UPS as robot power supply

Hey all;

anyone tried using a pc UPS as a robot power supply? I've got an old backUPS pro with a 12v/7aH battery. It's also got a serial port so it can be connected to the atx motherboard i'm using. This way, i can poll it for battery voltage over the serial line. The pc psu will plug right into it, though i expect i'll lose some efficiency with the dc/ac/dc conversion. The motors/oopic sub-controller board might be able to run off of a second (or the same) psu wired onto its +12v/+5v rail. It'll also be able to charge the battery automatically and without having to shut down the mobo when the bot reaches its charging station. Comments?

Also, would it be possible to just swap the ups' 7aH battery with a say 12aH one without any other modifications to the unit?

Thanks for your time, Will

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Yes, I'm currently using a UPS to power all the stuff on a large robot, the efficiency of today's UPS units is really quite good, and actually ends up being lower cost than trying to "roll your own". I find it especially nice since a number of peripheral devices (video gear, laptop) use wall warts and it's easier to just "plug them in" to the UPS instead of spending a ton of time designing 12V to whatever converters.

I'd advise against swapping to a bigger battery, I believe the UPS units are usually designed for a specific amp-hour battery (but I'm not totally sure of this).

Let me know if you'd like a pic of my bot with the UPS.

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Arthur Ross

Hey Arthur, i'm glad someone's tried this before. Some pictures of your bot would be fantastic; just send me an email ( My UPS uses a 7aH battery; what's the capacity of yours and how long does your bot operate on it? does your robot auto-dock to charge? if so, how did you manage this?

Thanks alot for you help, Will

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Be aware that some of the newer UPS's uses a set UP time depending on model. Ie 5 minutes for the smaller model, 15 minutes for the "next size up". 2 reasons, one being that some units are borderline and the heat buildup is not acceptable for a long time, two being a sales/marketing issue. Generally you will find the 2 to 3 year old models excellent and genearlly you can easily use a bigger battery. We do it all the time to get the up time on remote sites. We have customers who require a remote PC to be kept up for 8 hours or more, after a power cut, on a

500VA unit, so we add a stack of batteries. Use a fuseable link for remote batteries as when connecting them up any voltage variation may cause some sparking. Or even better use a resistor, ie 50 ohm, with a switch and connect first then switch over after 30 seconds or so. No sparks on battery side.

Cheers K

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Thanks for the advice K; I'm going to try the UPS with a car battery tomorrow, as it's internal battery does a pitiful job at powering my machine, even with the monitor off and no cpu activity. The PC is an old PII

266mhz, 64mb ram running on a 230w power supply connected to a BackUPS PRO 280. With the monitor off, i got about 5 minutes of battery time, a minute fraction of the time a mobile bot is going to need, and this time isnt even including a monitor, cpu activity or motor draw. The ups battery is a 12v 7ah. Anoyone else tried a car battery(ies) with a ups? this is gonna void the warranty...

Thanks, Will

Reply to
Zann & Ling

Probably be disappointed with a car battery. they are designed for high current short duration output, you would need something designed for long duration output. golf cart, trolling motor, etc.

Reply to
Bob Yates

Hi Will The only thing with car batteries is that tend to fall over and the acid goes where it shouldn't. I have used car batteries on the odd occation where we have been short on the proper battery (like none in stock) and the UPS was need urgently. Works ok but shorter lifespan. Sometimes you can get "free" batteries from the UPS supplier where a battery does not match the others in a string, ie either over/under voltage but apart from that it OK. The 7aH should give 20-30 minutes if in good nick. Parrallel them up, Cheapest option. Should sell for less tha USD10 a piece as they are USD2 out of China. K

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Stationary deep cycle batteries are especially designed for UPS applications and car batteries should not be used because they will not charge properly by the UPS's charger and car batteries are not designed for deep discharges. For optimum battery service life, motive deep cycle batteries should be used in robotics. For more information on deep cycle batteries, please see Section 7 in the Car and Deep Cycle Battery FAQ on

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Kindest regards,


Reply to
Bill Darden

Hi Bill I know car batteries should not be used but in pinch they can work. For home robot/low budget/non-critical applications, a new deep cycle USD300 battery may not meet the budget. Thats all I was trying to say. Last resort etc, don't used them if at all possible ..... :-) Kim

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Don't you have some EMC problems ? Power inverters are not known to be "emission free" !!! Off course if you dont have any analog sensor it doesn't matter ...

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