Can I recharge my portable battery from vehicle 12v port while running engine?

[DaveM]

Planning last minute trip for next weekend with wife and kids to east side of Lassen National Forest. Taking my Dometic CFX 35 fridge. I usually run the fridge off a basic West Marine 75 amp hour deep cycle batt that seems to give me at least three solid days of power in normal conditions. I'm planning on 4 or 5 days this trip and I'm not sure batt will last in hot weather. When driving I usually plug the fridge into a 12v outlet in the bed of my truck to save the batt.

If my batt discharges below the fridge cutoff level, can I recharge it a little by plugging the batt into the truck beds 12v outlet and running the truck for a while? Will male to male 12v plug work for that? Would I get anything like a decent recharge in just 15 - 30 minutes of running the truck if I really needed it?

David

 

[vartz04]

Probably not in 15-30 mins. You'd be best suited with a 100 Amp solar panel and a charge controller. You can get the HF stuff for less than $150 and then it's charging whenever the sun is out.

It would likely take 12+ hours of the truck running to get it from 11 volts back to 13-14 volts

 

[DaveM]

That's what I was guessing. Portable solar panel to extend battery is best, but not sure I can find what I need locally before we go as I have no idea about required specs (and no money for high end systems). I wouldn't need anything that kept up with fridge, just enough to extend the batt discharge time from 3-4 days to 5-6 days.

 

[ducktapeguy]

Not an expert but I've done something like this before. It will work under certain circumstances.

1. As long as your deep cycle isn't drained too far down it'll work. If you draw it down too low the initial current will likely blow your outlet fuse
2. There might be too much resistance in your factory outlet wiring to charge the battery effectively
3. At idle the alternator probably isn't putting out much output so you might need to increase it to 1500 to 2000 rpm to get it to charge faster

If the deep cycle isn't mounted, might be better to just hook up a set of jumper cables directly from the battery and run the truck at high idle for a bit to top it off every day. Won't fully charge it but will at least get some amps back into the battery.

 

[camperthingy]

Sounds like your West Marine battery is a stand alone. I would take jumper cables and connect to the (truck battery) to the West Marine battery and start truck. You will charge the battery faster because of the larger wire in the jumper cables. If you use the male 12 volt plug it will blow a fuse either in the male plug or the truck fuse block. That is what I would do.

 

[DaveM]

Good advice. Thanks.

Wondering about units like this for keeping batt topped off and extending service? Is 22watts too low to make a difference? The HF stuff is closer to $200 locally, more than I can pay rifght now.
http://www.homedepot.com/p/Nature-P...ontroller-for-12-Volt-Systems-42022/300854090

 

[vartz04]

Look online for coupons for the HF one. I just saw one last week where it was $129 or $139. The 22 watt will help but not much. It puts under 2 amps in perfect conditions. Most of the time you'll get less than 1 amp with changing sun angles and clouds. That's not going to do much

 

[john61ct]

If money is that tight, time so short, don't spend on suboptimal stuff for just one trip.

Wire up a good connection straight to your battery or alternator with decent gauge wire.

Ideally to an Anderson plug well located inside your vehicle, then an adapter cable goes from there to ends suitable for your battery posts, worst case jumper clamps.

Whenever you start your vehicle, plug it in to charge. Days you don't go anywhere, run the engine for a while at high idle, an hour a day should be more than enough.

Unplug before you shut the engine down.

Do some more research about a good solar setup when you get back, just make sure you place your orders long before the next trip.

 

[john61ct]

Don't use ciggie ports for high amps like this, they often fry well before their rated 8-10 amps.

 

[DaveM]

I have a Blue Sea fuse box behind rear bench wired with either 6 or 10 gauge direct to starter on 30 amp fuse, need to check. Have miscellaneous heavy marine plugs at same gauge at home, just need wire to connect it all and a couple of rings ends. I think that will work. We'll probably take a short day trip or two as well so that's a good time to plug in the portable unit and charge it while driving around. Thanks for helping me think this out guys.

 

[DaveM]

Well, I'm back. I made a simple fused connector from blue sea fuse box to portable batt for charging while driving. I had one day with about 2-3 hours worth of driving with batt hooked up and charging. No direct testing of batt voltage but I was able to get some extra time out of the charge based on past experience. Will need to do a real test at some point but seems to work.

 

[calicamper]

Good advice. Thanks.

Wondering about units like this for keeping batt topped off and extending service? Is 22watts too low to make a difference? The HF stuff is closer to $200 locally, more than I can pay rifght now.
http://www.homedepot.com/p/Nature-P...ontroller-for-12-Volt-Systems-42022/300854090

I have two 10watt panels that keep my setup charged. But my burn rate is about max 8 amps in a 24hr solar cycle. 22watts of solar in CA will do about 1.5amps per hour generation. But your fridge is burning around 2-2.5 amps an hour. So youll still be loosing juice. If your short on resources for a solar set up you could double up on the 22watt that will cover your fridge barely and might give the controller an amp or slight more to dump
Into the battery. But That only gives you say 4-6ish amps banked for overnight so your still taking a loss.

Minimum guess you need 80watts to cover fridge and minor other power needs to keep the battery topped up.