Sure Power Isolator to Blue Sea 7622

[Ocsmb]

Hi Greg, how did you determine that 150a fuses on both ends of the 7622-start battery cable is what you need ?

Also would I be ok with 2 gauage cable for the 7622 to the house and start batteries?

FYI - I have a DC Power 185amp alternator, qty 2 Kyocera 80w solar panels, and Charge Wizard for the house battery. Plan is to install Blue Sea 7622 under the couch and hook up to the house battery and the 2nd start battery that's stowed next to it under the passenger side floor much like Vo described in the OP. Typically I just use the larger size fridge, house lights, porch light, water pump, propane furnance, propane water heater and 12v plugs when camping.

[boywonder]

Originally Posted by Ocsmb

Hi Greg, how did you determine that 150a fuses on both ends of the 7622-start battery cable is what you need ?

Also would I be ok with 2 gauge cable for the 7622 to the house and start batteries?

Well......I'm not Greg.....but:

The fuse/circuit breaker needs to be small enough to protect the wire it's connected to in the event of a short (like battery cable rubbing against the frame)...you don't want a battery cable bursting into flames....

but.....

Also (hopefully) allow the house batteries to start the van if needed....this is a little tricky, since you usually need 100's of amps to the starter to turn the engine over. This requirement means large breakers and fat cables. These amps are the cold cranking amps (CCA) that the starting batteries advertise...like 700CCA

Protecting the cable is why you want to wire the breakers/fuses close to the batteries.

All that said, I'm running 2AWG cables and 150A breakers and I figure worst case is I'll have to sit and let the house batteries charge up the starting battery for say 15-30 minutes if I'm stuck. Hopefully without engaging the starter the current between the banks will be less than 150A. Once the starting battery has enough charge turn the key and be on your way.....

I have a 5.4L so it'll probably turn over with a D cell compared to a diesel.

The current though the breakers is really a function of the state of charge of the battery banks.

[Ocsmb]

Thanks Boywonder

[Scalf77]

I am a big user of the blue sea circuit wizard, Circuit Wizard - Blue Sea Systemsso I generally input my data into that and see what the results are.

This is the data I used for my calculation

V10
Alternator 130 Amps
Starter motor normal load current draw 130-220 amps Max 800 amps
Starting Battery CCA 750
House Battery CCA 1595 1 -4D Lifeline
Note: the CCA is important for choosing the correct AIC rating for your fuse.

Length of wire from Start Battery to ACR 12 foot one-way or 24 calculated for full circuit. (The wire size will be impacted by your voltage drop setting, for this I set it to 5%, normally I would choose 3% or less it depends on the circuit and equipment)
Wire is rated for 105 C (this is important for your ampacity rating

There are derating factors you can put into the calculator, these are also important because they are going to have a big impact on calculation.
For this circuit I chose engine room, because a good section of the wire runs in the engine compartment and thus is subjected to heat. Lesser ones, that I checked in this case is wire in sheathing, and terminated at fuse, both of these cause extra heat but the engine room is the big factor here.
I generally set the load as variable, this covers surges
I also set duration to 10 mins, (I don’t really every expect to pump 130 amps through here for 10 mins)
Next for fusing I use the 1595 CCA spec for my 4D house battery, I choose main for the circuit, technically the one on the ACR could be considered a branch, but I am using the same fuse in both locations, this setting will require you to have a higher AIC rating for your fuse.

Circuit Wizard Input



Circuit Wizard Results


I apologize it is a little hard to read the fuse rating, but is says 150 amps shows the fuses or breakers that cover the AIC rating. I use the terminal fuses.
So the gap, like Boywonder said is in the jump starting, I am in the ball park for normal load of the starter, 130 – 220 amps. I expect that this will be like jump starting, where your starter is low, not completely dead, so I am comfortable with that. Also it hopefully would not be for a long duration.

-greg

[Flux]

Nice Link. I wondered about a fuse that might allow you to put some CCA back at the starter from the house battery if the starter battery was dead. Like a Slow Blow type fuse that would let momentary high amps back through. I work in commercial outdoor lighting and many LED drivers have a big inrush current that blows fuses. Slow blow solved these issues.

Then use quick fuses for all your house loads from the house battery. Unless you are feeding an electric motor, there shouldn't be too much of an inrush.

Really though, I suspect that all you guys carry some tools and could pretty easily bypass any fuse and get the house battery on the starter in short order if necessary. Just combine terminals on one lug and let it rip.

What kind of amperage to these batteries draw when they are drained?? I suspect it's not an open tap really, but I honestly don't know.

[Scalf77]

So the fuse I use has time delay of about 180% at 10 seconds. So I have 270 amp at 10 seconds. The normal load for the starter is 130 -220, I can hold 270 for about 10 seconds, so I really am not worried about jumping it with the house if needed.

So if you short the lifeline 4D to ground , you can produce 1595 amps at 68°F ( it goes down with temp) . This is why when looking for a fuse, even though I spec a 150 amp fuse, I also have to look at the IC or (Interrupt Capacity). The interrupt capacity is the value of current the fuse can open and break the circuit.

-greg

[Flux]

Good info there and thanks! What kind of fuse did those curves come from??

I appreciate the help with this stuff, I have a lot to figure out but that's some of the fun with this. I really need to get a wiring plan in order and start sizing these things out. I messed around with that circuit configurator. It certainly is helpful.

I am all in on the blue sea 7622. It's a nice piece and I like the remote.

[Ocsmb]

Thanks for the link and explanation Greg. I noticed on the Blue Sea 7622 install diagram there's a comment box pointing to the fuse near the start battery and another near the house battery on the cables leading to the 7622, note states "USE circuit protection only if ACR is not used for emergency cross connect."

[boywonder]

Originally Posted by Ocsmb

I noticed on the Blue Sea 7622 install diagram there's a comment box pointing to the fuse near the start battery and another near the house battery on the cables leading to the 7622, note states "USE circuit protection only if ACR is not used for emergency cross connect."

.....Probably assumes worst case......dead starting battery and lots of cranking amps required...freezing cold morning.....that could easily exceed 150A.........or whatever ampacity breakers that work for protecting the cables.

[Scalf77]

Originally Posted by Ocsmb

Thanks for the link and explanation Greg. I noticed on the Blue Sea 7622 install diagram there's a comment box pointing to the fuse near the start battery and another near the house battery on the cables leading to the 7622, note states "USE circuit protection only if ACR is not used for emergency cross connect."

Originally Posted by boywonder

.....Probably assumes worst case......dead starting battery and lots of cranking amps required...freezing cold morning.....that could easily exceed 150A.........or whatever ampacity breakers that work for protecting the cables.

Agreed, in the test they actually say "If the ACR is to be used for cross connect, fuses between ACR terminals A and B and each battery positive are not required according to ABYC guidelines."
If the primary use of this circuit in my van was emergency start I suspect I would go that route, in reality my primary use is use the alternator to run stuff connected to the house, and bulk charge house battery while driving. I rarely combine the two when I am charging from shore power or solar even.

I had this happen in my vans early life.


They was no fuse on the battery side of that cable, when left on shore power and charging the only thing would happen is the charger would get shut down. The annoying thing is the process of me getting into the van and probing around made this difficult to find, because this was rubbing against the frame.

In my use, I am the ACR is after the main House Battery fuse, and that won't get removed. The 150 on the side of the ACR to the battery could get removed, as it is somewhat redundant, although I am going to from one size cable to a smaller cable. The fuse at the starting battery would be the main issue.

If emergency start was my primary goal, I would alter my layout and put the ACR directly between House and Starter. The connection to the house would be before the main House circuit fuse. Note (Sportsmobile does not fuse at the house battery).


So you can certainly do with out if you are comfortable with that. Also I don't know the specifics of a diesel starter, so you would have to adjust to that also. if you don't put them in, you would be no worse then how they come from sportsmobile.

-greg