Bigfootchevy
Bancroft, Ontario, Canada
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I don't know for sure if this is true or not but I was told that Ford installs a battery isolator on their HD Trucks. I know for a fact that GM does not.
If it didn't have an isolator, I believe both batteries would be dead. That's what happens on my GM anyway.
Paul
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mark_be
Belgium
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snowcrustracer wrote:More than likely the camper has a battery separator that will protect the camper battery when the truck battery drops below 12.8V
I've tested this today and I'm affraid I have to say that it doesn't have it. I disconnected the camper from the truck and used the camper battery until it dropped to 11.8V and still received that voltage at the connector.
That's exactly what I don't understand: there is nothing to disconnect, but how is it possible that the camper battery stays 100% if the truck gets to 20%? 
EDIT: maybe it's protected one-way? If it is, isn't it protected the wrong way then?
2001 Ford F350 7.3 Diesel (DRW Crew cab Long bed)
2011 Arctic Fox 992
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Chuck and Di
Ontario, Canada
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Given it was installed by a dealer, and more likely by a trained monkey employed by the dealer, the circuit could be almost anything AND almost anything with errors. You will have to trace all the wires to get a complete circuit. Your best bet is to ask the dealer for a circuit diagram of what they did, then if it makes sense, hunt the error - if indeed there is one.
Shipping it with everything connected and powered up certainly shows they are not the brightest bulbs in the box since the various alarms on a new camper (CO, propane, etc.) will pancake pretty much any battery combination in a couple weeks without a recharge, so you are right to be suspicious with the truck flat and the camper fine.
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AnEv942
CA
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mark_be wrote:snowcrustracer wrote:More than likely the camper has a battery separator that will protect the camper battery when the truck battery drops below 12.8V
I've tested this today and I'm affraid I have to say that it doesn't have it. I disconnected the camper from the truck and used the camper battery until it dropped to 11.8V and still received that voltage at the connector.
That's exactly what I don't understand: there is nothing to disconnect, but how is it possible that the camper battery stays 100% if the truck gets to 20%?
EDIT: maybe it's protected one-way? If it is, isn't it protected the wrong way then?
your test is wrong side-If it had a battery isolator what you show is correct. Camper battery drained -its open to accept charge.
What should happen now (if camper has isolator to protect TRUCK) is if you plug in camper to truck, which you could check now youve drained camper batts.
1 Check truck batts voltage before & watch, Plug into truck-camper shouldnt drain truck trying to recharge. If truck off, not charging and its batts below 12.8, power shouldnt flow. If it continues to drain truck past 12.4 (or what ever standing volts were) no isolator. (note: no idea what standing volts/condition current truck batts are)
2 Truck is running/charging and its batteries are over thershold voltage 12.8?, power would flow into camper batts charging them.
3 If you dont have an isolator its going to drain off truck period. (got charger handy)
As far as testing volts and connectors- the truck side of connectore is 'hot' wired to battery you will always see voltage at bed connector. (bad imho)
At the camper pigtail I would also expect it to show voltage-even if it had a isolator-its monitoring-its not going to show if 'isolator' is allowing flow, as I understand it anyway.
To many variables here and non eliminated...seem to be chasing tails.
-I would verify with dealer or manufacture what camper has or doesnt.
-I would verify that coincedently truck doesnt have a failing battery or other problem/drain totally unrelated to camper
-I would verify truck has or doesnt have trailer charge line (never confirmed if it does or not).
-Wether camper has or doenst an isolator- my primary concern is to protect truck. If truck has relay controlled charge line I would at minimum remove the wire going directly to truck batt and splice into relay controlled charge line.
If truck doesnt have relay controlled charge line or to utilize larger new wire Id add an ignition controlled solinoid to positivley dissconnect truck from camper (even if camper has an isolator)
Lastly dont take camper battery down that far any more.
spell off
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joerg68
Ueberherrn, Germany
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Hi Mark,
I second snowcrustracer's suggestion. Go hunting for that separator he mentioned. It looks just a plain old square black plastic box, about 5cm by 5cm. I have one in my Lance and it works jsut fine. It must be near the 12V fuse box, I would think. You may also try to talk to Adventurer about it.
BTW, I have read about cases where the wiring to the separator was reversed by the factory. Your case does not sound like that, though.
Here is some info on the separator and its operation:
http://www.cooperindustries.com/content/........es/instructions/BUS_CBT_INST_180126a.pdf
The truck battery can definietly run low after some time. The battery may be damaged, especially if this has happened before and / or it is more than 2-3 years old. I had to replace the battery in our '08 Silverado a few weeks ago; wouldn't hold the charge for more than a week any more.
Where did you measure the +12V in the camper?
The wire is not installed very professionally, as others have said. You need to protect it from sharp edges. At least they put in a fuse near the battery. But I do think the dealer did the right thing by running a separate lead. The gauge of the original trailer wiring is usually not suitable for charging.
Best wishes,
Joerg
"Pickups are very handy cars. One step on the brakes, and everything you need is right behind you!"
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mark_be
Belgium
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The last test is that I measured the wire just before it connects to the truck battery. That's after I disconnected it, btw. 
So this way it doesn't matter where the isolator would be installed - in the truck or in the camper - I should get zero volts at some point while discharging, because the isolator should, well...isolate, at some point. That doesn't happen, even till 11 volts. This makes me pretty sure it doesn't have an isolator.
In the beginning of this topic I started with why can the truck battery discharge without the camper battery if there's no isolator. Well, I found out that the battery led-readout in the camper sticks to "good" for way too long. If I remember correctly the read-out stays "good" until 10.5 volts or so...
That has been the reason why I THOUGHT the camper battery wasn't discharged. So I can definitely say that there is no isolator, that both truck and camper battery were discharged and that the battery readout was wrong. The batteries were strong enough to use the slide-out, but too weak to start the engine.
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mark_be
Belgium
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Another item that looks important to me:
Is there something in the truck or camper that prevents the charging current to the camper battery getting too high? It's only a small wire that connects both batteries and if there's nothing preventing high currents, it can easily go up to 100 amps (there's always some resistance in the wire and connector). The wire heating because of this current can cause fire!!
That's definitely the case if the truck batteries are fully charged and the camper battery is fully discharged, because you get both the truck batteries AND the alternator that provide the power to charge the empty camper battery. After all, batteries are in a way like communicating vessels...
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joerg68
Ueberherrn, Germany
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Mark,
the only things that limit the charge current are the fuse in the +12V line near the battery and the wire gauges of the positive and negative wires. If the wire is too thin to carry 30 Amps, it will get hot and eventually melt the insulation or even start a fire. The 30 Amp fuse ensures that this does not happen (provided the wire gauge is thick enough).
What happens in reality is - Ohm's law kicks in:
http://en.wikipedia.org/wiki/Ohm%27s_law#Temperature_effects
current is high -> wire heats up -> resistance goes up -> current comes down and stabilizes along with the temperature.
It is sort of self-limiting ;-)
Best regards,
Joerg
Edit: This is, btw, the reason why them car hifi people use those ridiculous wire gauges. The maximum output power of an amplifier is limited by the voltage that is fed to the amplifier. If the wire is too thin, the voltage can drop significantly. Especially when the load is high - which is when you would need the power most. So they use a wire gauge that can comfortably supply the maximum current needed by the amp.
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AnEv942
CA
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Cool, Perseverance-puzzle solved. So all batts were actualy approx same state-just using extreme tests (huge demand and false meter reading) at either side of charge line that led to seemingly obvious but inacurate conclusion. Interesting
Our 7.3 diesel uses ALL of both batteries to start-wont start on 1 which I recently discoverd when I had 1 of the starting batts fail. Also below 12.1 volts wont start, but then again our slide balks too. I dont use slide or jacks unless the engine is running or another power source but thats besides the point.
Now that you 'get' what actually happened & solved the puzzle just need to address how you want to isolate camper & truck.
Might also consider something to better see actual camper battery state since led meter (typ) is so misleading. Really not good taking the batts that far down.
Good luck
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mkirsch
Rochester, NY
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Unless the battery in the camper is WAY low, like down in the single digits, you won't get an excessive current flow through the wiring.
Amps is a function of the difference between the charger voltage (i.e. alternator) and the battery. The closer the voltages, the lower the current flow.
2002 Chevy 3500 DRW 8.1L/Allison
2000 Palomino B1500
...and the reason why I need a DRW to haul a Palomino:
2004 United 7x14 tandem axle enclosed toy trailer
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