Idiot about to delve into world of electricity ... help?

[bigskymck]

Howdy. Fairly new guy here. I've spent the last couple months rehabbing a '71 Alaskan camper for short 2-3 day ski trips this winter. I'm done with all the work except installing two 210 ah 6 volt flooded batteries in series that I will install in the bed of my F350 dually, outside the camper but under its bench seat.
Can I tap into the site's expertise to make sure I don't die by fire or hydrogen explosion?
Only thing I will be powering in camper is a retrofitted Platnium Cat vented catalytic heater, which draws 5 amps for two minutes during ignition, then .5 amps during operation. No lights. No fridge, no water pump.
Before I leave to ski, I will charge the batteries with a NOCO smart charger connected to AC in my garage, recharging when I return. Not using a generator, solar or alternator for charging.
The heater's positive and negative wires run to two posts in a four-pin Pollak plug on the side of the camper, with a 10 amp inline fuse before the plug. The previous owner then connected his battery (or batteries) with 10 awg wire to the male part of the Pollak plug. Plug them in and the heater works.
--- Is this crude setup safe?
--- I assume I need to ground the outside post of one of the batteries to the pickup's frame? If so, is a common battery cable (6-8awg?) acceptable or do I need something thick and specialized?
--- Do I need to install a 50 amp fuse on the outside positive battery post?
--- Are 10 awg wire leads from battery to Pollack plug adequate? I plan to eventually add a marine fuse block, but is Pollak plug acceptable for now since I am powering just one appliance that is fused inline?
--- Do flooded batteries discharge appreciable hydrogen when they are not being charged? In other words, do I need a vented battery box or just make sure outside air flows freely to side of truck bed when it is sitting in driveway charging?
Thanks. My ignorance, obviously, runs deep and I sense the dangers are great. Any thoughts would be appreciated.
Bill

 

[MarkBC]

...two 210 ah 6 volt flooded batteries in series that I will install in the bed of my F350 dually, outside the camper but under its bench seat.......
--- Do flooded batteries discharge appreciable hydrogen when they are not being charged? In other words, do I need a vented battery box or just make sure outside air flows freely to side of truck bed when it is sitting in driveway charging?
...

I'm not really a battery expert, but I am a chemical engineer (retired) so I have some knowledge of gases and "mass transfer".

Hydrogen diffuses -- spread out and disperses through the air -- extremely rapidly compared to any other gas -- much faster/better than propane or even methane ("natural gas"). If your batteries are in the bed of the truck they'll be FINE -- really no danger of build-up of hydrogen, in my opinion. Hydrogen does not -- cannot -- build up to a big explosive pocket if there's any way for it to spread out. And being outside the camper in the bed of the truck sounds very open to me.
And really, the amount of hydrogen that evolves from a flooded battery is never a lot except when a "reconditioning" cycle is being run, at which point you can actually see bubbles (of hydrogen and oxygen) coming up from the plates.

I use flooded 12v batteries in my Hawk and they're even less well-vented than what you propose, and I've used them that way for at least 8 years or so. No explosions. I'm confident that my setup is fine, so I think your proposed setup will even be more fine -- safe.

On the other hand, I'm just a guy on the Internet...

 

[bigskymck]

Thanks, Mark. I didn't fancy trying to vent my yet-to-be
made homemade battery box if I didn't have to.
Hey, everything I've learned about my hobbies, I've learned from "some guy on the Internet." Appreciate it.

 

[MarkBC]

Thanks, Mark. I didn't fancy trying to vent my yet-to-be
made homemade battery box if I didn't have to.
Hey, everything I've learned about my hobbies, I've learned from "some guy on the Internet." Appreciate it.

Now...when you say "battery box": If it's something sealed up tight then there COULD be a build-up of hydrogen inside it. I was just saying that an open battery in a more-or-less aired area is safe.

 

[Vic Harder]

OK, first things first. You are drawing .5A.

You should never discharge your Flooded batteries below 50%, ever. Doing so will really shrink their life expectancy, and also you may risk freezing them. So you really only have 105 AH to work with.

Getting all of those 105AH out of them is very optimistic, as your AH rating drops fast when the batteries are cold. At -4F you are are only getting 60% of the available AH rating. So only 62 AH

Still, divide that by .5A and you still have over 110 hours of power for your heater fan.

Is that good enough for what you plan on doing?

Good info on batteries here - LINK

Specific Gravity and State of charge info - LINK

Specific gravity and freezing - LINK

Temperature and AH capacity - LINK

 

[MarkBC]

OK, first things first. At .5A 8 12v = 6watts, that heater can run for 17 hours before you need to recharge. That's figured out by taking the AH rating of your batteries and dividing by two. ...

Vic, could you explain this a little? If you took 210 amp-hours total, divided by 2 = 105 amp-hrs (to keep above 50% discharge).
Divide 105 amp-hrs by 0.5 amps...why isn't that 210 hours of run time?

It looks like you took 105 watt-hours, divided by 6 watts, and got 17 hours. But the battery's capacity is given in amp-hrs, not watt-hours.

 

[bigskymck]

Hi, Vic. Good points. I tried to figure my usage as I considered how to power heater. In reality, my ski trips will probably be limited to two nights, simply because the camper's small propane box only holds a 10 gallon tank.
I propose running the heater for one or two hours a night, then burrowing deep into sleeping bag and down comforter (I don't plan on lifting the camper top on most trips, so there is only a small space to heat. Then will fire cat heater up for 15 minutes in the morning to get dressed.
Of course, I'm a native Montanan so I always overestimate my ability to handle the cold. ...
Mark, I wasn't going to put a top on the plastic box I'm planning to put the batteries in. Just seemed odd to angle iron two batteries down to a rubber mat covered pickup bed. So, If I do add a topless box I should just go ahead and add a top and construct a vent tube to the outside? ( Like many Alaskan owners, I use kids' pool noodles to seal the gap between camper top and top of pickup bed, mostly to keep rain or snow out when driving.) I could add a cheap vent exit there.
Thanks, guys. Things to think ab.

 

[MarkBC]

...Mark, I wasn't going to put a top on the plastic box I'm planning to put the batteries in. Just seemed odd to angle iron two batteries down to a rubber mat covered pickup bed. So, If I do add a topless box I should just go ahead and add a top and construct a vent tube to the outside? ( Like many Alaskan owners, I use kids' pool noodles to seal the gap between camper top and top of pickup bed, mostly to keep rain or snow out when driving.) I could add a cheap vent exit there.
Thanks, guys. Things to think ab.

I think a topless box would be ideal.
Maybe put screen over the top to keep squirrels and other critters from putting their tongues on the posts for a thrill...

 

[Wandering Sagebrush]

I think a topless box would be ideal.
Maybe put screen over the top to keep squirrels and other critters from putting their tongues on the posts for a thrill...

Make that a plastic screen...

 

[bigskymck]

Vic: Thanks for the excellent links. I need to bone up and really understand what I'm doing and what I can expect with these batteries, especially in the cold as you pointed out. If I figure out the wiring issues, I'll charge them, take readings and then head up for a night at Copper Mountain and then hope to draw some beginner lessons when I get back and check battery and propane depletion.

 

[Vic Harder]

Vic, could you explain this a little? If you took 210 amp-hours total, divided by 2 = 105 amp-hrs (to keep above 50% discharge).
Divide 105 amp-hrs by 0.5 amps...why isn't that 210 hours of run time?

It looks like you took 105 watt-hours, divided by 6 watts, and got 17 hours. But the battery's capacity is given in amp-hrs, not watt-hours.

DOH... Let me go back and fix that

 

[ntsqd]

If the Pollack plug arrangement works for you I'd leave it. Assuming in good condition there is nothing unsafe or hokey about it. Alternately trolling motor plugs & receptacles are popular for these low-medium current connections. So are the Anderson SB series connectors, though I've never seen a bulkhead version of these.

Batteries in the bed during cold weather may not be the best plan. Re: battery heaters under starting batteries in really cold climes. The reaction in the battery slows down in cold temperatures.

Don't need a truck ground unless you want one. The system can operate in isolation so long as the circuit is complete within the camper (i.e. camper doesn't use a truck ground separate from the Pollack receptacle).

Fuse or breaker at the battery should be slightly greater than the total possible draw from the camper, or the max charging current - which ever is greater. In your application I doubt that is as high as 50 amps.

I use this chart to figure out what wire gauge to use on various circuits: http://www.ancorproducts.com/en/resources/three-percent-voltage-drop

 

[bigskymck]

Thanks NTSQ. Your answers were most helpful. I think I'll use a 30 amp fuse on the batteries and not ground them since the circuit is just within the camper. Keeping the batteries warm is problematic. No room in the camper for them, or I might have gone the AGM route. I am considering using a Stanley tool box others have used successfully as a dual battery box, then constructing proper vents to the outside. I doubt it would help, but I could put some insulation either in or around the box. I assume when it sits on the charger at home, that generates sufficient heat to prevent freezing (although I understand that is a far-fetched scenario if electrolyte is at proper level and they are charged). I guess the real problem is the diminished capacity of the batteries when I'm parked at 9,000 feet and using them.

 

[MarkBC]

...I guess the real problem is the diminished capacity of the batteries when I'm parked at 9,000 feet and using them.

If the only drain on your batteries is the little 0.5 amp draw from your heater, you'l be fine -- for a few days, anyway --- even when the cold diminishes the battery capacity.

Go for it! Just do it!

 

[bigskymck]

You''re right, Mark. I'm overthinking this. I'm going to angle iron these two batteries down to a rubber mat I have on my truck bed and go skiing. The batteries are only $83 each at Costco. Cheaper to replace than spend my time obsessing. Thanks for talking the newbie down.