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Old 06-14-2008, 05:21 PM   #1
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Old UPS to car battery?


I have an old APC 650 and an old car battery, which seems to hold a charge OK but will not start the car reliably. http://www.apcc.com/resource/include...se_sku=BK650MI

The APC has no battery so I was wondering if I could hook the battery up to the APC.

What I can't figure out is if the APC is "standby" or "continuous". I.e., does it run on 12v all the time or does it normally run on A/C then switch to DC when the power goes out?

I have heard part of the problem with APC UPSes is overcharging and I do not want to overcharge the car battery. BTW, this would be in my garage in a marine battery box (on hand already) and battery would be vented to outside.

Could I stick a cheap solar charge controller between the APC UPS and the battery to prevent overcharging?

Or could I put a hook the battery up to a cheap solar panel (also on hand already) and charge controller, then put a diode on the APC so that it can only draw current from the battery, not charge it?

As you can see I have most of the supplies lying around my house, and I am not wanting to really put much money into this ...

BUT, I would like to have a functioning back up power for my Verizon FIOS router and WAP and one of my Linux boxes. I imagine all of these are well well under 650 VA.
I figure a new UPS battery is going to cost at least as much if not more than a charge controller.

Other junk I have lying around include a 400 watt inverter, and various 12 volt power supplies.

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Last edited by pcampbell; 06-14-2008 at 05:23 PM.
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Old 06-14-2008, 11:14 PM   #2
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Old UPS to car battery?


I can see a couple of problems that will need to be addressed here;

1) Battery types; a car battery is a wet cell type, the one built into the UPS is known as SLA (sealed lead-acid), or AGM (absorbed gas mat). While they're both referred to as 12 volt, the charging systems are somewhat different. To get the most out of either type, they like to be 'overcharged' a bit at first, then maintained at a lower voltage. (This is what the charge controller does.) They both like to be taken up to about 15 volts at first, then down to about 13.5 to 13.8 for the SLA. The wet cell likes it a bit lower, if 13.8 is maintained it'll boil it dry in time. Some charge controllers have a switch for different battery types. If it doesn't, it's almost certainly set up for SLA.

2) Most small UPS's use 24VDC for batteries. Usually two 12 volt batteries connected in series. If this is the case, you'd need 2 car batteries.

3) If you use the solar system and a blocking diode, the UPS will be in a 'bad battery' alarm always. (If it has such an alarm.) For a 650VA UPS operating at 24 volts, this diode would need to be 50 amp minimum. You'd need a heat sink of some sort. You'd also lose 0.6 volts across the diode, thus reducing the capacity of the battery. If you don't use any power out of the battery at night, alot of charge controllers aren't smart enough to see it. They will charge a fully charged battery, shortening its life considerably.

4) There are 2 types of wet cell batteries, starting and deep-cycle. A deep-cycle battery can be discharged down to about 20% of its capacity, then recharged many times. A starting battery will only do this maybe 10 or 15 times. I don't think this would be a problem in your case though.

Usually these little UPS's take two 12 volt batteries that are not all that expensive. You can get the factory 'battery packs' for them, but it's much cheaper (and not difficult) to build your own.

Rob

P.S. I like using parts I have on hand and experimenting too, a good part of the advice I give is based on my own successes, or more likely, failures.

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Old 06-15-2008, 06:23 AM   #3
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Old UPS to car battery?


Quote:
Originally Posted by micromind View Post
I can see a couple of problems that will need to be addressed here;

1) Battery types; a car battery is a wet cell type, the one built into the UPS is known as SLA (sealed lead-acid), or AGM (absorbed gas mat). While they're both referred to as 12 volt, the charging systems are somewhat different. To get the most out of either type, they like to be 'overcharged' a bit at first, then maintained at a lower voltage. (This is what the charge controller does.) They both like to be taken up to about 15 volts at first, then down to about 13.5 to 13.8 for the SLA. The wet cell likes it a bit lower, if 13.8 is maintained it'll boil it dry in time. Some charge controllers have a switch for different battery types. If it doesn't, it's almost certainly set up for SLA.

2) Most small UPS's use 24VDC for batteries. Usually two 12 volt batteries connected in series. If this is the case, you'd need 2 car batteries.

3) If you use the solar system and a blocking diode, the UPS will be in a 'bad battery' alarm always. (If it has such an alarm.) For a 650VA UPS operating at 24 volts, this diode would need to be 50 amp minimum. You'd need a heat sink of some sort. You'd also lose 0.6 volts across the diode, thus reducing the capacity of the battery. If you don't use any power out of the battery at night, alot of charge controllers aren't smart enough to see it. They will charge a fully charged battery, shortening its life considerably.

4) There are 2 types of wet cell batteries, starting and deep-cycle. A deep-cycle battery can be discharged down to about 20% of its capacity, then recharged many times. A starting battery will only do this maybe 10 or 15 times. I don't think this would be a problem in your case though.

Usually these little UPS's take two 12 volt batteries that are not all that expensive. You can get the factory 'battery packs' for them, but it's much cheaper (and not difficult) to build your own.

Rob

P.S. I like using parts I have on hand and experimenting too, a good part of the advice I give is based on my own successes, or more likely, failures.
This one is only 12v only and yes has a SLA battery. No alarm on a bad battery though. I thought the point of a charge controller is to NOT let it charge and overcharge a fully charged battery? This is why I have heard many UPS batteries fail is because they overcharge the batteries( and that is their own OEM batteries!).

In looking at a few charge controllers I do not see any yet with switches for battery type. I thought a car battery is typically charged to 13.8 though? Or is it lower...
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Old 06-15-2008, 11:23 AM   #4
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Old UPS to car battery?


In a typical automotive charging system, the alternator will adjust its output voltage from about 13.5 to 14.2 based on temperature. A cold battery needs a higher voltage. What it doesn't do is run the voltage higher (like almost 15), then taper it back. A charge controller does step the voltage.

Part of the reason stepped voltage isn't needed in a car is because in a wet cell, the acid tends to be stronger at the bottom of the battery, and driving mixes it up pretty good. If the battery sits on a shelf, slightly overcharging it will circulate the acid as well. SLA's don't have this problem. The reason SLA's like to be slightly overcharged is it cuts back on sulphation of the plates. Overcharging a wet cell has the same effect, but in a little different way. The key here is to limit the time it's overcharged.

Some charge controllers can detect a fully charged battery, and just go into float charge (13.5-13.8) when they're powered up. Others can't, and will overcharge then float charge every time they're powered up.

Rob
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Old 01-20-2009, 11:22 AM   #5
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Old UPS to car battery?


OK let me try this again. Slightly different situationfrom above. Forget solar panel and forget car battery.

I'm thinking about hooking up a battery of the same TYPE (SLA) to an old APC UPS 650.

What I want to accompish is :
1) Have a working UPS for my computer - have this right now.
2) A power supply for my UHF radio that will work when there is no AC power.

What I am not sure about is how the UPS is designed to recharge the battery. If it charges based on voltage, and I use the same type of battery, I would think i'll be ok. However if it is only designed to recharge a battery of a certain AH capacity, then I could run into problems(???). Any thoughts?

This is an old UPS so I do not have any battery status info available to me on my computer.

Last edited by pcampbell; 01-20-2009 at 11:44 AM.
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Old 01-20-2009, 03:16 PM   #6
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Old UPS to car battery?


I can tell you for a fact the UPS will run on the car battery. I have done it to extend the run time of an APC UPS to use on a float during a parade. I don't know about the charging as I have never applied line voltage to the unit when battery was connected. I simply recharged the battery with my marine charger. I assumed the APC charge rate would be too low to recharge the marine battery.

Last edited by joed; 01-20-2009 at 06:11 PM.
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Old 01-20-2009, 05:53 PM   #7
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Old UPS to car battery?


In addition to the concerns everyone else has raised:

Those small UPSs are designed to only run as long as the small battery they came with would allow them to run. In other words they are often only rated for a 5 minute duty cycle at 100% load. If you put them on a battery that allows them to run 45 minutes at 100% load, the solder on the PCB will melt and things will burn up.

The only safe way to do it is to ensure the load is well below what the "rating" is. In other words, they are often rated up to 2x what they can actually do continuous, because of the guaranteed short duty cycle.

Small UPS do not run the inverter until the power goes off. They are not "online".
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Old 01-20-2009, 06:24 PM   #8
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Old UPS to car battery?


A 12 volt car battery has six units or cells each delivering two volts. Often when the battery no longer starts a car, one or more of the cells holds very little charge. After "normal charging" and then application of a decent load, when the weakest cell fails, the voltage drops quite quickly to 10 volts, when the next cell fails, the voltage drops to 8 volts, etc. A typical UPS on battery power will cut of completely at 8 volts if not 10. (Cutoff expected around 18 or 20 volts for a double battery 24 volt system.)

The result is only five minutes or so run time after AC power goes off. Whereas a good car battery might run your equipment for one to two hours compared with the regular UPS battery lasting for 20 minutes.

If the battery seems to not hold a charge, try rocking/tilting it very slowly and gently several times to mix up the acid inside.
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Old 01-20-2009, 06:34 PM   #9
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Old UPS to car battery?


I guess no one pointed out directly that car batteries are not designed for deep cycling. If you take a car battery down under 50% charge or so you are damaging it. It's designed with thin plates with a lot of surface area so it can provide a surge of current, not a long deep discharge.

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