Battery gadget to stop it running flat

[Jonny Boaterboy]

Hey there, My lovely wife has brought me a fridge that runs off the cigy socket. It does not have a built in cut out so if the battery runs low it just keeps on going until it is flat. I want to put in a 3 socket cigy lighter point to supply a constant live from the battery. Does any one know of a electrical device that can be wired in that will turn the sockets off or cut the power if the battery starts to get too low?

Thanks

Jonny

[crazymac]

A battery monitoring thing from a split charge system should do. Try TMax or Maplins

[Mud_Medic]

Hi Jonny

Fridges eat power. Which type do you have? If it is a Peltier effect type, they usually pull about 4 amps, if it is an absorbion type (which can be powered by mains/gas/12v) then they usually pull about 8amps. They will quickly flatten any starter battery.  (But I guess you worked that out, because you are asking the question!)

The only safe way to do this is to have a second battery (ideally deep discharge type) and power the fridge from this. You then use a split charge system (Relay - simple and reliable but needs a connection to the alternator or Voltage sensitive relay which does not). That way, what ever happens, you don't discharge the main starter battery, and can always start the vehicle.

If you really want a cut off device, how about something like this http://eco-energy.ca/product/page1/page1.html

The problem with these devices is, there is not much power left in the battery to start a vehicle. If it starts first time, you will usually get away with it, but.......


Ed

[crazymac]

X Eng do this split charge system http://www.x-eng.co.uk/X-Charge.asp but if you want the batteries they sell (Numax) then go to http://www.tayna.co.uk/Numax-CXV-X-1000-Amp-P7632.html as they are cheaper!

Also Vehicle wireing products do a split charge system http://www.vehicle-wiring-products.eu/VWP-onlinestore/accessories/towing.php#scr

[Jonny Boaterboy]

Thanks Ed and crazymac, Just what I needed, just to run a few more points by you, First off, 2 batterys and a split charging system would be the ideal way to go..... but funds don't permit! so I have one blue top Optima battary (marrine grade deep cycle battery) fitted which will have to do all the work!

The fridge is a Waeco, as to what type I'm not sure, It has a fan to draw air over a metal fin type element which cools the inside down, which it does very well, tried it the other day and it got the tempiture down to -5. Here's the spec:

Power input: 3A/36W
Cooling capacity: Max 25 deegre C  below Ambient temp.
Cooling Unit: thermoelectric elements, cooling only

I go away camping in the middle of nowhere for up to 4 days at a time, so here's the plan: Take a feed direct from the battery and run the cable to a 3 socket cigy lighter point in the boot (do you know what type of cable to use for this?) on the positive wire fit a device that will cut the power when it starts to get low (the eco-energy switch looks like it will do the job?) so I will still be able to start the Range Rover. The eco-energy swich says you can select diffrent voltages that it will switch the power off.... how low can you go before the battery will start to struggle to start the engine?

Thanks for all your help... mudclub is great!

Jonny

[Mud_Medic]

Hi Jonny

If the fridge draws 3 amps, then that is not so bad. But, Optima batteries don't have a large reserve capacity at either 50 or 55AH.

The life of the battery will depend on how deep you discharge it. If you go down to 50%, the life is not reduced to much, but if you discharge down below 70%, the life of the battery is seriously reduced. (shame you bought the Optima, you could have purchased a deep discharge battery, split charge relay, wire and starter battery for a similar amount. But what is done, is done!)

As for wire.. the thicker the better. 4mm cable would be good, but 2.0mm or 2.5 would probably do OK. (I know the fridge only pulls 3 amp, but I would still avoid 1mm as there is going to be a long run from the engine compartment)

A little tip which costs nothing... If the fridge has a temperature dial.

When you set out in the morning, set the temp as low as it will go. That way the fridge will be on all the time and get really cold while there is engine power. When you stop for the night, turn it back to the normal temp, and that way you will get a couple of "free" hours without the fridge drawing power!

As for what voltage to set the cut off device to... I can only guess. The lower the voltage, the longer run you will get (and less likely for the milk to go sour), but the more likely you are to get stranded.

If I was you, I would buy a jump start pack as an insurance policy, because if you can't start the vehicle, you are in serious do do.

Ed

[Jonny Boaterboy]

Thanks ed, as for the optima, it was a gift from my dad so I did not chose it but received it gratefully  :dance: out of interest which battery make would you recommend?

The fridge does not have a temp gauge its on or off! but kind of planing to run for a few hours at a time, it comes with a mains adaptor so I can pre-chill it before  leaving, chill on the way, and then turn off overnight. and see how we go from there....... My wife has kind of come round to the idea of me getting a second battery so a split charging system may be on the way! hence the interest in battery make!

thanks for all your help

Jonny

[marky]

I think i'd park up facing downhill, just incase! :lol: