Just jumper it. I have a set I made of welding cables 20 feet long that will reach the front of a car by parking behind it.

One key point has been left out of this discussion. Modified wave inverters have a hard time running conventional battery chargers. A 10 amp battery charger will barely make 3-4 amps when hooked to a common modified wave inverter. A full wave inverter works well. So does a high tech electronic battery charger which I doubt you have. Common battery chargers need 170 volts to work when plugged into a 120 VAC outlet. Cheap inverters only make 150 volts at the peaks and valleys of the Hertz cycles.

I use a Duracel Powerpack 600 with jumper cables for remote jump starting. Charges from a 12 powerport. Works very well - even on diesel tractors.