Using existing wiring

[ThomD]

Sometimes I get the craziest ideas. My Suby has two unswitched cigarette lighter ports. If I plug my Engel into one and a 30W solar panel into the other, does that mean I'll have the fridge pulling power and the panel adding power?

 

[DaveInDenver]

Sometimes I get the craziest ideas. My Suby has two unswitched cigarette lighter ports. If I plug my Engel into one and a 30W solar panel into the other, does that mean I'll have the fridge pulling power and the panel adding power?

Yup, the system is the sum of all the sources and all the loads. This is not crazy at all.

 

[ThomD]

but, there's always a but, unless Subaru has changed their ways or unless you've modified them yourself, the 2 power outlets are only active when the key is turned on.

In other words, once you shut down your engine, neither the solar panel nor the fridge will be hooked up.

Thanks for the reminder John. It turns out there is a trivially easy mod to make them unswitched.

 

[ThomD]

John,

I'm with you on the concerns. If the 30W panel put out exactly 2.5A all the time (which it won't), I'd be net flat for power use. The key piece would certainly be having 1. a better than stock battery and 2. a battery saver

http://koolatrononline.stores.yahoo.net/koolatron-12v-battery-saver.html

Now I just need somebody to vouch for the battery saver.

The final bit is that this setup would only be used for up to 6 hours at a time.

 

[DaveInDenver]

Depending on what sort of fridge you run, you'll probably be drawing more amps than a small solar panel will replace. A 30 watt panel will only put out about 2.5 amps at 12-14 volts at it's peak.

See back issue of Overland Journal or search here, typical Engel, Waeco and similar overland fridges run a couple of amps draw with roughly 2x in rush. A 30W solar panel should add a comfortable margin to cover a fridge. Say an Engel MT45 runs 2A at 50% duty cycle for 24 hours, that's about 288 W-hr (2A x 0.5 duty cycle x 24 hours x 12V) of load. A 30W solar panel at 75% efficiency plugged in over a good 10 hour day will add 225 W-hr of capacity (30W x 0.75 x 10 hours), which is a significant reduction in draw down on the battery. Obviously it all depends on how much sun you get, the intensity of the sun, how efficiently the solar panel charges the battery, etc. Also if you turn the fridge down at night to reduce cycling, that helps tremendously. But it doesn't take a ton of solar panel capacity to offset the fridge.