Ideally, I'd like to have a UPS for my PJ as the power goes out at my house a little too often. But as a cheap alternative, would there be a way to set up a circuit with a few regular AA, C, or D batteries (or even better, the little button ones) so that if the power failed, the batteries would keep the fans going for at least 5 mins or so? Even if it really drained the batteries fast, it would probably be very rare they'd ever be used. I don't know if it would be overly complex to set it so the batteries kicked in when the power goes out, though.

On a related note, I know the lamps have to cool a bit before turning back on once shut down. If the power goes out for a second or 2 and then comes right back on, will the lamp try to turn on and, if so, will this damage it? Or does the balast somehow cut off power to the lamp until such time as it's safe to restrike?

It should be fairly simple to do this from an electronics point of view.

All you would need to do is put an AC relay on your input power, and set it up so that on loss of AC power, the AC>DC adaptor is disconnected and the batteries are connected into the circuit.

You would need to use some fairly hefty batteries, and you would need enough of them to make 12V.

D cells would work, C cells should work, AAs are a bit underpowered, AAAs are underpowered and button cells are a joke.

If you get regular outages, you might want to consider using rechargables, and these tend to hold more power also.

The following circuit should do the job.

That's hugely more complicated than needed. You could get a 12V sealed lead/acid battery for alarm systems for like $25. Just put it in parallel with the power leading directly to your fans. When voltage is high, the battery is charging and the fans are going, when voltage is low the battery will kick in its juice, and when input voltage is gone, the battery will work.

That is true, but if you did that the fans would keep going when you switched the projector off, and they would keep going until they totally drained the battery, which would cause it to wear out very quickly (Lead-acids hate deep discharges).

You need the relay to switch the fans off when the projector is switched off (the input AC is pre-switch so the relay will stay connected to the AC adaptor not the battery when the projector is switched off)

or you just open the lid on the projector if the power goes out and dont worry about any of this

Yeah, but if I'm gonna spend $25, might as well spend a little more and get a cheap UPS. The Energizer I use with my comp was only like $20 after $20 rebate.



If that would be sufficient, I probably wouldn't worry about a backup. How much time do you think I'd have to get the top off before the LCD started to melt? Also have to remember I'd be fumbling for it in the dark

Ah, but if you buy a cheap UPS, it will be powering the whole thing, and then the lamp will die at the same time as the fans, and with a 400W constant load on a cheap UPS it isnt going to last very long.