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burningman's avatar
burningman
Explorer II
May 04, 2014

Home made battery isolator system

I thought I'd put this out there in case anyone else likes the idea;
I never liked the battery isolators I had. They had voltage loss and sometimes just failed. Then I went to a marine type battery switch, but I always had to remember to switch it on or off at the appropriate time.

So... I bought a continuous-duty rated electric solenoid and wired it to connect/disconnect my house and starting batteries. To activate it, I got an oil pressure switch. The one I use was intended for a forklift, they were available in different pressure settings (how much oil pressure it took to trip the switch). I unscrewed my engine's oil pressure sensor and used a tee to screw the original and my new one on.
This way, the batteries only connect when the engine is actually running, not anytime the key is on.

I added a toggle switch just for more control and left the marine switch in place for even more redundant backup, but it really works great.

You can simply tap off the original oil pressure sender if you have an. "Idiot light" instead of an oil pressure gauge, but it switches ground, not "hot" so you'd have to arrange your solenoid to work that way (isolated mount, or go through another relay).

7 Replies

  • RoyB's avatar
    RoyB
    Explorer II
    May 04, 2014
    The SMART SOLENOID do about the same thing except they measure the DC VOLTAGES from the truck charging system and the add-on batteries are only connected when the truck system is charging batteries with the motor running.

    The BLUE SEA SI-ACR smart relay does the trick...

    The SMART SOLENOID idea replaces the DIODE BASED isolators we all used in the past which had 0.7VDC VOLTAGE DROP across the high current diodes. With todays deep cycle battery charging technology there is a hugh different is charging batteries at 14.4VDC verses 13.7VDC after voltage drop occurs using smart mode charging technology. With 14.4VDC you can re-charge a deep cycle battery back to its 90% SOC in around three hours of charge time whereas 13.7VDC will take almost 10-12 hours to do the same 90% SOC charge. The Blue Sea SI-SERIES 120AMP add-a-battery package cost around $100 from AMAZON.

    Roy Ken
  • NRALIFR's avatar
    NRALIFR
    Explorer
    May 04, 2014
    That's pretty much what I did. A continuous-duty solenoid from NAPA, and I'm controlling it with one of the up-fitter switches that were just sitting there doing nothing. They're only active when the engine is running with the key in the ignition (not remote started).

    While I was at it I connected a second up-fitter switch to the appropriate wires under the dash that tell the ECM to go into "Battery Charge Protect" mode, which causes it to monitor the battery voltage and manipulate the engine idle enough to keep the batteries fully charged.

    :):)
  • KD4UPL's avatar
    KD4UPL
    Explorer II
    May 04, 2014
    That will work for sure. It seems like a voltage controlled relay, also called an automatic charge relay, would have been simpler. Blue Sea makes a nice ACR I've used for several different applications.
  • burningman's avatar
    burningman
    Explorer II
    May 04, 2014
    OnaQuest wrote:
    Clever, but hardly unique. The oil pressure switch has been used in the past in many Marine and British alternator/regulator applications.


    Yeah it's true what they say, there's really nothing new under the sun!

    I did the setup last summer and have forgotten where I ordered the solenoid, but I know when I did it I just googled it and mail ordered one for about $30 or so.
  • OnaQuest's avatar
    OnaQuest
    Explorer
    May 04, 2014
    Clever, but hardly unique. The oil pressure switch has been used in the past in many Marine and British alternator/regulator applications.
  • pianotuna's avatar
    pianotuna
    Nomad III
    May 04, 2014
    Hi,

    Well planned and well done. I, too, chose to have manual switches.
  • Horizon170's avatar
    Horizon170
    Explorer
    May 04, 2014
    Can you give a link for the continuous duty solenoid?
    Thanks for the post.

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