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KATOOM's avatar
KATOOM
Explorer
Aug 09, 2013

Adding an isolator for gen starting battery?

I apologize ahead for redundant questions but cant find a decent search result to answer my question.

I'm redoing my battery setup in my TH. The two marine/deep cell batteries aren't cutting it for more than a couple days of boondocking. Actually, they arent terrible but starting the gen is not possible after that time. I'm sure size of TH and amount of people is playing a part in how fast the batteries drain, but no matter, I'm reconfiguring the house battery type and quantity to see if I can make it so at least three or four days is easy without starting the gen. In saying that, because the gen starts off house batteries since there's no specific gen battery, I want to designate a separate gen starting battery and isolate it from the other house deep cell batteries so it also gets charged when plugged in to shore power or when the gen is running.

Does anyone have any experience with an isolator setup like this (and isolator type), and is there any feedback you can offer? That being negative and positive. Thank you everyone as I know there's lots of members who are pro's at battery tech. :B

8 Replies

  • KATOOM's avatar
    KATOOM
    Explorer
    Aug 10, 2013
    gandude wrote:
    Cant you just dedicate a battery to the gen start solenoid side and leave the house bank on the power converter. Then have a 2 amp charger/maintainer running off the 120v when gen is running to charge the start battery?


    This may be my best and simplest option.
  • gandude's avatar
    gandude
    Explorer
    Aug 09, 2013
    Cant you just dedicate a battery to the gen start solenoid side and leave the house bank on the power converter. Then have a 2 amp charger/maintainer running off the 120v when gen is running to charge the start battery?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Aug 09, 2013
    Below is my excuse to spend the extra thirty dollars for an automatic switch:


    FORGET
    /f?r?get/
    Verb

    Fail to remember.
    Inadvertently neglect to attend to, do, or mention something: "she forgot to lock her door"; "I'm sorry, I just forgot".

    Synonyms
    omit - neglect - unlearn - leave

    OR...........

    "Honey can you go outside for me, open the generator lid, and turn the generator switch to off?"

    "Are you out of your mind? You can't even see the tree it's raining so hard".
  • wolfe10's avatar
    wolfe10
    Explorer
    Aug 09, 2013
    I would get an inexpensive manual marine ON/OFF switch. OFF, battery bank isolated. ON, all batteries connected for either charging or discharging.

    Next step up would be 1-Both-2-Off manual marine ON/OFF switch. That way you could select either/both batteries for charging or discharging.

    For your purposes, I don't see the advantage to the expense and complexity of an electric switch/solenoid to do this.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Aug 09, 2013
    .7 volt is with a meter. A new Sure-Power 70-2 or 160-3 at 50% of design I rating would typically show 1.2 - 1.4 volts drop across the junction. Going the KKK 1811-AA route was not much better. The Skottky device isolators had a ridiculously high percentage failure rate. Ralph Scheidler was a PhD in thermodynamics. He designed the heat sink radiation area meticulously for each device. Those fins are NOT THERE to dissipate a .7 volt junction drop.

    Silicon device battery isolators went the way of rotary dial telephones thank god.
  • RoyB's avatar
    RoyB
    Explorer II
    Aug 09, 2013
    In todays world of charging deep cycle batteries you cannot use the old days DIODE BASED battery ISOLATORS. These devices uses high current DIODES which will drop your DC VOLTAGE by .7VDC going thru them. In the older days this was not a problem but todays DEEP CYCLE batteries require 14.4VDC to properly re-charge the batteries in a short three hour time period. If you subtract 14.4VDC-,7VDC voltage drop then you only get 13.7VDC to charge your deep cycle batteries, This will take around 12-13 hours to re-charge your deep cycle battery to be able to use it immediate again.

    This is why you must install SMART RELAYS verses DIODE BASED ISOLATORs like shown above which will parallel batteries to your normal start battery when charging is needed. This method will keep your down-leg batteries re-charged and never discharge your start battery setup.

    Read up on BLUE SEA SI-ACR charging circuits at their web site - good info there to give you some ideas on what you might need to install.. Same goes for the SURE POWER INDUSTRIES website. Lots of good application info there as well.

    Roy Ken
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Aug 09, 2013
    KAT,

    Some newer versions of te same as mine also crank the APU from the house bank. Some owners in your same situation have added a start battery for the APU - the cheapest, but not smallest you can buy. (Garden tractor batteries are often more expensive than little car batteries.) They usually add a thing called a combiner that will cross the two batteries together only when there is charging voltage available. These devices are vary available at marine suppliers. With that installed the APU start gets charged any time the house bank is getting charged.

    My coach came with a battery dedicated to the APU and the APU charges it when it runs, but there is no cross feed and I like it that way.

    Matt

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