Going to hack a large battery into one of my old UPS units. Need help picking UPS

[Craig-Tx]

Ok, so I have a handful of old UPS units that I've collected over the years. Every one of them has bad or no batteries.

My need:
I have sleep apnea and use a CPAP. twice in the last couple of months, I've been rudely woken up by a complete lack of air due to a power outage. (Not pleasant.) In addition, both times the power was out for at least an hour.

I need a UPS that can supply a relatively low amount of power for a LONG time.
Typical load will be less than 30 W. Possibly up to 100 W at rare times.
Ideally I'd like it to last 8 hours.

So I'm thinking a UPS with approximately 50 amp hours of battery should be sufficient. (All are ballpark, numbers, but I figure 50 ish AH should be a good start.

Power outages should be rare, so if it takes several days to recharge the battery, that should be ok.

I know you can generally swap a large AGM battery into a typical UPS with some limitations.
- Same battery voltage
- Some UPS units are cheap and the voltage regulators don't have great heat sinks as they simply plan on it only running for a few minutes

What I have
1: APC Back-UPS 250
- Old unit
- single 12V 7AH battery.
- Looks like: PIC

2: APC Back-UPS ES 500
- Newer Unit
- single 12V 7AH battery.
- Looks like: Amazon

3: Conext CNB900
- single 12V 12 AH battery
- Looks like: PIC

4: Minuteman MBK750E
- Dual 12V 7AH battery
- Looks like:PIC

My plan:
If I used UPS # 1-3, I'd get a single 12V 55 AH battery such as:
Mighty Max ML55-12

If I used UPS #4, I'd get two 12V 35 AH U1 batteries such as:
Mighty Max ML35-12

So far, I'm leaning towards UPS #4. but I don't know enough about MinuteMan UPS. Are they good? From what I read, this one has AVR and even a cooling fan, so the longer run times might not be a problem.
Of course with the fan, it might be an issue as this will be in the bedroom.

Has anyone done this with any of the above UPS units? success? failure?

Also, for those who know, Mighty Max batteries? any good? Better recommendation for a similar price point?

Thanks for your help.

-craig

 

[freeskier93]

The only thing I can give you help with is battery sizing. 30 watts at 12.6 volts is 2.4 amps, therefore a 50 Ah battery will give you nearly 21 hours of continuous use. Even at 100 watts all the time thats just over 6 hours.

 

[Craig-Tx]

The only thing I can give you help with is battery sizing. 30 watts at 12.6 volts is 2.4 amps, therefore a 50 Ah battery will give you nearly 21 hours of continuous use. Even at 100 watts all the time thats just over 6 hours.

Exactly. As I stated, I was shooting for at least 8 hours. The 21 hours will likely be cut in half as a lot of the power is lost in the UPS converting it back to 110 AC. Plus, I'd prefer to not drain the batteries completely, but I will to get a good night's sleep.

In the winter I use the heated humidifier on the CPAP. That's when the load is increased to roughly 100 watts. I probably won't get more than 3-4 hours realistically in that use case with a 50 Ah battery. But that's a LOT better than what I have now.

But thanks for running the numbers; you helped confirm the math I did in my head.

 

[sparks56]

Note: does your CPAP have DC cable capabilites such as the Remstar M series. you may be better off going to a DC supply, as going through an inverter limits the time available for use. If you are tech, using a power converter from AdaFruit and a RaspberryPi can make a seamless switch if a power goes out.

 

[Craig-Tx]

Note: does your CPAP have DC cable capabilites such as the Remstar M series. you may be better off going to a DC supply, as going through an inverter limits the time available for use. If you are tech, using a power converter from AdaFruit and a RaspberryPi can make a seamless switch if a power goes out.

I have a ResMed S9. Unfortunately it uses 24V natively. I do have the 12V power brick, and I know it will use quite a bit less power. The downside is that I would have to power the unit off the battery all the time, whereas a commercial UPS will simply connect the line voltage to the output and switch to battery as needed.

I originally thought about setting up a 12V supply and a battery maintainer to keep the battery charged. During an outage, I'd have to manually plug in the 12V supply and then try to get back to sleep.

I don't believe that I can seamlessly switch between the 110V supply and the 12V supply, as it uses a proprietary 3-pin plug that also has a comm line in it to monitor the power supply status.

Also, the other advantage of a basic UPS setup is that I can also plug in my alarm clocks and even a lamp for emergency use.

The good news is that if I know the power is out for a long time, I am planing on a method to disconnect the batteries from the UPS and use them as a simple 12V supply for my CPAP using the DC plug. That is if I know it will happen before I go to bed.

 

[maddie]

I hope I,m not imposing too much or hijacking your thread, but I have a similar need for a low power/long use backup for an aquatic use. Definitely not a life issue as your situation, but still important for me as electricity disruptions occur every week, sometimes for a few hours.

I use an APC 550 for standby and am thinking of connecting a large capacity auto battery to extend the running time, but at present with the standard battery, the unit switches off after about 30 mins and has to be powered on again. This cycle repeats until electricity is restored.

Do you have any explanation as to why and is there anything I can do to remedy the situation?

 

[LTC8K6]

Just watch out that the larger battery does not overburden the charging circuit of the UPS.

 

[LTC8K6]

I hope I,m not imposing too much or hijacking your thread, but I have a similar need for a low power/long use backup for an aquatic use. Definitely not a life issue as your situation, but still important for me as electricity disruptions occur every week, sometimes for a few hours.

I use an APC 550 for standby and am thinking of connecting a large capacity auto battery to extend the running time, but at present with the standard battery, the unit switches off after about 30 mins and has to be powered on again. This cycle repeats until electricity is restored.

Do you have any explanation as to why and is there anything I can do to remedy the situation?

Sounds like it may be overloaded? Is it making a beep or a tone?

 

[maddie]

Sounds like it may be overloaded? Is it making a beep or a tone?

The load is only around 15 watts. About 29 mins with no sound and then it beeps about 3-4 times about 1 minute before shutting off. When I press the on button, it repeats the 30 min cycle.


By the way, anyone else here seeing the message below when trying to access page or quote links. It only started about 2 weeks ago and is intermittent.


Bad Request

Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit.
Cookie
/n

 

[Craig-Tx]

I hope I,m not imposing too much or hijacking your thread, but I have a similar need for a low power/long use backup for an aquatic use. Definitely not a life issue as your situation, but still important for me as electricity disruptions occur every week, sometimes for a few hours.

I use an APC 550 for standby and am thinking of connecting a large capacity auto battery to extend the running time, but at present with the standard battery, the unit switches off after about 30 mins and has to be powered on again. This cycle repeats until electricity is restored.

Do you have any explanation as to why and is there anything I can do to remedy the situation?

Not a hijack at all. In fact, you're looking to do essentially the same thing. And while not life or death for humans, it certainly could be for those fish.

I wish I could explain the 30 min. Two possibilities come to mind:

1: The output transistors are getting hot. Many smaller UPS units are only designed to run for a short time. The output Transistors use a simple block of aluminum as a heat sink. While a block of aluminum is good at absorbing heat, it certainly doesn't dissipate it well. So it's a good heat sink for something that will only heat up on rare occasions for a short time, and then be off for a long time allowing the block to cool.

2: APC put some 'Smarts' into the unit, and internal software has a 30 min timer. There are a few good reasons for this. The heat sink issue above is one. Prolonging the battery life is another. While sealed lead acid batteries are designed to be drained and recharged, they still don't like to be completely depleted. Stopping the discharge while the battery still has a half charge will go a long way to keep batteries healthy.

Ok three possibilities...
3: You actually are draining the battery to a threshold. You stated your load only pulls 15 W. If the UPS was 100% efficient, after 30 min, that would only be about .625 AH. Assuming it uses a standard 7.2 AH battery, that's only 10%. BUT... the UPS uses some power as well. And if your battery is older, it may only have half of it's original capacity.

Of course if as you say, you can simply hit a button and it will run for another 30 min, then #2 is most likely.

What I would do is put a volt meter on the battery and pull the plug and chart the voltage every few min to see where it is when you first pull the plug to where it is when it shuts off. Then hit the button and watch the voltages again. This site has a good state of charge chart based on voltage level. http://modernsurvivalblog.com/alternative-energy/battery-state-of-charge-chart/

Let us know what you find.

 

[maddie]

Not a hijack at all. In fact, you're looking to do essentially the same thing. And while not life or death for humans, it certainly could be for those fish.

I wish I could explain the 30 min. Two possibilities come to mind:

1: The output transistors are getting hot. Many smaller UPS units are only designed to run for a short time. The output Transistors use a simple block of aluminum as a heat sink. While a block of aluminum is good at absorbing heat, it certainly doesn't dissipate it well. So it's a good heat sink for something that will only heat up on rare occasions for a short time, and then be off for a long time allowing the block to cool.

2: APC put some 'Smarts' into the unit, and internal software has a 30 min timer. There are a few good reasons for this. The heat sink issue above is one. Prolonging the battery life is another. While sealed lead acid batteries are designed to be drained and recharged, they still don't like to be completely depleted. Stopping the discharge while the battery still has a half charge will go a long way to keep batteries healthy.

Ok three possibilities...
3: You actually are draining the battery to a threshold. You stated your load only pulls 15 W. If the UPS was 100% efficient, after 30 min, that would only be about .625 AH. Assuming it uses a standard 7.2 AH battery, that's only 10%. BUT... the UPS uses some power as well. And if your battery is older, it may only have half of it's original capacity.

Of course if as you say, you can simply hit a button and it will run for another 30 min, then #2 is most likely.

What I would do is put a volt meter on the battery and pull the plug and chart the voltage every few min to see where it is when you first pull the plug to where it is when it shuts off. Then hit the button and watch the voltages again. This site has a good state of charge chart based on voltage level. http://modernsurvivalblog.com/alternative-energy/battery-state-of-charge-chart/

Let us know what you find.

#2 seems most likely as these cycles can repeat for several hours. In fact, if I turn it off and back on before the cycle ends, I hear no beeps. This would imply no overheating and no low charge in the battery. The inability to leave the system unmanned is the problem. My plan was to attach a bigger battery allowing longer run times, but a timer will have to bypassed for this to work. Will try and test voltages over time.

Do you have any similar problems with continous use?

I guess I need a dumb UPS.

 

[Craig-Tx]

Do you have any similar problems with continous use?

I guess I need a dumb UPS.

So far... No. Honestly, I've never run any of these UPS units for an extended time. Until now! And it's running great!

So to fill in everyone on my progress:
I decided to get the two U1 batteries in my original post. I figure that would be the most versatile. I can either put them in series for 24 V to use with the MinuteMan UPS, or put them in parallel for 12V for the other units.

If I go with a 12V one, I'll likely use the APC 250 as it is the oldest and most sturdily built. I opened up them all and found that the APC ES-500 and Conext unit do simply use a block of aluminum as a heat sink. The APC 250 seems to use, while not a great heat sink, at least something designed to dissipate the heat.

I am so far unable to open the MinuteMan (other than the battery compartment) .. For a stupid reason. The screws are recessed too far, and I haven't bothered to go buy a long screw driver. But the MinuteMan does have one thing going for it. It has a fan!!!

So the batteries arrived yesterday. To start, I set it up in a 24V arrangement and connected them to the MinuteMan. The UPS immediately went to work topping off the charge. I let it run overnight, and this morning, the batteries were sitting at 28.1V and the charging circuit was still pushing 0.09 A into them. Not sure if it's still topping off the last few %, or if it will continually float it that way. I'll track that more later between the devices.

In any case, I called the batteries full and decided to do my first rundown test.

I moved the setup to the garage (mainly because I didn't want to listen to the beeping all day. - Will have to eliminate that for my purpose.) And connected the following.

Plugged the UPS into the wall, and plugged a mechanical appliance timer into the UPS with a 60W incandescent light plugged into the appliance timer. I setup the timer to click the lamp on at 12:00 and set it's time to just before it. As soon as the light went on, I unplugged the UPS from the wall.

So far... So good. The light is still lit. The UPS is still beeping. The timer currently reads nearly 3:00. The MinuteMan UPS fan is blowing slightly warm air, but not hot at all.

The way I have it set, when the UPS shuts down, the timer will stop turning, and I'll get a rough run time (the timer will only give me roughly a 30 min accuracy,) Before I plug it back in, I'll put an amp meter in line and measure the voltage and current to evaluate the recharge capability of each.

Then I'll repeat the process with the APC 250.

Well, this post went longer than I expected. I'll fill everyone in later on more results as they come.

 

[LTC8K6]

Is it possible that the APC Powerchute software would allow you to change some of the APC settings?

 

[Craig-Tx]

Is it possible that the APC Powerchute software would allow you to change some of the APC settings?

It is possible that the software will allow me to disable the beeping. However, I have not been able to get the MinuteMan SentryPlus software to recognize the UPS. Apparently, while it has a USB connection, internally, it is a USB To RS232. I have a forum post on the MinuteMan website for assistance with getting that working.

 

[Craig-Tx]

Update:

Well, I let the MinuteMan UPS run on battery for a while, waiting for the thing to simply shut off. I'm not sure it will.

I ended it this morning when I realized it had drained the batteries to 21.8V (10.9V each). (I hope I didn't badly damage my new batteries.)

However, that was after burning a 60W light for 21 hours!!!! I can only assume that the light didn't truly pull 60W on a modified sine wave. If so, those batteries have WAY more than 35 AH capacity.

So before I get chastised for over draining the batteries, I didn't mean to go that far. They were over 12V each when I went to bed and I assumed the UPS would shut down. Ohh well, live and learn.

 

[Craig-Tx]

Update on the MinuteMan. So It's been about 2 and a half days and it's finally got the batteries up to close to the float voltage. They are at 28.7V now. It's been slowly charging at roughly .5 Amp. Which as rare as the power goes out, this isn't a real problem. I should be able to tolerate a few days to recover. The only real problem is that it has stopped charging twice when the batteries weren't close to full. (I think after about roughly 24 hours it decides to give up.) Simply unplugging and replugging resets it. But that means I have to monitor it more closely than I'd like. If I decide to use this UPS, I'll likely have to get a good battery charger to put on it following a big outage to do the bulk charge.

Anyway, things are progressing. Now that it's at the float voltage, I believe that means it's about 75% charged. (This has been a fun learning experience in battery charging, etc.) Once it's fully topped off, I'll repeat the process with the APC 250 unit. Curious how that will work.

 

[Craig-Tx]

They are at 28.7V now.

Correction. They are at 27.6V now.

 

[Craig-Tx]

Ok, this is getting out of hand. My office now has piles of UPS units (in various stages of assembly) Batteries, and meters just about everywhere...

So, MinuteMan status:
Works well, but I'll have to manually remove the buzzer. The software should be able to disable the alarm, but when I try to apply it, it fails to apply the setting.

APC 250
I tried the two batteries in parallel and connected to the APC-250 with a lamp plugged in. After unplugging, I let it run for 15 min or so and plugged it in.
I think on the discharge side, it would be great. Heat didn't build up at all. No alarm.
Charging on the other hand... Not so good. After the small discharge, I plugged it back in and it was only charging the 12V at .25 Amp. That would take 4 times as long as the MinuteMan. And honestly, may even be too small to reliably maintain the batteries.

APC Back-UPS 500
I had little hope for this unit anyway, but figured I'd give it a quick try.
I don't know what it didn't like, but it immediately complained as if the batteries were bad.


Now onto the Conext. But that may be another day.

 

[Craig-Tx]

Well,
Surprise, surprise. One of my least likely contenders is the winner.

I connected the batteries into parallel and connected them to the Conext UPS. Let it charge up and did a discharge test using the same light bulb as before.

I didn't let it go nearly as far down, I let it run for 12 hours just to make sure it would endure a lengthy time. No problems there. Final voltage after 12 hours was 12.21. That was not a resting voltage, but while the load was still drawing current. So it still had plenty of juice left after that.

The charger of the Conext is where it won.
I plugged it back in and it started charging at over .75A. Over 30 hours later, when the battery was at 13.3 V, it was still pushing over .6A. (Although the MinuteMan could charge faster, .50A @ 24V compared to only .75A at 12V, it kept shutting off the charger every 20 hours or so.)

After more testing I can also explain my long run times. Turns out the bulb I though was 60W was smaller. The writing on the bulb was worn and smudged a bit, but I'm guessing it's either a 25W or 30W bulb.

With the UPS drawing power from the battery, the test bulb pulled 1.81A, a 40W bulb puled 3.14A, and an actual 60W bulb puled 4.43A. With no load, the UPS alone pulled 0.71A

Anyway, the other benefit of the Conext is the native 12V arrangement. Being that I am sticking with that, I purchased a cigarette lighter socket to add to the battery box for the nights when I know power will be out for a while. I'll disconnect the UPS and simply plug my CPAP in using the 12V adapter. That will be more efficient. Also after a long battery use, I can use a normal 12V battery charger to recharge the batteries more efficiently.

As for real CPAP power usage while plugged into the CPAP,
Without the humidifier on, the Conext was drawing 1.5 - 2.5A (Higher amperage when I inhaled, lower when I exhaled.)
With the humidifer on about a medium level, approximately 3 - 4A
Maxing out the humidifier (which I likely won't do) pulled close to 9A.

In any case, my original estimates were very close and my math still holds. Even maxing out the humidifier I should be able to get an 8 hour night of sleep. Realistic run times and I should be able to get 2 nights easily.

Hope this helps others out there.