Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: battery isolator vs relay

  1. #1
    Maximum Bitrate
    Join Date
    Oct 2001
    Location
    Ontario, Canada
    Posts
    845

    battery isolator vs relay

    I've got a question about using a relay (cheap) vs a battery isolator/diodes (expensive!)

    Before I go any further, I know about the "reason" why you should never use a relay, namely once the relay closes the drained battery will draw 47 billion amps from the charged battery, damaging both batteries and melting wires and causing large fires in the process.

    But instead, what if the relay was attached to close only about 5-10s after the engine was started?

    Then the power will be provided by the alternator instead of draining the primary battery, this should work, no?

    Alternatively, can I just build a battery isolator using a couple of diodes? Hell, even those diodes are much more expensive than a relay. You'd need what, probably 100-120A diodes, or 2x60? At like $10 each you'll need what, 4 of them? Still not a very cheap venture.

    [Edit: I'm on crack, you can get MBR6045's for like $3 each... $12 for diodes + wires + heatsink isn't that expensive. And yeah you can buy them for $40 or so, the place I was looking at was grossly overpriced.]

    I tried searching for topics like this here and didn't find any.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  2. #2
    FLAC
    Join Date
    Aug 1999
    Location
    Washington D.C.
    Posts
    1,542
    Is a battery isolator really all that expensive? I seem to remember seeing a low amp one GI Jo's for about $30 and a high amp one for about $50.

  3. #3
    Newbie
    Join Date
    Sep 2002
    Location
    Manitoba, Canada
    Posts
    36
    Here is a good site that illustrates three different ways of connecting two batteries to one alternator.

    Direct Page Link

    It shows a) Diode Type Isolators - same as the ones you buy b) Solenoid Type Isolators - manually switched isolator and c) Dual batteries without an isolator.

    Piles of good info at this site, here is their Main Page
    ~~~~~~~~~~~~~
    Chkdsk
    Shuttle ST62K, 80Gb, MediaEngine, Irman, Wireless NIC, Win2K, Blah Blah Blah...

  4. #4
    Maximum Bitrate
    Join Date
    Oct 2001
    Location
    Ontario, Canada
    Posts
    845
    The isolators that I saw were like $100 (CDN) sorry, I was looking at http://www.sounddomain.com/shop/list...ors/Regulators

    As I keep searching though, the only decent ones that I see are > $50USD, which in my books constitutes "expensive" for what I want, especially since I could build one for like $8USD (using 2 or 3 45V 60A diodes in parallel for each direction)

    And now that I think about it, maybe I'll just build one.

    I'm trying to figure out other neat ways of doing this... I was thinking maybe using solar cells to augment the power supply. Basically you need about 250mA at 5V (so 1.25W, or 1.8W with switching regulator, or 3W with a linear). So with a 5W solar cell, you should be able to power the computer in STR during the day and generate enough power to charge the battery to recover the loss drained during the night. You can get a 5-watt solar charger for $50USD over here at Canadian Tire (probably cheaper elsewhere). Could be interesting.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  5. #5
    Newbie
    Join Date
    Apr 2003
    Posts
    30
    Lets see where this goes...I am very interested...did you ever think about trying it in a friends junker first...lol

    I am thinking about just saying F-it and running dual alternators...very expensive

    JMM

  6. #6
    Maximum Bitrate
    Join Date
    Oct 2001
    Location
    Ontario, Canada
    Posts
    845
    I don't see how dual alternators would really help anything, unless the problem is you're drawing too much power for the poor alternator to handle.

    The issue here is a dual battery system and how to isolate them.

    I think either method would work, but using diodes (since you can actually make one yourself for ~$20 all-said-and-done) seems like the best solution.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  7. #7
    Newbie
    Join Date
    Apr 2003
    Posts
    30
    well, i have so much crap in my car now, i am worried about the pull on the alternator...so yes, the diode method seems like it may be good in my situation also....hmm, i would like to see how this goes.....got an update?

    JMM

  8. #8
    Maximum Bitrate
    Join Date
    Oct 2001
    Location
    Ontario, Canada
    Posts
    845
    no, in the last 15 minutes nothing has changed.

    Ask me after tuesday (last exam). Then I'll be playing with all my stuff
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  9. #9
    Newbie
    Join Date
    Apr 2003
    Posts
    30
    LOL, no Telek...the 'got an update' part was intended for the person who started this forum...I am not an idiot...lol, that was funny...

    jmm, did you get the post about the Krocera vga screens on ebay...I posted to you in the one we have going, "Mailbox is full, Question for Telek"....

    JMM

  10. #10
    Maximum Bitrate albysure's Avatar
    Join Date
    Dec 2000
    Location
    pittsfield, ma.
    Posts
    685
    well i don't know just how young you guys are , but i've been buying stuff from jc whitney for a real long time. i got my battery isolator from them. bought it around 1980 for a van-never used it. put it in my car in '86. its never let me down yet. sometimes you can get pretty good stuff there for a good price--just dont buy their tools!

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •