Reconfiguring a C35 Charge Controller

Sun Dog
Sun Dog Solar Expert Posts: 115 ✭✭
in Off Grid Solar & Battery Systems #1
Has anyone been in a Xantrex C series charge controller (C35/40/60)? I'm curious what they use for an absorb timer.

Their absorb cycle is 60 minutes long but I would like more. Making it adjustable would be great but I would also be satisfied if it could be increased to something like 3 or 4 hours.
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  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    #2
    Re: Reconfiguring a C35 Charge Controller

    It's not adjustable. I have an external micro-controller that looks at the status LED flashes to monitor the charger status. When it's at 5 flashes steady (absorb) the uC starts a software timer that resets the C40 by removing the C40 controller power just before the current absorb cycle hour is over. When this happens it goes almost directly from bulk to absorb if the battery is close to being full charged. Using this method I can set the absorb cycle to as long as I like.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #3
    Re: Reconfiguring a C35 Charge Controller

    That is an impressive work-around, never would have even crossed my mind. Where might someone buy such a setup :roll:
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #4
    Re: Reconfiguring a C35 Charge Controller

    My C12 is also limited to one hour absorb. A temporary workaround might be to just set the absorb and float voltages to the same value. Since I'll never get more than 4 hours of good insolation, and my system is a bit small, I'll probably never have the luxury of a good long float anyway.
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #5
    Re: Reconfiguring a C35 Charge Controller

    Thanks PNj. I was just reading through the manual and it looks like float can be set as high as 14.5V. That should be high enough for most batteries and if not, there is that resistor that can be cut that moves the float range from 12.5-14.5 up to 14.5-16.5 (changes the bulk mode range up by 2V too). My only concern would be how much current is getting to the batteries during this extended float. The manual doesn't give a value, just shows that it is reduced. If you do this, I would be interested to hear what the output current from your C12 is during the high voltage float.
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  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    #6
    Re: Reconfiguring a C35 Charge Controller
    Arctic Donkey wrote: »
    That is an impressive work-around, never would have even crossed my mind. Where might someone buy such a setup :roll:

    It's something that's fairly easy to make as a standalone function for a embedded systems guy with a small 8 bit controller but
    my absorp timer is part of a much larger Battery Management System that's been a testbed for some ideas of mine for a off-grid retirement home system.
    http://flic.kr/p/dQXZCd
    http://flic.kr/p/cAMQv3
    http://flic.kr/p/cAMQb5
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  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    #7
    Re: Reconfiguring a C35 Charge Controller

    Amazing what you can do...................when you know what you are doing. Thanks for sharing.
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