24V 4.5A PSU fell in my lap. Using it as mains power and NiMH Charger? - diyAudio
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Old 1st June 2012, 06:04 PM   #1
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Default 24V 4.5A PSU fell in my lap. Using it as mains power and NiMH Charger?

As the title says, I came into a nice 24V 4.5A PSU that is small and compact that fits perfectly in my project box.

I'm basically building a knockoff of those 895 Euro boxes. I'm using this Amp. My question is, could I make the internal PSU charge the NiMH batteries if it's not in use? I assume I'd need some sort of unit to detect when the NiMH is full. My battery is 24V 50Ah!!! Yes.. 50. I had it built locally for about $80. It's 20 2500Mah AAs in a 10x10 stack.

I'm thinking a 3-Way switch so I can't power the Amp with BOTH of the Power Supplies (Batteries, and PSU), so I should be okay there.

If my calculations are anywhere near correct.. I should be able to run this thing on batteries all day.

Please point out any flaws if you see any. I've scoured over the Boominator thread.. but after a few dozen pages (and super outdated), it gets frustrating.

Thanks again for everything.
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Old 1st June 2012, 06:42 PM   #2
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Donnow anything about anything, but does 20x 2500mAh actually make 50Ah?
Unless one cell is actually 24V itself? Are there such cells availabe? Where?
Aren't they usually 1.2V/pc?
Which makes a 20 cell unit 24v and only 2.5Ah...???

For the charger, a constant voltage - constant current should do the trick just fine...
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Old 1st June 2012, 06:46 PM   #3
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Originally Posted by palstanturhin View Post
Donnow anything about anything, but does 20x 2500mAh actually make 50Ah?
Unless one cell is actually 24V itself? Are there such cells availabe? Where?
Aren't they usually 1.2V/pc?
Which makes a 20 cell unit 24v and only 2.5Ah...???

For the charger, a constant voltage - constant current should do the trick just fine...
Well, 20x 2500 = 50,000 maH.. That's 50Ah right?

Either way, this thing will last a crazy long time.

Yeah.. I was hoping someone would be able to show me a cool switch, or intermediate gadget that will monitor and shut off my PSU when it sees the batteries are charged.
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Old 1st June 2012, 07:09 PM   #4
jitter is offline jitter  Netherlands
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Putting battery cells in series increases the voltage but not the capacity.
20 cells of 1.2 V/2.5 Ah gives you 24 V/2.5 Ah.

If you find that hard to believe, take apart the battery of a cordless drill. In (e.g.) a 9.6 V/2.0 Ah type you will find 8 cells of 1.2 V/2.0 Ah each.
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Old 1st June 2012, 07:21 PM   #5
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Let's assume you have all the 400pcs of 1.2V cells to make the 24V 50Ah battery pack.
In that case if your PSU is current limited (it is allready constant voltage) You do not need anything else. You allready have it all to charge your pack safely (in 1/10C ie. 16hours)...
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Old 1st June 2012, 07:35 PM   #6
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Originally Posted by jitter View Post
Putting battery cells in series increases the voltage but not the capacity.
20 cells of 1.2 V/2.5 Ah gives you 24 V/2.5 Ah.

If you find that hard to believe, take apart the battery of a cordless drill. In (e.g.) a 9.6 V/2.0 Ah type you will find 8 cells of 1.2 V/2.0 Ah each.

Oh no.. I think I just wasted $80....
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Old 1st June 2012, 07:38 PM   #7
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Originally Posted by palstanturhin View Post
Let's assume you have all the 400pcs of 1.2V cells to make the 24V 50Ah battery pack.
In that case if your PSU is current limited (it is allready constant voltage) You do not need anything else. You allready have it all to charge your pack safely (in 1/10C ie. 16hours)...
Just 20pcs. I obviously don't know what I'm doing.. I'm such a DIYer guy though. I can't believe I paid $80 for the battery.. I thought I had it all figured out.

So, with my battery.. any idea how long it will power the amp I have?
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Old 1st June 2012, 07:41 PM   #8
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Quote:
Originally Posted by jitter View Post
Putting battery cells in series increases the voltage but not the capacity.
20 cells of 1.2 V/2.5 Ah gives you 24 V/2.5 Ah.

If you find that hard to believe, take apart the battery of a cordless drill. In (e.g.) a 9.6 V/2.0 Ah type you will find 8 cells of 1.2 V/2.0 Ah each.
Ugh.. sooo pissed.. 1xAA at 1.2V=2500mAH, but 2xAA at 2.4V=/=5000mAH?
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Old 1st June 2012, 08:25 PM   #9
jitter is offline jitter  Netherlands
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Indeed. And now you know why fully electrically powered cars are still a rare sight anno 2012.

But with the efficiency of class D you might get more running time out of those 2.5 Ah batteries than you might think. Since you have them anyway, why not give it a try?
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Old 1st June 2012, 09:04 PM   #10
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Indeed. And now you know why fully electrically powered cars are still a rare sight anno 2012.

But with the efficiency of class D you might get more running time out of those 2.5 Ah batteries than you might think. Since you have them anyway, why not give it a try?

Oh I will.. I'm just super bummed... I ahve no idea how much Wattage that amp pulls, but at 100W, my calculator only says 25 minutes.. ;( ;(
I could've spent like $25 on a small Lead Acid or something.. I thought I was a genius. I work with a lot of engineers and RC hobbyists.. I was bragging all over.. no one said a word.. I thought I was golden.
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