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shdesigns
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join:2000-12-01
Stone Mountain, GA
(Software) pfSense
ARRIS SB6121

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shdesigns to Subaru

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Re: battery backup lights

I have one I used:

»shdesigns.org/gcellchg.html

I set it to 13.4V. Will charge fast for the the first 75% then ramps down to 0.

It is what is called a "float charger".

Subaru
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join:2001-05-31
Greenwich, CT

Subaru

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That design looks good and the LED is a nice touch so after I get my battery (might use one I have already) I just find what the charge settings are and just set it to that?

shdesigns
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Stone Mountain, GA

shdesigns

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Yes, see what the OEM says for float charge voltage.

Subaru
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join:2001-05-31
Greenwich, CT

Subaru

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I will have a check, I hope it's listed on the battery, btw nice use of off the shelf parts, I have everything listed but the heatsink and the N22222A

My project box may be a little small but I have at least 3 sizes laying around

shdesigns
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Stone Mountain, GA
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ARRIS SB6121

shdesigns

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Nearly any general purpose NPN transistor will do.

Will need a heat sink. I used a box about the size of a biz card and 1" tall. I replaced the cover with an aluminum plate that doubled as a heat sink.

Works best with about 16V in, higher is just wasted as heat. I use it with a solar panel to keep my riding mower batt charged.

Subaru
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join:2001-05-31
Greenwich, CT

Subaru

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did you take any measurements of the heatsink? I don't know if I have any spare transformers but say it had a 15-17 Vout voltage.. trying to get an idea if that's too hot to run in a case without a aluminum plate but with a heatsink on it..

if it's really bad I could add a small 40 mm fan to the case

SmokChsr
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Saint Augustine, FL

SmokChsr to shdesigns

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said by shdesigns:

I set it to 13.4V. Will charge fast for the the first 75% then ramps down to 0.

Nice little design, The one thing I think I would add is an isolation diode so that the charging circuit didn't become an additional load upon failure. (especially if you need the 1K for the LM317) Of course you would have to compensate for the diode drop with the regulation setting.

shdesigns
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Stone Mountain, GA

shdesigns

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The design was parts I had laying around.

Id probably do a switching reg if i was doing one from scratch.