Back Up Power system Questions. Answers needed soon as blackout expected!!!!!!

fishquaria · 08/04/2007, 01:24 AM

I am putting together a backup power system. I'm modifying an old ups to hold two 7AH batteries twelve volts, in parellel, to run my main filter during a blackout. What I want to know is how long will I be able to run my main filter, which consumes 33 watts at 230V AC.

More importantly, I have a 75AH battery. Can I connect that to the UPS, will it charge properly... Please tell me as soon as possible as we are expcecting power faliures which could last a long time...

Please also tell me what I'd need to do if I can't hook up the 75AH battery directly... Thanks.

Bandsaw · 08/04/2007, 06:52 AM

Well, since P (power) is equal to Volts X Amps, then at 230V, your 33W pump will draw 0.143A.

Now figuring out what your 7AH battery is going to give you is hard to say. That all depends on the efficiency of your UPS. It takes a considerable current draw from a low voltage DC source to produce a 230VAc output (by straight transformer theory, that is 19:1 step up, so for every 1 amp out at 230Vac, you need 19A input at 12Vac, for a straight transformer). It is not as simple as that as we are taking 12DC in, convert to AC, etc, but I think you the idea.

The best thing to do is check the specs on your UPS. It should tell you there what its input current is at maximum output load. Then work the numbers from that.

With reference to your 75AH battery. Again, you will need to check your specs on your UPS. Is the battery the same type as the one you are replacing (Lead Acid, NiCad, Lithium Ion). Not all batteries are charged the same. If 7AH battery and the 75AH battery are the same type, there should not be a problem. It will charge. If they are not the same type, you run the risk of an exploding battery or the battery giving off dangerous emissions.

Just a word of caution. Dealing with electricity is always a dangerous game at any voltage. Unless you have complete competence in what you are doing, I would recommend getting a UPS designed specifically to connect to an external battery and follow the supplied instructions.

fishquaria · 08/04/2007, 07:06 AM

Jeff, thanks so much for your reply, very comprehensive. The ups runs on sealed lead acid batteries. The ups is quite old, so you can't really see the specs. All I can tell you is its 230V at 50Hz.

Please help me calculate at least a rough estimate of how long my pump will run on the two 7AH batteries connected in parellel. Please also tell me if it is then safe to hook up a car battery considering that the batteries in the UPS are sealed led acid and the car battery is a wet lead acid battery.

I am worried that if I do connect my UPS to the car battery the ups might over heat, is this a possibility?

Please please help me as I'm not home most of the time to attend to the fish in the event of a power faliure and leaving emergency care to the people at home might leave my fish dead anyway... he he... please tell me all you can. I deeply appreciate all you've told me already...

Thanks so much, Jeff...

Bandsaw · 08/04/2007, 07:57 AM

Out of curiosuity, where are you located? I ask because you are saying 50 Hz.

This is only a guess. But a 7Ah battery should get you an hour or so?? If it's an older unit, then it's effenciency may not be that great. Newer UPS/Inverter have an effenency closer to 90% (means only 10% of the input power is used to actually run the UPS).

Like I said, it is really only a guess.

You should not overheat the UPS. It probably has a current limit circuit that would prevent it from overdoing it self. Important thing is to keep the leads to the battery as short as possiable and use as large wire gauge as you can.

fishquaria · 08/04/2007, 09:26 AM

Colombo, Sri Lanka... But since it's 7AH X 2 in parellel, that effectively makes it 14 AH right? So what you're saying is that I can connect a car battery to it without any fear?

Thanks for all the help... if there's anything else you can add please do so... thanks a million.

Bandsaw · 08/05/2007, 08:39 AM

What you can do is if you have access to an Ampmeter, connect the ampmeter to the battery and run your pump (with the UPS unplugged). Measure the current being drawen from the battery. That will tell you how long you can expect the battery to last.

Yes, I beleive the AH rating would be 14 AH when connected in parallel like that.

Just use some caution when trying to charge the big battery. Monitor it. Again, if you have access to an Ampmeter, the Ampmeter will tell you how hard the battery is being charged and if the UPS is stopping the charge when the battery reaches its nominal charge (13.23Vdc).

Good luck with it all. Having a backup sure is nice.

BeanAnimal · 08/05/2007, 09:15 AM

Parallel batteries can pose a great danger. If a single cell shorts internally, the other cells will see the short and supply large amount of current. EACH BATTERY in a parallel circuit must have its OWN fuse. LARGE diodes can be used to prevent one cell from feeding another. Though, you will not be able to charge with the diodes in place.

Cells of different sizes can pose an overall capacity problem in parallel. The larger capacity battery will carry the brunt of the load and discharge though its curve faster than it would otherwise. This is complicated but let me try to explain.

(1) 50Ah and (5) 10Ah batteries = 100Ah
(2) 50Ah batteries

given the same load, the (2) 50Ah cells will last longer than the combination og (6) mixed cells.

Is s generator out of the question? What lenght of power outage do you plan onm preparing for and what is your proposed current draw during the outage? Just 33W? What about heat?

fishquaria · 08/05/2007, 10:06 AM

Luckily the ambient temperature doesn't drop below 26 degrees over here and highs are generally 34 degrees but that's an off day. So tank temp can easily be maintained at 27 degrees celsius with a heater and fans... (The heater is for when the A/C is on)... he he. I am now using a 75AH battery... Waiting to see the results... it's currently charging...

Thanks for all your info and will get back to you.

08/04/2007, 01:24 AM	#1
fishquaria Registered Member Join Date: Jun 2007 Location: Sri Lanka Posts: 170	Back Up Power system Questions. Answers needed soon as blackout expected!!!!!! I am putting together a backup power system. I'm modifying an old ups to hold two 7AH batteries twelve volts, in parellel, to run my main filter during a blackout. What I want to know is how long will I be able to run my main filter, which consumes 33 watts at 230V AC. More importantly, I have a 75AH battery. Can I connect that to the UPS, will it charge properly... Please tell me as soon as possible as we are expcecting power faliures which could last a long time... Please also tell me what I'd need to do if I can't hook up the 75AH battery directly... Thanks.

08/04/2007, 06:52 AM	#2
Bandsaw Registered Member Join Date: Jan 2005 Location: North Eastern Ontario (above Sudbury) Posts: 720	Well, since P (power) is equal to Volts X Amps, then at 230V, your 33W pump will draw 0.143A. Now figuring out what your 7AH battery is going to give you is hard to say. That all depends on the efficiency of your UPS. It takes a considerable current draw from a low voltage DC source to produce a 230VAc output (by straight transformer theory, that is 19:1 step up, so for every 1 amp out at 230Vac, you need 19A input at 12Vac, for a straight transformer). It is not as simple as that as we are taking 12DC in, convert to AC, etc, but I think you the idea. The best thing to do is check the specs on your UPS. It should tell you there what its input current is at maximum output load. Then work the numbers from that. With reference to your 75AH battery. Again, you will need to check your specs on your UPS. Is the battery the same type as the one you are replacing (Lead Acid, NiCad, Lithium Ion). Not all batteries are charged the same. If 7AH battery and the 75AH battery are the same type, there should not be a problem. It will charge. If they are not the same type, you run the risk of an exploding battery or the battery giving off dangerous emissions. Just a word of caution. Dealing with electricity is always a dangerous game at any voltage. Unless you have complete competence in what you are doing, I would recommend getting a UPS designed specifically to connect to an external battery and follow the supplied instructions. __________________ VE3SZB Failure is not an option - It is a requirement if you expect to learn anything. Click on my home page button for pictures of my aquarium. Current Tank Info: 75g Display, CPR SM Aquafuge, 8g sump, 20g tall fuge, Maxspect R420R LED, KoralLin 1502 CaRa, EV-180 Skimmer

08/04/2007, 07:57 AM	#4
Bandsaw Registered Member Join Date: Jan 2005 Location: North Eastern Ontario (above Sudbury) Posts: 720	Out of curiosuity, where are you located? I ask because you are saying 50 Hz. This is only a guess. But a 7Ah battery should get you an hour or so?? If it's an older unit, then it's effenciency may not be that great. Newer UPS/Inverter have an effenency closer to 90% (means only 10% of the input power is used to actually run the UPS). Like I said, it is really only a guess. You should not overheat the UPS. It probably has a current limit circuit that would prevent it from overdoing it self. Important thing is to keep the leads to the battery as short as possiable and use as large wire gauge as you can. __________________ VE3SZB Failure is not an option - It is a requirement if you expect to learn anything. Click on my home page button for pictures of my aquarium. Current Tank Info: 75g Display, CPR SM Aquafuge, 8g sump, 20g tall fuge, Maxspect R420R LED, KoralLin 1502 CaRa, EV-180 Skimmer

08/05/2007, 08:39 AM	#6
Bandsaw Registered Member Join Date: Jan 2005 Location: North Eastern Ontario (above Sudbury) Posts: 720	What you can do is if you have access to an Ampmeter, connect the ampmeter to the battery and run your pump (with the UPS unplugged). Measure the current being drawen from the battery. That will tell you how long you can expect the battery to last. Yes, I beleive the AH rating would be 14 AH when connected in parallel like that. Just use some caution when trying to charge the big battery. Monitor it. Again, if you have access to an Ampmeter, the Ampmeter will tell you how hard the battery is being charged and if the UPS is stopping the charge when the battery reaches its nominal charge (13.23Vdc). Good luck with it all. Having a backup sure is nice. __________________ VE3SZB Failure is not an option - It is a requirement if you expect to learn anything. Click on my home page button for pictures of my aquarium. Current Tank Info: 75g Display, CPR SM Aquafuge, 8g sump, 20g tall fuge, Maxspect R420R LED, KoralLin 1502 CaRa, EV-180 Skimmer

08/04/2007, 07:06 AM	#3
fishquaria Registered Member Join Date: Jun 2007 Location: Sri Lanka Posts: 170	Jeff, thanks so much for your reply, very comprehensive. The ups runs on sealed lead acid batteries. The ups is quite old, so you can't really see the specs. All I can tell you is its 230V at 50Hz. Please help me calculate at least a rough estimate of how long my pump will run on the two 7AH batteries connected in parellel. Please also tell me if it is then safe to hook up a car battery considering that the batteries in the UPS are sealed led acid and the car battery is a wet lead acid battery. I am worried that if I do connect my UPS to the car battery the ups might over heat, is this a possibility? Please please help me as I'm not home most of the time to attend to the fish in the event of a power faliure and leaving emergency care to the people at home might leave my fish dead anyway... he he... please tell me all you can. I deeply appreciate all you've told me already... Thanks so much, Jeff...

08/04/2007, 09:26 AM	#5
fishquaria Registered Member Join Date: Jun 2007 Location: Sri Lanka Posts: 170	Colombo, Sri Lanka... But since it's 7AH X 2 in parellel, that effectively makes it 14 AH right? So what you're saying is that I can connect a car battery to it without any fear? Thanks for all the help... if there's anything else you can add please do so... thanks a million.

08/05/2007, 09:15 AM	#7
BeanAnimal Registered Member Join Date: Feb 2003 Location: Pittsburgh Posts: 20,772	Parallel batteries can pose a great danger. If a single cell shorts internally, the other cells will see the short and supply large amount of current. EACH BATTERY in a parallel circuit must have its OWN fuse. LARGE diodes can be used to prevent one cell from feeding another. Though, you will not be able to charge with the diodes in place. Cells of different sizes can pose an overall capacity problem in parallel. The larger capacity battery will carry the brunt of the load and discharge though its curve faster than it would otherwise. This is complicated but let me try to explain. (1) 50Ah and (5) 10Ah batteries = 100Ah (2) 50Ah batteries given the same load, the (2) 50Ah cells will last longer than the combination og (6) mixed cells. Is s generator out of the question? What lenght of power outage do you plan onm preparing for and what is your proposed current draw during the outage? Just 33W? What about heat?

08/05/2007, 10:06 AM	#8
fishquaria Registered Member Join Date: Jun 2007 Location: Sri Lanka Posts: 170	Luckily the ambient temperature doesn't drop below 26 degrees over here and highs are generally 34 degrees but that's an off day. So tank temp can easily be maintained at 27 degrees celsius with a heater and fans... (The heater is for when the A/C is on)... he he. I am now using a 75AH battery... Waiting to see the results... it's currently charging... Thanks for all your info and will get back to you.