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Old 02-23-16, 09:29 AM
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Okay. So my Mom has a power lift chair we bought her a few months back and she loves it. Or at least until a power outage the other night left her "stuck" in it. Unit actually has on-board battery back up. If I remember right, the back up power is via a couple of 9v batteries. Not a lot of operating time, but for an emergency get-out-of-chair cycle should be sufficient. My brother is going to check it tonight. What I had in mind, though was to just get a small UPS and connect it and be done with worrying about on-board batteries. Found a low-price APC unit on Amazon and almost ordered it until seeing a Q&A item on the page that concerned whether this unit would provide enough, and right type, of power. Several answers indicated "no", owing to square wave vs. sine wave power running an electric motor and to the amount of power required.

Here's the UPS:

http://www.amazon.com/gp/product/B00...=1&s=pc&sr=1-1

So, my questions. First off, the lift motor is DC AFAIK, operated from a transformer/inverter, so would the wave issue still apply? Second, also because the DC motor, again AFAIK, doesn't draw a huge load, would this be an issue? Unfortunately, I don't have the specs on the motor itself, so unless someone is familiar with them this will be some guess work. The UPS unit says 75w @ 125VAC. As I said, the on-board reserve power I believe is a couple of 9v's. Might be able to get some specs when my brother checks it out tonight.

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Old 02-23-16, 09:38 AM
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Additional info.

Did some surfing and found a similar chair specs. For that one motor is 24V 2.2a and does in fact use two 9v batteries for emergency power. Says good for one "cycle" and also replace yearly. I think we tested her chair when it arrived so possibly killed the batteries right off, duh. Would still prefer to have an UPS for backup power.
 
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Old 02-23-16, 09:43 AM
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If there is room in the chair to conceal the batteries why not use three 6 volt lantern batteries.
 
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Old 02-23-16, 11:01 AM
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Batteries are in the transformer/inverter housing. Like this or very similar:

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Problem with using the on-board batteries, of course, is there's no way to periodically check for operation even when you put new batteries in since they only last one "cycle". Danged if you do, danged if you don't.
 
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Old 02-23-16, 01:42 PM
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If motor is DC, then modified sinewave from UPS inverter will work fine for the most part. Control circuit needs to be looked at first to be sure, but chances are AC to DC power supply is used before anything and all circuit is powered with DC. Using 2 9V batteries for back-up power makes me think it is more likely to be the case.

Get a larger size UPS with ability to turn off alarms. (APC does have models with button in front to turn off alarms.) That way life can be used for extended period without electricity and not getting annoying alarms during power outage.
Beeping UPS can be very annoying.

It would been nice if they just used SLA battery for back-up power instead.
 
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Old 02-23-16, 02:55 PM
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Can you post the specs of the chair (amp draw, etc) and how does it get power normally? Does it just plug in?
 
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Old 02-23-16, 05:54 PM
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Some of those chairs have the option for using a chargeable battery backup that is designed to run the chair for longer periods than the 9v batteries.
 
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Old 02-23-16, 07:29 PM
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Plugs into wall. Cord runs to a small box that contains the 9v backup batteries and the inverter.

My brother replaced batteries and gave it a split second trial with cord out to verify unit would be powered. Let him know about the one-cycle lifespan of batteries. User manual tucked away in one of Mom's drawers, so I'll dig it out for specs my next visit.

As suggested, I think I'm inclined to just get a bigger, regular type UPS to ensure will work when needed, which of course once I take the precautions will be "never".
 
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Old 02-23-16, 08:15 PM
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Since the unit doesn't charge the 9 volt batteries why not just use three 6 volt lantern batteries. Test them every few months. Seems a lot simpler. They'd probably last for years.
 
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Old 02-24-16, 04:38 AM
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Well, that would involve attaching wires to the unit and having the batteries sitting loose. Do-able, but I think a small UPS would solve all issues.

Would have been nice if the unit had a built in rechargeable battery; can't imagine it would have increased the overall price by that much.
 
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Old 02-24-16, 04:21 PM
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Would have been nice if the unit had a built in rechargeable battery
Your mom's unit may be different, but the few units I have been around were all battery powered. The 120 volts supplied by the power cord only powered the charger. Power outage? No problem!
 
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Old 02-24-16, 04:46 PM
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Have you checked with the mfg. to see if they offer a emergency package?
 
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Old 02-24-16, 06:07 PM
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I would think a UPS would work just fine. 9V batteries are not a lot of power.
 
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Old 02-24-16, 11:03 PM
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What I would do if it were mine:

Buy a pair of 7 ah 12 volt gel-cells and wire them in series for 24 volts. Buy a small constant voltage power supply to keep the batteries on a constant charge. Build a nice wooden box to contain the batteries and power supply. Wire the chair to the batteries and the power supply to the 120 volt receptacle with a common plug.

The batteries will power the chair for many cycles before they deplete their charge. Depending on individual circumstances the batteries may last as long as ten years before requiring replacement. Batteries and power supply shouldn't cost more than about $60-$80.
 
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Old 02-25-16, 04:15 AM
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Well, I can get a suitable UPS delivered to my door for under $60, I think, so not sure I want to spend a lot of time on a DIY for the issue.
 

Last edited by the_tow_guy; 02-25-16 at 04:54 AM.
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