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  1. #1

    Default AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Hey guys.

    Using an Optima spiral cell "dual purpose" battery (Optima D31M) with my `82 Johnson 90.

    While on the water yesterday I noticed that with the engine at 4-5Krpms the charge voltage from the j90 regulator was about 16v or so, which is quite a bit higher than the AGMs are designed to tolerate.

    Rather than smoking my new AGM battery with charge voltage that's too high, I'm thinking of adding an inline boost buck converter to regulate the charge voltage down to a safer 14.1V

    Heres the device im considering:
    https://www.ebay.com/itm/DC-DC-Conve...l/124266576885

    I would basically wire this inline with the factory regulator output before it feeds back into the battery & adjust the output volts/amps to levels the AGM can tolerate.. Thinking this inexpensive mod would eliminate over charging & help keep my AGM healthy.

    Has anyone tried something like this, or can anyone suggest a better alternative?

    Thanks!

  2. #2

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Install the correct wet cell battery for your motor.

  3. #3
    Join Date
    May 2015
    Posts
    2,361

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    CDI electronics makes a regulated rectifier for your motor.

  4. #4

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by Rwbutler View Post
    Install the correct wet cell battery for your motor.
    Ignoring this response.

    ----

    Though this may not be the OEM supported solution, I see no reason why a boost buck regulator cant be safely installed to bring the J90's charge voltage down to something the AGM can handle.

    Anyone else have any advice or suggestions that do not involve replacing the battery outright?

  5. #5

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by flyingscott View Post
    CDI electronics makes a regulated rectifier for your motor.
    Suspecting this is intended as factory replacement & for use with a flooded battery... Also, no option to buy on the cdi website... \_(ツ)_/

    Spec/install sheet says 8v output at 1000rpm & to expect 15.5v, at WOT.. Also suggests using a Flooded cell battery.. So, i'd still be weary using this with my AGM.

    https://www.cdielectronics.com/product/193-3408/
    https://www.cdielectronics.com/wp-ad...S-193-3408.pdf


    I'm opposed to using a flooded battery, because I will inevitably fail to have distilled water when I need it & will waste time & money in the process of attempting & failing to properly maintain a 'maintenance required' battery.

    The nice thing about a boost/buck converter is the output voltage will never change, no matter what the input voltage is.. seems like a much better solution than a non-boost/buck regulator with a constantly changing output voltage.

    Wondering if there are any genuine EEs out there able to intelligently comment on this issue?

    Thanks guys!

  6. #6

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    If we were EE's,we wouldn't be working on outboards.im sorry,are you anEE?

  7. #7

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by Rwbutler View Post
    If we were EE's,we wouldn't be working on outboards.im sorry,are you anEE?
    Im not an EE, hence the questions.

    I do, however, know one of these when I see them.

    Click image for larger version. 

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  8. #8

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Who do you know that adds to a battery? If you over cook it yes. But standard flooded battery can with stand over charger of old type stator an or lighting coils. Optima battery AGM's can't.
    And are not recommended to be used
    .

  9. #9

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by Mikey N.C. View Post
    Who do you know that adds to a battery? If you over cook it yes. But standard flooded battery can with stand over charger of old type stator an or lighting coils. Optima battery AGM's can't.
    And are not recommended to be used
    .

    Perhaps AGM isnt the book recommended solution circa 1982. Looking to apply 21st century solutions (e.g. boost buck regulation) to this motor to allow me to use a modern battery. Not everything needs to be done by the book. If no one here has attempted what I'm suggesting, thats ok. I'll try it anyway and let you guys know how it turns out.

    Thanks!

  10. #10

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by HarborRatt View Post
    Im not an EE, hence the questions.

    I do, however, know one of these when I see them.

    Click image for larger version. 

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    one of those shoudnt be hooked to motor battery.

  11. #11

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Have you given any thought that your alternator system is not working properly?

  12. #12

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by Rwbutler View Post
    Have you given any thought that your alternator system is not working properly?
    Indeed I have, which is why I checked the charge voltage last time I splashed the boat. With my VHF radio on & a usb charger active, system voltage at 5500rpm was 16.1V.

    Is there some other value I should be seeing at WOT that would suggest my charging system is somehow faulty?

    I think the charging system works as intended & it's just not ideal for an AGM, which is why the manuals suggest a flooded battery.

    Flooded batteries can perhaps "tolerate" over volting by boiling off the electrolyte solution. However, I hardly consider that proper "tolerance" as ignoring low electrolyte levels caused by over volting will ruin a flooded battery just as quickly as over volting an AGM \_(ツ)_/

    Ended up buying this LTC3780 boost/buck regulator which should let me hold the charge voltage at 14.2V regardless of the input voltage from the oem regulator. Will report back once I'm able to install & test. If it works, I'll put a big heat sink on it, encase it in epoxy & run it.

    https://www.ebay.com/itm/LTC3780-130...r/152947310464

    Still interested to hear if others have tried this, or another solution that lets them safely run a "dual purpose" AGM like mine.

    Thanks guys!

  13. #13

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Ya think maybe its overchargin ?

  14. #14
    Join Date
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    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by HarborRatt View Post
    .....Wondering if there are any genuine EEs out there able to intelligently comment on this issue?....
    The link you posted is for a step down converter....i doubt it will work for your intended application without some major modifications..big reason is the stator/rectifier doesn't produce sufficient output voltage, at the lower RPM, to satisfy in the operation conditions of the step down regulator.

  15. #15

    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Quote Originally Posted by makomark View Post
    The link you posted is for a step down converter....i doubt it will work for your intended application without some major modifications..big reason is the stator/rectifier doesn't produce sufficient output voltage, at the lower RPM, to satisfy in the operation conditions of the step down regulator.

    Yeah.. the first link I posted early on in this thread was a step down converter & I didn't end up buying that one..

    This is the one I settled on which should work for my purposes : LTC3780-130W-DC-Synchronous-Buck-Boost-Step-Up-Down-Voltage-Current-Regulator

    https://www.ebay.com/itm/LTC3780-130...r/152947310464

  16. #16
    Join Date
    Sep 2008
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    Maryland - USA
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    Default Re: AGM battery, thinking about adding a Boost/buck converter inline with my J90 charging system

    Much better choice with the up/down type of regulator.

    Only item I'd be leeery about with that one is it appears to be limited to 10 amps...as long as you know about it, and plan for it, you should be ok...

    You may also want to investigate 'conformal coatings' to ensure your mod has a decent service life...

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