Hi All!

Have a bit of a curly problem.

Have a large fridge , 12v 55amp , it sits in a land cruiser with a dual battery setup. Get less than 2 hours from fully charged battery without the engine running. This works great for transporting goods on the road. It does not have a mains (240volt here) connection.

this weekend It needs to be parked at a market for a few hours. Engine cannot be running. There is not enough capacity in the batteries. There is AC power available onsite. its critical the fridge works for the duration.

I have a large 12v power supply (60amps)

Have connected the power supply directly into the fridge unit (disconnecting from second battery) . The problem is the control unit is connected to the vehicle wiring loom which I cannot bypass. So I can be supplying 13.8v DC to the fridge but the control unit only sees <12.5volt (From the battery) and it wont start. If I run the truck it sees higher voltage and everything works. batterys are a bit tired in this vehicle but I doubt they could run this thing for long even if they were new.

there is little time before this market , which is why I'm looking at using a power supply in the interim if possible and getting an auto elec. to setup something permanently after this.

would I be best to disconnect the batteries altogether and connect everything to via power supply? this is awkward for many reasons.

is there anyway to connect the power supply into the mix safely with the batteries connected? it can supply 13.8volts - 18volts at up to 60amp. I am very sketch about even attempting this.

is there a better/easier solution that I am missing?

is there anything inherently dangerous in what I am attempting to do? very careful of all the obvious short hazards with cables etc. testing voltage from power supply under load (connected to a charger) before I connect up to car etc.

 

You could try hooking the power supply across your battery after setting it to 13.8V and then it will keep the battery full while running the fridge. Just make sure the power supply is not set higher to overcharge the battery.

 

I'm a little confused by the wording in your post, partly because I'm in the middle of something, but why don't you just run the thing as normal and simply connect a supply/charger to the vehicle? This will supply the power to the fridge and keep the battery topped up, you'll need around 14.5v (normal alternator output voltage) and the ability to supply enough current to the fridge.

One thing is confusing me though, don't trucks use 24v batteries? Or are you in the US, where everything is a "truck"?

 

ok thanks for the replies everyone!

just to answer some questions

its a land cruiser. twin batteries (in paralell). 12v system.

if its safe to connect it , im guessing like a float charger type deal then I think that's what I'm going to do. Just wasnt confident this was ok. I do have a 12v lead acid capable charger with a float setting , I would have used that but its max output is 40 amps.

so to recap , if I have the charger connected to the battery/ies , set to 14.5v output, max current is 60amp (fridge needs 55) , I should be good to go?

 

If the fridge needs 55A and the charger can only do 40A, your still going to run your battery down, BUT as it's a fridge I would assume it's not drawing 55A all the time, so you may be ok. The one thing i'll say is that with that sort of load you'll probably need to consider how it's connected, ensuring the cabling can handle the current, so either connect at the battery or at the fridge.

A charger isn't really ideal though, any so called "smart" stuff might make it think the battery is faulty when it suddenly see's a massive current draw.

 

ok thanks again everyone.

its working. power supply in paralell with batteries.

unfortunately the PSU doesnt appear to be properly regulated (its supposed to be :/) so took some messing about to get an V output thats enough to start the fans, but doesnt jump too high when they shut off.

much appreciated. the proper transformer is on the way.

cheers