Battery Isolator Location?

[Nailhead]

I have a positive cable running to the back of my IH project truck that I want to use to charge the 2 group 31 AGM's that I'll be using for house power, and I want to install an isolator. The cable was installed for for fire-fighting equipment (power hose reel, I think), is connected to the starter + terminal, and is pretty substantial (bigger than 10 ga), though I don't know the actual AWG.

Should I install that isolator (I have my eye on a Victron FET) near the alternator or in the battery box (Buyer's underbed box)? The box location will be essentially weatherproof, which I'm assuming is preferable for the isolator (can't find any reference to IP or the like in any online Victron documentation) unless it's preferable to locate it near the alternator.

As you can see, I could use some help in this matter.

Or maybe I'm just overthinking it.

 

[Herbie]

Knowing the actual gauge of the cable will help you decide, but if it's really only a little bigger than 10-gauge, maybe better to use that as a signal wire or for running power to a single accessory. Blue Sea can help you calculate the needed gauge: http://circuitwizard.bluesea.com/

The bigger concern is that it's a single cable. While technically you can use the chassis for the ground path, most experts don't recommend it. It might be better to run your own cables as needed. When I did this on my van, the most cost-effective solution was to cut the clamps off a set of 2-gauge jumper cables. Welding cable is also a good solution.

I used such a big gauge because I wanted self-jump capability and I wanted to be able to tie-in the house batteries if/when I ever got a winch installed.

 

[broncobowsher]

Location in the circuit doesn't matter. Anywhere between the 2 batteries will do. Environmental considerations can be an issue. How will you be actuating this isolation? Switched ignition power? That probably makes more sense to have the isolation up near the front so you have a short run of switched power.

 

[llamalander]

Mounting the isolator next to one battery or another can help you fuse it cleanly. Both Batteries should have a fuse/breaker on the connecting cable.
Having the isolator next to the starter with a breaker to shut it off can make work on the vehicle a little easier when your positive can be energized from both ends-

 

[OllieChristopher]

Hi there, I don't think it matters how close to the batteries the isolator is. I would just find a convenient spot that makes it easy to access. If you have not purchased it yet you might want to consider a Blue Sea 7622 ML ACR automatic charging relay.

As stated by Herbie I would be concerned of a single wire as well. Best bang for the buck (if running a ML ACR) is to run 1/0 wire power cables from start battery to alternator to ACR to house batteries. And link house batteries with 1/0 as well.

For ground you do 1/0 from engine block and chassis to start battery. Then from start battery directly to the house batteries. Without seeing what size wire you have I can tell you the minimum I would go (if 1/0 is cost prohibitive) is the same size as your starter wire. Most starter wires on full size trucks are at least 2 AWG.

For fusing there are a lot of options. I found the easiest to work with are the Blue Sea Terminal fuses. Cheap and easy to install, access, and change. You will need one at each positive terminal of the starter battery and incoming house battery to relay.

I'm not too keen on using diode isolators due to voltage drop and only one direction of current flow. Both ACR's and diode isolators have pros and cons. The choice is yours......

Let us know how it works out whatever you choose. There are so many options for what you are doing it is mind boggling.

 

[broncobowsher]

Before you use the chassis as a ground, inspect the factory ground and see if it even contacts the chassis. Many vehicles the only items with a good ground is the body and the engine/transmission/alternator/all that metal all bolted together.

The chassis often has no ground or just a light ground for radio noise. The body sits on rubber mounts, the powertrain also sits on rubber mounts. Almost 25 years ago I learned the hard way about trying to use the frame as a ground. Installed a winch, chassis ground. Hit the winch button, puff of smoke as the little 18 gauge gas gauge sending unit ground wire (the sole chassis ground) tried to be a light bulb. Fixed the wire, got the gas gauge working again. Moved the winch ground to the engine block.

 

[vtsoundman]

Install the proper sized ground straps and cable between battery and engine. Problem solved.

It is highly recommended to install big cables b/c so many folks never upgrade the batt to chassis, motor/alternator to chassis, body to chassis, etc...

Sent from my Pixel 4a using Tapatalk

 

[broncobowsher]

Install the proper sized ground straps and cable between battery and engine. Problem solved.
...

And missed it by a mile.
Chassis still isn't grounded even if you add a ground between the batter and the engine.

Just goes to prove that people that know things still miss the basics. I had to smoke a wire to learn that lesson. Others will have to suffer before they learn as well. Just trying to limit the suffering.

 

[vtsoundman]

And missed it by a mile.
Chassis still isn't grounded even if you add a ground between the batter and the engine.

Just goes to prove that people that know things still miss the basics. I had to smoke a wire to learn that lesson. Others will have to suffer before they learn as well. Just trying to limit the suffering.

Hmmm...yes I missed it in the first statement, but caught it in the 2nd. Said ground motor/chassis. If all the connections between battery, engine, chassis, and your load (assuming it is connected to chassis,), you should be fine. If it isn't and the return is still finding another path, you have too much series resistance. That being said, anything over 60-80A, I'll run a dedicated return.

Sent from my Pixel 4a using Tapatalk

 

[Nailhead]

Knowing the actual gauge of the cable will help you decide, but if it's really only a little bigger than 10-gauge, maybe better to use that as a signal wire or for running power to a single accessory. Blue Sea can help you calculate the needed gauge: http://circuitwizard.bluesea.com/

The bigger concern is that it's a single cable. While technically you can use the chassis for the ground path, most experts don't recommend it. It might be better to run your own cables as needed. When I did this on my van, the most cost-effective solution was to cut the clamps off a set of 2-gauge jumper cables. Welding cable is also a good solution.

I used such a big gauge because I wanted self-jump capability and I wanted to be able to tie-in the house batteries if/when I ever got a winch installed.

Thank you for the reply. I'll know this weekend what size that wire actually is. I like the the idea for powering a winch, I'll make a mental note of that (even though I don't have space for a bumper-mount winch, and don't have the back for a receiver-mount one).

Location in the circuit doesn't matter. Anywhere between the 2 batteries will do. Environmental considerations can be an issue. How will you be actuating this isolation? Switched ignition power? That probably makes more sense to have the isolation up near the front so you have a short run of switched power.

Thank you for your reply-- I'm assuming the switched power would be necessary to start the alternator? I have a GM-style 10si single-wire, with a "BAT" terminal on it which I would assume would be the one you're referring to?

Mounting the isolator next to one battery or another can help you fuse it cleanly. Both Batteries should have a fuse/breaker on the connecting cable.
Having the isolator next to the starter with a breaker to shut it off can make work on the vehicle a little easier when your positive can be energized from both ends-

There's plenty of room under the hood, so that would be an easy location for isolator mounting. Thank you!

Hi there, I don't think it matters how close to the batteries the isolator is. I would just find a convenient spot that makes it easy to access. If you have not purchased it yet you might want to consider a Blue Sea 7622 ML ACR automatic charging relay.

As stated by Herbie I would be concerned of a single wire as well. Best bang for the buck (if running a ML ACR) is to run 1/0 wire power cables from start battery to alternator to ACR to house batteries. And link house batteries with 1/0 as well.

For ground you do 1/0 from engine block and chassis to start battery. Then from start battery directly to the house batteries. Without seeing what size wire you have I can tell you the minimum I would go (if 1/0 is cost prohibitive) is the same size as your starter wire. Most starter wires on full size trucks are at least 2 AWG.

For fusing there are a lot of options. I found the easiest to work with are the Blue Sea Terminal fuses. Cheap and easy to install, access, and change. You will need one at each positive terminal of the starter battery and incoming house battery to relay.

I'm not too keen on using diode isolators due to voltage drop and only one direction of current flow. Both ACR's and diode isolators have pros and cons. The choice is yours......

Let us know how it works out whatever you choose. There are so many options for what you are doing it is mind boggling.

Care to elaborate on the pros & cons of both ACR's and FET isolators? To be clear, I am NOT looking at diode isolators as an option; the Victron FET unit looks like a better option, and it's pretty much the only isolator I have in mind (don't know of any other brands, getting tired of researching after 2 1/2 years of building this...). I looked at the BS ACR, and came away wondering what advantages it would confer. I also checked out those fuses, and didn't like the way their fuse blocks eliminate the top posts on my batteries as connection options. The flat-mount breakers I found at Remy Battery seem to me to allow more options for connection. You got me thinking, though, and I can't thank you enough for that.

Before you use the chassis as a ground, inspect the factory ground and see if it even contacts the chassis. Many vehicles the only items with a good ground is the body and the engine/transmission/alternator/all that metal all bolted together.

The chassis often has no ground or just a light ground for radio noise. The body sits on rubber mounts, the powertrain also sits on rubber mounts. Almost 25 years ago I learned the hard way about trying to use the frame as a ground. Installed a winch, chassis ground. Hit the winch button, puff of smoke as the little 18 gauge gas gauge sending unit ground wire (the sole chassis ground) tried to be a light bulb. Fixed the wire, got the gas gauge working again. Moved the winch ground to the engine block.

I figured that one out over 30 years ago after burning the throttle cable off an old Abarth. There is a brand-new 2 AWG ground cable from the battery to the engine, and from the engine to the frame rail. BTDT. Thank you for the reminder, though.

Install the proper sized ground straps and cable between battery and engine. Problem solved.

It is highly recommended to install big cables b/c so many folks never upgrade the batt to chassis, motor/alternator to chassis, body to chassis, etc...

Sent from my Pixel 4a using Tapatalk

Got 'er-- see above. Thank you.

Hmmm...yes I missed it in the first statement, but caught it in the 2nd. Said ground motor/chassis. If all the connections between battery, engine, chassis, and your load (assuming it is connected to chassis,), you should be fine. If it isn't and the return is still finding another path, you have too much series resistance. That being said, anything over 60-80A, I'll run a dedicated return.

Sent from my Pixel 4a using Tapatalk

That 60-80A figure catches my eye because I don't think I'll ever run nearly that much through the charging circuit. I'll have a generator to run 35A inverter/charger and a 200W solar suitcase to handle battery charging, so if that bone-stock 10si alternator doesn't finish charging the batteries while driving, I can conceivably top them off ofter arrival.

 

[broncobowsher]

IF that is a 1-wire alternator as you describe, the BAT terminal is just an output, connected straight to the battery.
By a switched power I am referring to so wire that only has power when the engine is running. That BAT terminal on the alternator is always hot since it is connected to the main battery. I am refering to something that is only active when the engine is running. That way when it is off, it is isolated. Not even the accessory position as that can be left on while listening to the radio and run things down. There are so many ways it can be done. Even an oil pressure switch so the relay is only energized when there is oil pressure. Presumably the only time there is oil pressure is when the engine is running. Most windshield wipers are only active with the key in the run position. Stock alternator turn on wire. EFI fuel pump. The options are there. Just how do you want to do it.

 

[Nailhead]

IF that is a 1-wire alternator as you describe, the BAT terminal is just an output, connected straight to the battery.
By a switched power I am referring to so wire that only has power when the engine is running. That BAT terminal on the alternator is always hot since it is connected to the main battery. I am refering to something that is only active when the engine is running. That way when it is off, it is isolated. Not even the accessory position as that can be left on while listening to the radio and run things down. There are so many ways it can be done. Even an oil pressure switch so the relay is only energized when there is oil pressure. Presumably the only time there is oil pressure is when the engine is running. Most windshield wipers are only active with the key in the run position. Stock alternator turn on wire. EFI fuel pump. The options are there. Just how do you want to do it.

It is most definitely a 1-wire GM-style 10si alternator, as mentioned previously.

I am very familiar with a switched power circuit, having wired many over the years including several on this present project (additional fuel pump, Vintage Air A/C, etc.). I was referring to the alternator ENERGIZE terminal on a Victron isolator.

 

[eugene]

And missed it by a mile.
Chassis still isn't grounded even if you add a ground between the batter and the engine.

Just goes to prove that people that know things still miss the basics. I had to smoke a wire to learn that lesson. Others will have to suffer before they learn as well. Just trying to limit the suffering.

I'd have to guess the previous owner of your vehicle removed the large ground as I've never seen a vehicle without it. My first truck was like that, previous owner put o a body lift and the large ground didn't reach so they left it disconnected. I found out years later when the large battery to engine block connection rusted so current went through battery to body to frame to engine and burned the remaining small wire. So I had to fix the battery to block and reconnect the large battery to body wire, apparently when dad removed the body lift he missed it.

 

[eugene]

Does your vehicle have a factory jump start terminal? I know a lot of them have went to that to steer people away from connecting cables directly to the battery. Mine mounted off the side of the engine sort of between the alternator and battery and three cables meet there, one coming from the alternator, one going to the starter and then one going to the battery. So it made a good spot right next to it where I could simply move a cable over if needed. I've had both an isolator and a separator there. Bolt rusted and broke off the isolator and I just replaced it with the smaller/cheaper separator, but the location worked well for either.

 

[Nailhead]

I'd have to guess the previous owner of your vehicle removed the large ground as I've never seen a vehicle without it. My first truck was like that, previous owner put o a body lift and the large ground didn't reach so they left it disconnected. I found out years later when the large battery to engine block connection rusted so current went through battery to body to frame to engine and burned the remaining small wire. So I had to fix the battery to block and reconnect the large battery to body wire, apparently when dad removed the body lift he missed it.

The previous owner was a fire department in Arkansas, and it was missing its engine-to-frame ground, IIRC. It's been 2 1/2 years since we did the teardown on it, so I don't remember clearly. It does, however, have a 2AWG ground in that spot now.

Nice-- the Simpson Method: "It doesn't reach, so it's not worth doing".