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3 battery isolator or bigger alt ?

Discussion in 'Truck & Equipment Repair' started by shadow, Jan 9, 2008.

  1. shadow

    shadow Junior Member
    from iowa
    Messages: 27

    I was wondering what the general thought was about running multiple batteries or a bigger alternator. I got a 78’ chevy with a 454 and with, I assume, a factory alternator that probably puts out around 60 amps or so. I notice a big drain when the headlights are on and I have to run the plow. If I am running the up/down for around 20 min or so plowing, the headlights will almost be yellow from low power. I replaced the lights but they still go dim.

    I was thinking of getting one of those battery isolators that handle 3 batteries. Or should I get a high output alternator?

    I am thinking 3 batteries because: 1 for truck, 1 for plow power, and 1 for light bars/strobes. (I will be putting on a whelen edge bar, arrow stick, takedown spotlight, and hid-a-way strobes.)

    It is the cheapest to get the isolator but I was wondering what you guys thought about which way to go.
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Nothing wrong with running triples and a big amp alternator together...but forget the isolator, it won't work the way your thinking it will. You want to connect all three batts together to spread the amp draw amongst them all. Or else the plow would just pull the battery down that just running the plow. If you isolate them, you might as well only run one battery.
  3. streetsurfin'

    streetsurfin' Senior Member
    Messages: 770

    I have to somewhat disagree. Well maybe not disagree or argue, but present my experience with isolators...I mean I don't realy have a leg to stand on against B&B, but....I think isolators are a great idea, though you will still want a high amp alternator. 60 won't cut it. I have run an isolator on two batteries, 135 amp alternator and did several years of comercial lot, some residential and tight alley/condo/townhome plowing with no problems on the plow or truck side. I got eight years out of an optima (Plow side) red top doing so. With that set up I never noticed a low battery condition on either battery. The lighting draw was admittedly not as high. I used two seperate volt meters, rather than the dash ammeter only. The other battery (truck side) was a deka, and then an interstate. I know others who have used isolators with great results also. Those were the couple guys I plowed for before buying my own truck and plow, who schooled me on isolators. I cannot understand why so many here advise against them. I believe they are more common in this area for some reason.

    I do understand that you are assuming that he will be using the 60 amp or stock alt, B&B, and I agree that would be a poor choice. B&B, I respect you for your knowledge and help on this site. May I ask, and I don't mean this disrespectfully, have you ever used an isolator in your plow truck? Just want to further the discussion on them here since it came up again.
    In the past when I've seen advice against them, the only reason I've seen given is "they are not designed for plowing but for campers and RV's. My personal experience, is having only seen them used in plow trucks and advertised for use in the towing business, but then I haven't been around the RV community that much either. I gather your a certified tech or a man of extensive experience and am not trying to show you up. Just wondered what you had to say as to why they are not a good idea.
    Last edited: Jan 9, 2008
  4. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    Last edited: Jan 9, 2008
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No disrespect taken street..that's what were all here for...to share experience. And I do have a bit of Isolator experience so here a sample..

    The biggest problem with using an isolator in a system with a very high amp draw (like a plow) is that the currently made isolators are still not "smart" enough to do the job correctly. They are designed to isolate batteries that are under a relatively low and steady amp draw.. (like in an RV application for example). They're not designed for a high current load on the storage side (the battery) of the system of 150 amps or more for only seconds at a time. So they have a hard time "deciding" what to do with the load and current and can cause more problems than they're worth. They can be an even bigger problem on a late model truck, as when they become "confused" they'll also "confuse" the sensing field wire that controls alternator output..(some trucks do cope better than others though) which will cause incorrect alternator output. Incorrect alt output can also cause all sorts of different voltage related problems on the newer trucks. Plus the battery isolator itself isn't very efficient at transferring the current through itself and most eat 10-20 amps just controlling the charging current.Plus the Iso's themselves are a bit of a safety issue as they get hot under high demands and will short out internally..It's also tough to get an Iso rated at a high enough amperage to deal with a big amp alt under continuous duty use. I actually had one burst into flames one time due to a short on the storage side that was causing the alternator to run wide open (200 amp alt BTW) and it almost burnt the truck to the ground. So in a nut shell, they're nowhere ideal for a plow application and the safer and more efficient approach is to run the batteries all connected in parallel.

    I have experimented with multi battery/Iso set ups on plow trucks in the past and closely monitored them for advantages and disadvantages.. and after 2 seasons, I just couldn't prove that the pros out weighted the cons of running an Iso between the batteries.. I've run 2 batt 1 Iso, 4 battery 2 Iso and 5 battery 2 Iso setups on two different trucks (All these setups were for another experiment I was working on at the time, long story!) And after all this, I still had proof that running the batteries all tied together was still the best and safest setup in the long run. The only advantage I could prove 100% is that the batteries didn't have to be "matched" in order to get the maximum life and performance out of them.

    Their is hope though for an isolator that will work perfect for a plow application. Theirs a company that's designing a fully digital, microprocessor controlled, Iso that will sense and respond to the slightest current change and will be designed to handle up to a 300 amp (intermittent) current load on the storage side of the system. It is for a 12V system but won't be marketed to the auto industry (yet).
  6. shadow

    shadow Junior Member
    from iowa
    Messages: 27

    A Very informative discussion. You guys really know what you are talking about. I’m glad I posted my question. It really helps to hear from people that have had experiences with this.

    You said to connect the 3 batteries together to spread the amp draw. Is there something to put in the circuit to have them work right?

    A few years ago when I needed more power to run some inverters, I put a battery on the floor and ran jumper cables to the truck battery. It worked but I noticed each time I tested them with a volt meter, the trucks battery was around 11 volts and the battery in the cab would run around 15 volts. They were different brand batteries and one was an 850 amp and the other was a 1,000 amp. The smaller one was the one that ran high. If I run 3 batteries, couldn’t one get so over charged that it will blow? I was worried getting the 15 volt readings that the battery would boil and I would have a real mess on my hands.

    I heard about isolators after I did that setup but never got one. I saw JC Whitney had a 3 battery isolator for a sale price of $45. I have always wondered about the quality of goods from them and don’t want a fire from a cheep brand because I would have a high amp draw. I wonder if an isolator would work with just the light bars/stuff.

    I just browsed that site you linked to and never would have thought a Pontiac Transport would have a 140 amp alt. I will have to look around more on that site.
  7. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,617

    The problem with NOT using an isolator is, the weaker (ie the battery that is in worse condition or with a week cell) will draw down the good battery when the truck is sitting.

    I have a near perfect battery isolator, its called a relay. The relay is closed only when the truck is running or when I push a switch.

    I assume that when the truck is running the alternator is working, so the two batteries are connected by the relay. The switch is for when I leave something on and run the battery down I dont need jumpers, I just close the switch.
  8. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    :rolleyes:What he said:nod:
    ps do not use a relay ether or a solenoid

    Just something you do not need an something else to go wrong
    Last edited: Jan 9, 2008
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It's not necessary, simply connect them all together and forget them. Nice and simple with nothing to cause problems later. No point in adding anything between them that will create resistance in the circuit or add extra connections to corroded.

    The problem you experienced was do to the batteries being different sizes and I'm sure with using the jumper cables, didn't have the greatest connections...and both will cause one battery to charge more or less than the other. When running multiple batteries, you want the batteries to be the same size and roughly the same age (internal battery resistance increases with age). They don't need to be manufactured on the exact same day but you want them to be as close as you can to get the max life and performance from them as well as the alternator.

    Electrical parts are just like anything else shadow, you get what you pay for..:nod:

    If your going to run three batts, if you wanted you could Isolate one just for running lights and such as it would help to soften the voltage change to the lights and accessories when using the plow... but I'd still rather have all three batts running the high amp load (the plow) as this will utilize all the storage capacity you have and still help to soften the voltage drop in the system when the plow is operated.

    You shouldn't have so much difference between the batteries that you have to run a "relay" (by relay I assume you mean a continuous duty solenoid). If the batteries need to be isolated with the truck off to prevent discharging on their own, then the batteries aren't close enough in capacity or age to each other.

    And a "relay" isn't the same thing as an isolator...so it's far from "perfect" from an isolation standpoint. And like I mentioned, you shouldn't need a switch between the batteries to break the connection to keep them from discharging while idle.


    Most class 8 semi's use at least 3 batteries (some use 4) and they're all connected directly together in parallel (no solenoid or isolator between them). The truck manufactures have been wiring them like this for at least 30 years. And the battery failure and/or performance rate isn't any worse or better in them than anything else.
  10. basher

    basher PlowSite Fanatic
    from 19707
    Messages: 8,993

    Simple is better, the more un-nessacery "gadgets" you add the greater your chance of a failure. Direct wired, with identical sized batteries, installed at the same time, serviced by a high output Alt. is by far the most reliable route. If you put new batteries in when you set the system up, then change them together when needed you don't need the extra problems "gadgets" can bring.

    If you need to "relay" or Isolate batteries to prevent discharge find the problem and correct it before it bites you in the a$$.

  11. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,617

    say what you will, I go camping in some pretty remote places and am happy to have 1 battery that I can't drain over night. I can play my radio, use lights, forget to turn off he ignition do any or all of those and more. how about having
    a sticky fuel pump relay. In the morning if I have a dead battery I also have a fully charged one right next to it.
  12. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    For camping sure use an isolator but we are plowing not camping..
    For plowing you want all the amps you can get..no isolaror

    I have tried many different setups im my plow trucks. Two batteries with 1000cca in parallel. With a big alternator is the way to go.
    No switches,no relays,no isolators .
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    And that would be considered an "RV" application...and exactly what a "relay" (isolator) would be used for, and that is a different application. It serves no purpose as far as getting the best current capacity out of a running/charging truck in order to power a plow and accessory lights, which is what the original question pertained to.

    Like I said, theirs nothing wrong with your relay set up plowmeiser as your using it in an RV type application, and I'm not trying to bash you here, I just wanted it to be clear that we're talking about two different applications here. RV applications work best one way, and a plow application works best another way.
  14. Ogrebonz

    Ogrebonz Junior Member
    Messages: 17

    I'm running an isolator in my truck with a 100 amp alternator with no problems after two seasons. Though like the post said earlier, you get what you pay for. The isolator I used is marine rated for 130 amps and continuous use, not a JC WHitney cheapie.
    I considered using a relay between the batteries instead, and I even bought one with a 40 amp continuous, 300 amp surge rating. I use two Interstate batteries rated at 1000CCA each, and I was worried about overloading the relay during starting etc. It probably would have been alright, but the separated aspect of an isolator made me happier.
    Incidentally when the pump relay died on my Western plow I replaced it with that relay. Overkill I'm sure, but it works.
    On the same subject, I know Ford used an alternator on the early 6.9L Diesels (maybe others too I don't know) that had two outputs of over 135 amps each. Has anyone ever considered using one of these alternators?
    No disrespect to the experienced members of the site, just my two cents and your mileage may vary.
  15. Ogrebonz

    Ogrebonz Junior Member
    Messages: 17

    I just remembered an article in the latest Off Road magazine about dual batteries. They are using a small battery isolated out to start the truck with a large one to power everything else. I thought it was an interesting aproach to an old problem.
    Also mentioned in the article is the latest and greatest Isolator, possibly the one mentioned earlier. It's from Perfect Switch and their website is www.perfectswitch.com.
    The article is in the March 2008 issue of Off Road, but it doesn't seem to be on their website yet.
  16. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Thats fine but are they plowing with these off road rigs??
    There is no need for an isolator in a plow truck.
    If you use an isolator you have not increased your capacity.
    You are defeating the purpose of the second battery in this application.

    Do a search this topic has been discussed...

    A friends NEW gmc with plow prep came with two batteries (gasser)
    and guess what NO isolator......
    Last edited: Jan 12, 2008
  17. Ogrebonz

    Ogrebonz Junior Member
    Messages: 17

    LOL, I doubt they plow much out in So-Cal with those trucks, I just found the method interesting.
    With respect I have to disagree with the idea that an isolator is not a good idea. With the second battery isolated and used only for the plow you've got 1000 amps available for use without affecting the rest of the truck's electricals. One other thing to consider, though not applicable to my old trucks, is the idea that modern trucks have computers. Lots of computers. Did you know some of the newer trucks have a computer to control the seat?!
    Speaking from recent experience, (lightning in January?) computers don't get along well with power surges. If your plow draws 150amps or more then the alternator ramps up to compensate that's alot of potential surge. Ok, I'm sure nobody has any problems with toasting modules while plowing, but there are cumalative effects.
    I know I'm new here so I'll just agree that I'm doing it wrong, but since my truck is all wired up already I'll see how long it lasts.
  18. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Speaking from experience,

    I have tried an isolator before..
    For plowing It is better not to use one.
    It works fine for maintaining the battery for my camper which is a different kind and size than the one in my truck..
    Or an on board welder'
    Isolators are nothing new nether are electronics in vehicles..

    How would an isolator stop a power surg?

    Why would your alt not (ramp up ) when you needed the extra power? (in any situation)
    and why or how would this damage anything?

    good luck.. happy plowing....
    Last edited: Jan 12, 2008
  19. Ogrebonz

    Ogrebonz Junior Member
    Messages: 17

    Let's just agree to disagree. I've had my truck set-up with properly with an isolator for two years now, and have done the same for others in the past. Like I said earlier, I'll keep it that way and see if it breaks.
    BTW, thanks for the warm welcome to a new member just posting his ideas...
  20. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    "Let's just agree to disagree." ????
    fact, an isolator is not a good thing to use in a plow setup.
    It can actually be detrimental.
    So you set up a couple of trucks this way so,, you did not do them any favors..
    I've been setting up trucks with 2 batteries for over 25 years......
    You can disagree all you want...

    What do you want?
    A toasted muffin with jam?
    Your first post you just jumped in, so I treated you just like anyone else.

    Just trying to help you out.
    Do a search on this subject if you do not believe me.

    I know it must be hard to move a couple of wires to achieve the desired results of having two batteries for plowing.

    It is a big (surge) draw on your alt when the isolator switches to the AUX battery to charge it.....
    Discharging & charging like what happens when an isolator is used for plowing hard on any battery.

    Your plow can draw over 200amps.
    Two batteries working together is better than 1...

    ........never mind your not going to listen to us anyway...
    Do a search, you are the minority, your method is not the best one for plowing.


    Happy plowing.....
    Last edited: Jan 13, 2008