Tip to protect your batteries

DavidM · July 29, 2020, 09:41:43 AM

I had backed into a state park campsite yesterday that had a bit of downslope. So since we were leaving the next day and not driving our TV until then, I unhooked my coupler and drove forward a few inches so I could drop the Jack and level the camper. I left the chain and breakaway cable attached.

I noticed I had gone a little too far and pulled out the breakaway switch, so I backed up a few inches and pushed it back in to turn it off. But I got to thinking, what if I hadn't noticed it and left the breakaway switch on. So I got out my clamp on DC ammeter and measured the current draw- 0.3A off and 11.8A on.

Since I had previously ditched the breakaway battery and wired the switch to the main battery (check the archives for how and why to do this) I would have quickly run down my 70Ah battery in a few hours. If I hadn't made that switch. I would have run down the breakaway battery in an hour and since there is no way to recharge that battery it would soon be toast not to mention useless in a real breakaway.

So the moral of the story is watch that switch and immediately reconnect it if it is tripped.

David

keeena · July 30, 2020, 02:16:32 PM

0.3amps when off surprises me; that's a lot of current draw for a simple switch circuit...it really should be zero. I'm going to measure mine when i get a sec.

charliem · July 30, 2020, 04:45:58 PM

The 0.3A drain includes the CO/Propane monitor, fridge control board and maybe a gas valve and/or device chargers. Not unusual.

DavidM · July 30, 2020, 05:21:49 PM

Quote from: charliem on July 30, 2020, 04:45:58 PM
The 0.3A drain includes the CO/Propane monitor, fridge control board and maybe a gas valve and/or device chargers. Not unusual.

Yes, to all of the above except device chargers as we had just arrived at our campsite and didn't plug them in until later that night. Also I don't think the propane solenoid valve was on at the fridge as when I checked it later it was up to 0.45A.

The current breaks down approximately as follows, +/- 0.05A:

Base parasitic draw- fridge not on, but CO/propane monitor on: 0.15A
Fridge on but not the solenoid valve: 0.15A
Fridge on and solenoid on: 0.15A

Typically for all of the above plus device charging, lights, water pump use, and 15 minutes of water heater use we use 10 Ah daily if we camp with no fridge (for a night or two we just bring an ice chest) and 15 Ah with the fridge.

David

DavidM · September 08, 2020, 05:56:41 PM

I did it again, same campsite as before. This time I didn't notice it for several hours. Pulling 10+ amps on and about .4 amps off. Probably pulled down my battery by half in that period- A G24 Interstate.

David

Merlin · September 08, 2020, 08:38:08 PM

Hmmmm.......time for longer breakaway switch cable? I have a coiled one on mine that's longer than the safety chains. Just saying..........

DavidM · September 08, 2020, 10:16:51 PM

Yes early. this year I replaced the cable as the original was too long and dragged, but as you note I probably got the new one too short. Oh well!!

David

Pinstriper · September 08, 2020, 10:22:44 PM

In that case you need to guard against it activating just on sharp turns, maybe. The last thing you want is the brakes locking up, or just dragging while you are rolling down the road. Good way to overheat them and/or wear them down.

I dunno that there's a safety difference between locking the brakes up in a disconnect situation when the trailer is 12" away from your rig versus 24".

Of course, too long and it can catch/hook on road debris and activate - not good, neither.

DavidM · September 10, 2020, 11:37:27 AM

After drawing down my battery to about 60% and with two more days of camping and no easy way to recharge other than hooking up the ltrailer connector and running the TV's engine (yes I could have used jumper cables for faster charging but I was lazy) I measured the state of charge and ran the TV for a few minutes over the two day period to see what the charging rate was. These SOC measurements are roughly based on specific gravity measurements.

Day 1, 60-70% SOC, 5-6 amps

Day 2, 40-50% SOC, 7 amps

Day 3, <20% SOC, 10 amps

The numbers surprised me a bit. In years past (many years) I remember higher charging rates at 50% SOC, about 10-15 amps. I suppose it does depend greatly on the TV, its wiring size and its alternator output. The higher rates I remember were with a 2000 F150 whereas my current TV is a 2013 Nissan Pathfinder.

For the electrical types out there, even though the nominal current available from the trailer connector is 30 amps or at least it is protected by a 30A fuse, voltage drop in the wiring reduces that dramatically. With the TV's alternator putting out 13.6 V (actual measured voltage on my current TV) and at least 20' of hopefully 10 gauge wire, the voltage drop at 10 amps is 0.4 volt. So the charging voltage at the battery is only 13.2 which will only drive 10 amps into the battery. If the battery were really dead and acting somewhat like a short circuit the current would be higher since it doesn't take 13 volts in that condition to drive significant current. End of electrical talk.

David