Need help choosing appropriately-sized battery isolator and batteries

Discussion in 'GM Electrical Tech' started by SurrealOne, Sep 1, 2011.

  1. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts


    I am not an electrician but am comfortable doing most work so long as a manual and the Internet are handy, as I research heavily and go slowly/methodically when learning something new. As prep for upcoming stereo, light, and winch installations in my 04 Sierra I'm queuing up the following work:
    • Upgrading my 105amp alternator to a 240amp (dcpowerinc) alternator
    • Changing my serpentine belt to that which is used with the 145amp alternator (this is what dcpowerinc recommends)
    • Replacing my starter battery with a Sears DieHard Platinum P-4 [Size Group 34/78] - this is a rebranded Odyssey battery!
    • Adding an auxiliary battery (another Sears DieHard Platinum P-4) in the usual location
    • Adding a battery isolator so that accessories using the auxiliary battery stand no chance of discharging my starter battery
    • Wiring batteries, alternator, and isolator using 2GA wire (and yes, I'll solder) for positive and ground connections (effectively a 'Big 3' upgrade); 150 amp in-line fuses will be used where appropriate
    • Adding a fuse block off the auxiliary battery to allow for easy future connections (stereo and lights; winch will term on the battery posts) to it
    I have three questions:
    1. Can I fit a bigger DieHard Platinum in both locations? If so, what group size have others slotted in each location successfully?
    2. What battery isolator will suit this alternator best? I'm contemplating this one but would like a nod from someone a bit more electrically-inclined than I am: (It handles 240amp peak load and I've confirmed the alternator is considered a 'group 1' alternator on this chart: I'm open to suggestions...
    3. Does anyone have cable, inline fuse holder, and fuse block recommendations? I know some people use welding cable but I want something more tightly-wound for flexibility and to help reduce corrosion (less exposure to air with a tighter wind).
    Please advise.

    Last edited: Sep 1, 2011
  2. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    The isolators that I've seen knowledgable and trustworthy members reccomend in the past are the isolators from HellRoaring ( I'm planning on getting one when I upgrade my electrical system.

    As for wiring, you have a couple options: car audio power wire and welding cable. Both essentially are the same thing, a cable that is composed of many hundreds of thin-gauge wires bundled together into 1 large cable. The advantages are two-fold: first, looking into our electrical theory manuals, electricity actually moves on the surface of metals, so by having many small conductors, the surface area increases and therefore carrying capacity. The second advantage is that the wire is pretty soft and pliable so it's easier to route. The main difference between the 2 is the colored jacketing and price. I'll be using welding cable...

    It looks like you're going to want at least 4 gauge when wiring up everything.
  3. wayned

    wayned Rockstar 100 Posts

    I used a pac 200A isolator $50
    flat blade fuse $10[​IMG]


    Last edited: Sep 2, 2011
  4. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Hrm. I came across the Hellroading gear when I was searching. Some facts:
    • The 75150 is only rated for 75 Amps continuous and150 Amps peak (20s duration w/ 5 mins required between peak uses).
    • The 75150 is a big fat 'maybe' on Hellroaring's matrix in the row for usability with a 200 Amp alternator.
    • The specs for the Hellroaring 75300 are not listed on Hellroading's site but it CAN be used with a 200 Amp alternator.
    • Specs for the 95150 were also not available but the 95150 instructions state "Isolation on the Auxiliary battery side requires that deep cycle loads not exceed the BIC rating if the alternator output is rated at 90 amps or higher".
    • The 95300 is rated for 170 Amps continuous and 300 Amps peak (20s duration w/ 5 mins required between peak uses). This is suitable for my purposes but is larger than actually needed. (I'm looking for 120 Amps continuous and 240 Amps peak.)
    Hellroaring claims the following of its 75150: "Probably the best connection method is to connect your starting battery only to your starter circuit. Then isolate this circuit from all other loads and your deep cycle battery using the BIC-75150A. A starting battery rarely accepts more than 60 amps from an alternator. The BIC-75150A can handle this very well. And since all your accessory loads and deep cycle batteries are connected directly to your alternator, you can use any size alternator! A 300+ Amp alternator will not affect the BIC-75150A battery isolator / combiner when connected in this way!"

    The wiring they showed to go with that claim is NOT how I'm looking to connect the batteries to the system. I find it interesting that the basis for this claim is the starter battery not accepting more than 60 Amps. Can someone more educated than I am about alternators tell me why this is?

    The PAC's technically not an isolator, it's a relay (that can be used for isolation), yes? (i.e. It uses solenoids not diodes.) I dug up specs on it and it looks like the 200 is rated at 200 Amps continuous and 310 Amps peak. That's hefty at a very affordable price ... but it sacrifices some of the longevity/reliability of a diode-based system. It also DOES NOT have the traditional voltage drop that most (diode-based) isolators have. (That's also where Hellroaring seems to shine -- little voltage drop.)

    I'll have to do some more reading, but I think the PAC is looking very appealing. I'm curious how the largest Hellroaring compares., price-wise.

  5. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Interesting find! How much did the single rectifier set you back and what is the measurable voltage drop imposed on the system? (I'd likely purchase a dual rectifier, but I'm trying to get some idea of pricing before calling them...)
    Last edited: Sep 5, 2011
  6. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    Thanks for the find on Power Gate isolators. I had a good discussion with Scott at Pefect Switch, LLC today. He answered every question I had ... and then some. Ultimately I pulled the trigger on a 300 amp dual rectifier. The blend of super low voltage drop, high sustained amperage purchase options, and significantly higher than usual peak amperage capabilities (per option) are the things that sealed the deal for me.

    For others who are curious, the Power Gate isolators can be found at this site: There's a reason you don't see prices on that site -- they are VERY pricey. (The 300 amp dual rectifier I bought was nearly 400 clams. Owww!) However you get what you pay for, as the units are MOSFET switches (that produce negligible voltage drop), are waterproof, are heavily tested, and are military grade. This is about as close to a bomb-proof isolator as you'll find...

    Note: 300amp was chosen because the 240amp alternator' rating is for continuous output; supposedly it can output yet again more. This also meant 300 amp ANL fuses for the links from the rectifier to the batteries in order to protect the wires.
    Last edited: Sep 13, 2011

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