Wiring question about WirthCo 20092 Battery Doctor 125 Amp/150 Amp Battery Isolator

[jacks18614]

Since my new truck uses a quart of fuel per hour I am going to use the vehicles engine for AC and heat when needed as needed with the transmission in park at idle.


The wiring diagram for subject device shows house battery going to chassis ground. I really don't want to drill another hole in the truck body.

Using 4 Gauge Premium Extra Flexible Welding Cable 600 VOLT COMBO PACK - BLACK+RED - 15 FEET OF EACH COLOR - EWCS Branded can I run the negative cable back to the starter battery and use that existing ground?

What size blue sea fuse should a use (150A?) and due to them being sold two to a package where would the preferred placement of both fuses?

 

[Trebor English]

The point of the fuses is to protect the wire between the two batteries.  You want the fuses as close as possible to the sources of high current, the battery plus terminals.

According to the wikipedia chart #4 wire is good for 70 to 95 amps continuous duty depending on the insulation temperature rating.  Since this application is most likely not going to have a high current overload other than a chafed wire short circuit I would use the fuse size that is the next size larger than 95 amps.  That's likely 100 but I haven't gone shopping.  The next ten people will have ten different opinions on fuse size.  

My experience with idling engines is that they overheat.  Before extended idling try it under close supervision.  Having the hood open helps.  I wouldn't do that without an automatic over heating shut off.

 

[Weight]

Your cable insulation (105c) can safely carry 130 amps inside the engine space, 160 in open air. I don't know what your alternator can produce, but 15 feet times two, that wire gauge will have it's maximum 3% voltage drop of at less than 50 amps. I size charging circuits for 1% voltage drop, but that's me. You need a fuse at each positive battery terminal. I would use 130 amp fuses. Again, to have the least voltage drop while protecting the wire. And yes, you can run a negative return cable between the two batteries, negative to negative.

 

[jacks18614]

Maximum Alternator Capacity (amps), 150,

500 Cold Cranking Amps, 50-amp-hr maintenance-free battery

3% drop of 13.8=13.38=I can live with that

 

[highdesertranger]

you are going to idle your main engine for hours? highdesertranger

 

[jacks18614]

!0 mins per every half hour at most. Cars in LA and NYC spend half of the time going nowhere fast,

 

[frater secessus]

Looks like there are D-RIngs and other kinds of mounts that back there. Could you back out the bolt from a mount, and reinsert it through the house ground cable lug? Still dependent on body grounding but no new holes would be required.

 

[Weight]

If your alternator actually produces 150 amps, let me use 100 amps. Even that is questionable at idle speeds. At 15 feet one way, you will have 6.38% voltage drop. 13.8V ends as 12.9. Not enough to charge a 12V deeply cycled battery. I would sooner worry about CO from the exhaust while parked. Get a detector.

 

[highdesertranger]

10 minutes every 1/2 hour means you are running your engine 30% of the time. a 150 amp alternator once it heats up will be lucky to out put 50 amps. highdesertranger

 

[John61CT]

And that assumes a stock regulator even does a half^ssed job getting deep cycled batteries charged.

Quite unlikely.

Make darn sure no leaks back into the living space, IMO buy a CO detector.

And very expensive wear and tear on that engine, a cheap quiet little genny would be much more cost-effective long-term.

Aircon is a very expensive "need" for boondocking

 

[jacks18614]

Looks like there are D-RIngs and other kinds of mounts that back there.  Could you back out the bolt from a mount, and reinsert it through the house ground cable lug?   Still dependent on body grounding but no new holes would be required.

I took possession of the TC today and there is just one Torx fastener holding down d-ring so it's just going to be one positive wire going down the pass side (exhaust is on the drivers side in a plastic loom with stick on mounts and a rubber grommet thru the hole in the floor) and a short ground run reusing the Torx bolt

 

[Weight]

For charging circuits on house battery, as well as any critical or heavy use, it is much better to have the two cables rather than a chassis negative. But if you do, make sure the attachment point is shiny clean metal. I used solder to plate the area on the chassis.

 

[Trebor English]

The stuff you get in a little tube to put on spark plug threads contains oil and fine powder of copper.  A bit of that on the threads and on the ring terminal will improve conductivity and reduce corrosion.