Author Options:

How to get a UPS to turn on without being connected to AC? Answered

I want to use a UPS and a car/deep cycle battery to get AC power when away from outlets or when the power is off. ie what I want is to be able to have my UPs attached to a car battery and turned off and then when I want to use it turn on the UPS and have AC power.

That would seem easy enough. But it doesn't work. My UPS works fine on the battery if it is connected to AC and then unplugged while turned on. However I can not get it to trun on without being connected to AC. 

What do I do? I have tried two different UPSs.

I am including ictures of my UPSs.

 The white one is APC 280VA model.

The black one is 650VA APC model.

I would prefer to use the black one but I could use the white one.

Thanks for any help.

If you need more info just let me know.



Best Answer 6 years ago

I have a couple models up from the black one, and I found (quite by accident) that if press and hold the power, it will turn on even if it isn't connected to AC. Not sure it will work for you.

The problem I had was that annoying alarm. It will not turn off. I was trying to use it to power my DVR during power outages, but it scared my dog half to death, so I really couldn't use it anyway. :(

I will try holding in the power button but I think I already tried that. I can't hold in the button on the white one because it just has a master power switch.

I'll tell you if this works.

Oh and if you open up the UPS you can just desolder the alarm buzzer so that it doesn't make any sound.

I actually had the same white one... it's battery went bad about 4 years ago. Even my black one I was telling you about died last year... my guess is that since they seem to be the same generation as some that I had and all of mine died already, your batteries are dead. You could try to get replacements for them, but UPS are so cheap, as well as inverters for the car battery that I would just get new equipment.

I thought about desoldering the alarm, but it's pretty dangerous to mess with a UPS aside with changing the battery (even that is dangerous depending on the model), and I'm not good enough with circuitry to attempt it safely.

Anyway, good luck! :)


If nothing else you could get the copper out of the UPS transformers inside.

No problem. I guess that wouldn't be a bad idea... I have a few old ones laying around. ;)

I just saw your comment that you replaced the battery already, so I would guess it probably just will not turn on without power without some major hacking. :(

Well actually I have some good news. Just after I posted my last comment to you I was fiddlling with it and I got it to work. What I have to do is hold in on the power button for about two seconds until I here a beepr and then if I let go real quick it turns on. If I hold any longer it won't turn on.

So it is now working. thanks again for al of your help and I will be selecting yours as a best answer.

Ok. I tried what you suggested and this is what happens.

I start with the battery connected to the UPS and the UPS unplugged from AC power and turned off.

I pressed the button on the front for just a second and there was a spurt of the alarm and I heard some relays clicking inside. But nothing more happened and the UPS didn't turn on.

I now tried holding in on the button. There was a few second long alarm and nothing more happened. This time I didn't hear any relays clicking like before.

I am not sure what to do now.

The UPSs are made to detect a power frailer. So you will have to have them plugged into the wall to start with and have something plugged into the UPS providing a load. Then when you unplug the unit it will stay running for you. Without a load being present it won't trigger the battery to come on.

You would need to have a good understanding of the power circuits in the UPS in order to bypass it and have it turn on at will.

I just skimmed the answers, but if the UPS is not grounded, it shouldn't fire up. That's just a safety issue.

You'll have two options, by pass the safety in the UPS or find away to ground it.

Also advanced UPSs will detect no load and not come on as to not kill the battery. I don't think that is your issue.

Well I have one that I am using as an inverter and it works without being grounded so I guess that doesn't aplly 2 all of them.


Ok let's try this again. Previous post disappeared.

The UPS is designed to work that way. It's a safety issue. If it's not grounded, plugged in, it most likely won't fire up. You'll have to either ground it or hack the safety. Some UPSs have a manual switch so you can fire up the inverter manually, but I haven't seen one.

Also some UPSs require a load to fire up, I don't believe that is your issue. Good Luck.

I have a very cheap ups and it allows turning on/off regardless of the current power input status. If these won't turn on by command then you probably need to find a different solution. As others say, tricking it to turn on would involve fully reverse engineering the internals.

Remember, most ups units have a very limited duty cycle that is designed around the capacity of the battery. They're often not designed to run as an inverter longer than the battery would usually last.

Yeah I am not good enough to seriously mess with the inside of the UPS. I was also planning on using some fans to cool my UPS internalls.

just telling you what I know :)


6 years ago

The battery in it might be no good. I have a number of these also and yes you can get them to turn on by holding the power button a few seconds. However if the battery is really low or just bad they will not turn on. They will cycle and try to but there is no juice for them to convert so they just shut back off. What is more annoying is the models that will not turn on even if connected to the AC because the battery is bad. I have a few of those and I cannot even use them as surge suppressors because they won't work with a bad battery. The models you have in the pictures are older models. The batteries only last 3 years at the max so unless you have changed them they are bad. I have thought of connecting car batteries to these to extend their run time but I have just never done it. Drill a few holes in them for the wires and connect an older car battery and it should work, or at least that is what logic would suggest. Problem is sometimes things are not logical. I currently have an older battery sitting on a desulfater with a charger that has been running for about 3 months now. I am trying to see if the desulfators actually work so you can bring some of these batteries back to life. So far I can't tell.

I have replaced the battery. The one I am trying to use is almost brand new.


6 years ago

Some of those older UPS need a load before they actually come on. Assuming that the battery is good and fully charged, plug a small table lamp (making sure the lamp is switched on first) into the UPS and the UPS is not connected to an external power source. Then press and hold the UPS power switch.

Since you want to use a car battery, why spend all that money on a UPS when you could just by an Inverter for the car battery? Since you already have 1 or 2 UPS's on hand you can pull the charge circuit out of the UPS to charge the batter off AC. Just keep in mind that a car battery does give off harmful fumes and needs to be in a well ventilated area. It would be a good idea to get a case to set the battery in so if the battery leaks you don't get acid all over your desk/floor.

I am not spending money. I have several old UPSs (Like the ones pictured) that I scrounged. I want to use those to avoid buying an inverter.