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NetWorker
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Re: More info about mUPS

Mon Jun 03, 2019 8:18 pm

Brochure says max battery charging current is 1A ... so it'll take ages to charge that "massive" 18Ah battery when fully discharged even if power adapter used is powerful enough.
Other than that, 18Ah battery should be fine.
Thanks for replying mkx. Actually, I have another question related to the brochure: it says 1A out on PoE. It says nothing about charging the battery. Does it draw the power for charging the battery from that 1A too or if I hook a 24V 2A PSU up to it, I get 700 mA on the PoE and 1A and change on the battery?

My thinking is if it goes down to about 30% and I usually draw the line at 50%, I'd be looking at 12-14 hours recharge times which I can live with.

My main concern with the 18Ah battery is that if it's not well regulated it can draw too high a current during initial charging and melt something inside the mUPS after only 20 cycles or so.
 
mkx
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Re: More info about mUPS

Mon Jun 03, 2019 11:15 pm

I have another question related to the brochure: it says 1A out on PoE. It says nothing about charging the battery.
The brochure has "Specifications" table on the top of second page. Pennultimate row reads "Battery charging current 1 A max" (and ultimate row mentions PoE out max current).
Does it draw the power for charging the battery from that 1A too or if I hook a 24V 2A PSU up to it, I get 700 mA on the PoE and 1A and change on the battery?
The brochure doesn't mention any power in limits (neither barrel-plug nor PoE-in). But let's do some math: for battery charging it'll dedicate max around 15W (13.5V and 1A gives 13.5W and let's add some losses on DC-DC converter). PoE out is limited to 0.7A @24V which is slightly less than 20W (more precisely it's 16.8W). Both combined are less than 35W, which means less than 1.5A @24V. Surprisingly supplied power adapter is rated exactly the same.

So given supplied power adapter and full rated loads on PoE out, your 18Ah battery being flat should fully charge in around 24 hours. Or around 10 hours from 30% to 80% charge.
My main concern with the 18Ah battery is that if it's not well regulated it can draw too high a current during initial charging and melt something inside the mUPS after only 20 cycles or so.
My guess is that any 12V lead-acid battery with capacity of a few Ah can draw much more than 1A when not completely charged if charger blindly applies 14.2V to its terminals (quite often that's voltage used to minimize charging time but it's too high as permanent/idle charging voltage, it causes gassing for most batteries shortening their life time). So I'd expect mUPS to have some current regulation built in or else it'd emit smoke in seconds (and we all know that electronic elements run on smoke ... after they let it out, they stop working).
BR,
Metod
 
pe1chl
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Re: More info about mUPS

Mon Jun 03, 2019 11:41 pm

Such a charger normally operates in constant-current mode below a certain voltage, then clamps at a fixed voltage curresponding to fully-charged battery, where the current will drop.
Hopefully not at 14.2v but more like 13.8v.
Of course, a really good charger has more clever characteristics than that, but it is difficult to do it in such an unmanaged device.
(it would require knowledge of battery temperature, type, capacity, etc. so it would require configuration, sensor, etc. by then it is simpler to deliver the unit with built-in battery)

One should be careful not to use a battery with too high capacity, because the behavior of the battery will change when trying to charge it with so low current relative to a large capacity.
But at 18Ah, so charging at 1/18 of the Ah capacity, that should not yet be a big problem.
 
NetWorker
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Re: More info about mUPS

Mon Jun 03, 2019 11:56 pm

Lol, that makes sense. Thanks again! I'll post back if we decide to give it a shot. Right now we're leaning towards a different setup.

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