change over circuit for cpath machine

[shortbus=]

As a user of CPAP for over 20 years, I don't see the problem here. And my apnea is very bad. But if the power goes out during the night you wake and take the mask off, no problem. Even if I have to go somewhere away from home for just a few days I don't take my CPAP. I and you lived for many many years without one, so I don't understand the panic of one night without it.

 

[shortbus=]

Sealed lead acid (SLA) would be safe, but getting the capacity you desire would require large and/or multiple batteries.

Even the so called SLA batteries have a vent, to allow the pressure of charging to get out. They just have a sort of "check valve" to not allow liquid to leak. https://www.google.com/search?q=Sea...hUKEwjn9MnArJDzAhWvFVkFHSu4CMgQ4dUDCA0&uact=5

 

[MrDEB]

I am looking at maximum output of the power pack of the machine.
I looked at the output of the Resmed10 unit and it showed average is 53W maximum is 104w
just comparing what the average high and average output.

 

[MrDEB]

here is the data I am referring to.

 

[MrDEB]

after looking at several UPS power supplies and using one does not look good.
Considering just using a 24 volt power supply and 2- 12v SLA batteries w/ high AH rating.
going from 110vac converting to 24v dc then back to 110vac using a UPS supply.
A 24v battery charger mixed in.
Got to be cheaper than the $200-$500 price tag for a Li-ion supply?

 

[Visitor]

As a user of CPAP for over 20 years, I don't see the problem here. And my apnea is very bad. But if the power goes out during the night you wake and take the mask off, no problem. Even if I have to go somewhere away from home for just a few days I don't take my CPAP. I and you lived for many many years without one, so I don't understand the panic of one night without it.

I can't get by without mine. I feel horrible the next day if I have to go without it.

 

[tumbleweed]

going from 110vac converting to 24v dc then back to 110vac using a UPS supply.
A 24v battery charger mixed in.
Got to be cheaper than the $200-$500 price tag for a Li-ion supply?

Huh?

So what was wrong with the $100 APC 450W UPS you linked to back in post #17?

A lot... my fault for not reading closer. See posts below.

 

[Visitor]

Huh?

So what was wrong with the $100 APC 450W UPS you linked to back in post #17?

This is only page 2 of the thread. There are still 4 more to go before it stops and we never learn if/what the solution was.

 

[MrDEB]

after reading other cpap users comments about using a UPS they basically say it won't run but a few hours maybe.
thinking hey I have a power supply (the cpap power supply) then just build a 24 volt battery charger that will float when the battery is fully charged.
Will post link to site with comments about using a UPS etc.

 

[Visitor]

This is only page 2 of the thread. There are still 4 more to go before it stops and we never learn if/what the solution was.

What we have here is a failure to communicate. The CPAP draws a maximum of a bit over 100 watts. The UPS is rated for 850 VA – for the moment, just consider that as watts. So, it can supply 850 watts.

Nowhere in the spec does it list watt-hours. That's what you need to know.

 

[shortbus=]

I can't get by without mine. I feel horrible the next day if I have to go without it.

Oh, I agree with your statement, but to got to the expense and having batteries sitting in the bed room is just over the top to me. Just my opinion.

 

[tumbleweed]

What we have here is a failure to communicate. The CPAP draws a maximum of a bit over 100 watts. The UPS is rated for 850 VA – for the moment, just consider that as watts. So, it can supply 850 watts.

Nowhere in the spec does it list watt-hours. That's what you need to know.

For some reason, I was misinterpreting that 850 VA number. Don't know what I was thinking.

If you go onto the APC website you can get a lot more details, including run-time estimates, etc.
That model is rated "450W", and it'll supply that for about 2 1/2 minutes!

At 50W, it's still only good for about a little over an hour. Looking at the thing, that pretty much makes sense.

 

[Nigel Goodwin]

after reading other cpap users comments about using a UPS they basically say it won't run but a few hours maybe.
thinking hey I have a power supply (the cpap power supply) then just build a 24 volt battery charger that will float when the battery is fully charged.
Will post link to site with comments about using a UPS etc.

It's pretty easy to connect much larger external batteries to a UPS, and there are lot's of examples of how to do so on the Internet and YouTube.

It might also be a good idea to actually measure what the CPAP takes? - as the printed values are probably just 'worst case' (cover their ass figures), and not actual real values.

 

[MrDEB]

I looked at the cpap battery packs ($300-$600) and they all use a LI-ion battery
The UPS power supplies use SLA batteries.
Issue with the UPS power supplies, they take 110v ac convert to 12v dc to charge the batteries then convert the 12vdc back to 110v ac.
I am looking at using the cpap power supply only if it can charge the 2-12v SLA batteries. The charger must have a float charge ( output about 1 amp charge after the batteries are fully charged).

 

[Visitor]

For some reason, I was misinterpreting that 850 VA number. Don't know what I was thinking.

I see exactly how it happened, because I fell into the same trap – you followed MrDEB down the wrong path.

Here's a data point for a reality check. A NPW36-12 gel cell (SLA) is a commonly used battery in consumer UPS supplies. These batteries are 12 volts, and are rated from 7Ahr, which equates to 84 watt-hour. My CPAP, which operates from 12 volts, will run about 3 – 4 hours from one of these cells (remember, operating current is a function of output pressure, so YMMV).

I have a specialized Belkin UPS that contains one of these cells, and is 120VAC in / 12VDC out, which I use to power my CPAP. I suspect this UPS was designed to power network gear for a VOIP phone system, but it's a good but not perfect solution for my needs.


I have also used an APC USP with one of these cells in it, where I have tapped an output directly across the 12 volt battery (the same type NPW36-12 cell). Probably not recommended as it's probably not completely isolated from the AC line voltage, but it does avoid the 12VDC --> 120VAC --> 12VDC conversion losses. Only only quirk is that the UPSC beeps when the power fails, so it's necessary to roll over and press the OFF button to shut off the unneeded UPS circuitry when the power fails.

 

[Nigel Goodwin]

Only only quirk is that the UPSC beeps when the power fails, so it's necessary to roll over and press the OFF button to shut off the unneeded UPS circuitry when the power fails.

That was an issue I hadn't considered

However, presumably a pair of cutters would cure that.

 

[Visitor]

I am looking at using the cpap power supply only if it can charge the 2-12v SLA batteries. The charger must have a float charge ( output about 1 amp charge after the batteries are fully charged).

Why would you expect the CPAP 24 volt supply would act as a 24 volt battery charger with trickle charging to boot? Because that's what you want it to do?!?

 

[MrDEB]

was just contemplating why not use the cpap power supply? it isn't big enough.
Here is my proposed plan- use 2-12v SLA batteries 15-20AH rating = aprox $150 or less for both
a smart charger 24v 2.8a 80w charger = $49.75
a change over circuit to switch from line power to battery power = $25? either the LTC4412 CIRCUIT OR A 24V RELAY. Note the relay would be energized 24/7
this should work and run the cpap for 10-12 hours estimate.

 

[Nigel Goodwin]

Note the relay would be energized 24/7
this should work and run the cpap for 10-12 hours estimate.

I've had a mains powered relay (on a plug-in octal base) permanently powered for over 25 years, it used to switch the power (for lights and certain specific sockets only) to my long defunct 2KW generator if the power dropped out. And of course if the mains comes back on, the relay re-energises, and switches back to the mains - nicely preventing any catastrophic issues.

It's never failed in all that time - and it's simply mounted inside a plastic box, pushed in an octal socket (so would be easy to change if ever required).

 

[Visitor]

Max power draw = 104 watts -->

Max current = 104w/24v = 4.33 amps.

If battery rating = 15AHr, 15AHr/4.33A = 3.46 hours

If battery rating = 20AHr, 20AHr/4.33A = 4.62 hours

This is worst case, but you can't assume "average" values, as current draw depends on CPAP pressure.

========≈================================

Charging

Assume 20AHr battery is flat after operating for 8 hours (which it would be under average or worst conditions).

Must charge about 20% greater than needed, in a 16 hour period.

(20AHr × 120%)/16Hr = 1.5 amp charge current minimum to reach full charge in 16 hours.

========≈================================
Conclusion

You may get between 3.5 – 9 hours of operating time from a full charge, depending on CPAP pressure – a fractional to full night's use from a charge.

The proposed 1.8 amp charger will replenish is batteries in less than 16 hours, if power has been restored. The system will not support more than one night's service in an extended power failure.