furnace/heater question

I have a decent meter to work with. Forgive my ignorance but if the neg terminal is disconnected.. this causes an incomplete circuit.. no? So.. how will it draw current? It will attempt to draw but can't.. and can be measured?

Most multimeters can measure current. Even a free-with-coupon Harbor Freight one will measure up to 10 A (for short times - the leads aren't very heavy gauge). You just set it to amps, disconnect the ground clamp on the battery, and hook the meter between battery negative and ground. There are other places you can measure, but that's usually the easiest. Only measure one thing at a time, if you turn on more than 10 amps worth, you could blow a fuse in the meter.

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thanks for the info in replies. Was looking for rough guestimate. Not sure of amp hours on my Battery Warehouse commercial batteries. I suppose I can test in driveway. How can I test amp
draw?

You should be fine overnight with things as you describe.
But how do you plan to recharge them daily as you most likely will not get 2 nights out of the batteries

My furnace measured at 6.7 amps, so I can figure out the rest with my set up.

My furnace (Suburban NT-20SEQ) draws a measured 2.1 amps when running steady (a bit more when first starting up). Suburban specs it at 2.7 A. So, 10 hours overnight running full time would only be 21 AH.

If you have GC2 batteries, you should have ~200 AH to work with, which would give you about a week of use for furnace only. For best battery life, it's suggested to not draw lead acid batteries down below 50%, and you've got some small lighting and pump loads (fridge? that will draw ~0.5 A, even when on propane), so you should be able to get 2-3 days. And, that's for constant overnight use, so at mid-40's (guessing furnace is actually running ~3 hours/night ~= 7 AH), you may be able to go a week.

YMMV. You really need to measure how much current your camper draws with different things on.

darsben1 wrote:
Outside temp would need to be estimated.
In south Florida 2 to 3 days
In Upper Peninsula of Michigan 4-5 hours.
and this depends on age and condition of batteries.
You need to give more info

Okeedokee.. Fall camping.. let's say mid 40s at night.. want to bring temp to 68 for sleeping. Batteries are new this year.. good shape. Thanks!

I'm pretty sure the correct answer is "it depends" :) Depends on how long the furnace runs, how many Amp Hours your batteries have, how cold it is outside and a dozen other issues.

That said - the general consensus is that if you turn the thermostat down (62* or so) and it's not sub-zero temps outside, that your batteries should keep the furnace running for the night.

Outside temp would need to be estimated.
In south Florida 2 to 3 days
In Upper Peninsula of Michigan 4-5 hours.
and this depends on age and condition of batteries.
You need to give more info