My Battery Rig - Power Measurements

[ca_hosehead]

I built a battery backup based on John B Fisher's excellent design:

viewtopic/t49115/viewtopic.php?p=449334

I get a lot of power outages late at night so I needed something that would keep the machine running without waking up suffocating and switch the power over.

I use a humidifier, so I needed something that would handle the power requirements. If the power was off when I went to bed I would know to turn humidification off, but I was hoping for a system where I would wake up and wonder, "Did the power go off last night?"

To figure out what kind of power the machine was actually using bought a "Watts Up" inline power meter:

http://www.powerwerx.com/digital-meters ... nline.html

Picked it up off ebay for about $50. It's a nifty little thing that gives you a lot of information on what is actually happening with the electrical system. It's made for people that run remote control planes, boats and cars. I found the information very useful.

I went with a 100 AH battery. I got an AGM battery because it does not leak acid or vent flammable gas. It was $100 off Craigslist.

I went with a more powerful battery tender:

http://batterytender.com/marine/power-t ... at-5a.html

This one puts out 5 amps. My tests indicated that my rig was pulling 3 amps on average with climate control turned on and I thought that the beefier charger would do better.

I selected a Battery Tender because it was what John used, but also because it was one of the few chargers that talked about using the battery while the charger was attached. Other chargers either didn't mention it at all or said, "Don't do it."

I put the components into the bedside stand and out of sight.

Results are very good. The battery does not discharge significantly overnight. The battery tender stays in float mode and barely gets warm.

Power requirements for heated vs unheated do vary dramatically. The machine pull about 3 amps per hour with heat and 1/2 amp per hour without heat.




For electrical geeks, here are detailed results from three nights:

Resmed S9 with heated humidifier and heated tubing
Resmed DC Adapter
Altitude 1000 feet
Pressure is set to "Auto" with a 12 minimum and 20 maximum.

ah = amp hours
vm = Voltage minimum, lowest voltage recorded during the run
ap = Amp peak, highest amps for the period
v = Voltage across the battery in the morning (with the charger still attached)
wh = watts hours used during the run


Aug 27
8:36 run time
24.85 ah
12.78vm
13.33v
6.52ap
323wh
12.2 median pressure
Climate control 85 degrees


Aug 28
8:21 run time
13.3 v
12.25 vm
80.2 wp
24.8ah
6.34ap
80.2 wp
12.1 median pressure
Climate control 85 degrees

Aug 29
8:27 run time
4.5 ah
60.3 wh
2.87 ap
12.74vm
37.5wp
13.28v
12.1 median pressure
Climate control off

[archangle]

To figure out what kind of power the machine was actually using bought a "Watts Up" inline power meter:
...
I went with a 100 AH battery. I got an AGM battery because it does not leak acid or vent flammable gas. It was $100 off Craigslist.

Good info. You're going to tempt me to spend money with that power meter.

Wow, climate control does eat the power. I'd be very interested in results using heated humidifier, but without the heated hose.

Thanks for the great info.

[JohnBFisher]

It's great to see that others have taken my post and run with it!

That's a great approach to checking the amperage requirements, be accurate and safe. I like it.

I'm fortunate that I live in an area that does really require humidification. When I use a humidifier, I just use it in passover mode. So, I could afford the smaller setup. I did want to be able to go several nights without power, which sometimes we need.

I normally just run my unit once a month off the battery - to validate the system works. But I like the idea of always using it off battery. I might do the same.

One reason I suggested a modular approach is that you can readily add/change pieces as needed. If the battery is not strong enough, you can upgrade it. If the charger is not strong enough, ditto. It makes the whole thing a lot more adaptable. The closed case over the battery also makes it much better for an indoor application.

Thanks for your input to the 'cause'!

[GumbyCT]

Good job hosehead. There is always someone looking for a way to power their machine from battery. I'd say 100AH battery should hold you over for awhile

My biggest jump starter is 22AH but then I use passover humidifier this time of year and prob would during the winter if/when using battery power.

I like that meter too. Good Job

[ca_hosehead]

John I would be interested in knowing how your system behaved in a UPS type configuration. All of the solutions that I have seen are focused on a situation where you know that you are running off DC before you go to bed. Being able to sleep straight through a late-night power outage would be great for a lot of people.

If I get motivated I will buy some SAE connectors and see what the output of the charger into the system is. I suspect that the charger is supplying the power that the CPAP needs overnight and the battery is not being discharged. This would be ideal as it would extend the life of the battery.

You know I think there is a market opportunity here for some entrepreneurial spirit.

There would be a box. It would have one A/C wire that went into the wall. Two wires would come out of the box and attach to a deep cycle battery (that the user would provide.) The box would have a cigarette lighter socket. You would plug your CPAP's DC cord into the lighter socket.

When A/C was available the box would have two functions. The lighter socket would supply DC and run the CPAP. The wires that ran to the battery would charge the battery.

When A/C was not available the box would connect the battery to the lighter socket and supply power that way. Changeover would happen seamlessly.

When power was restored, it would simply switch back and use the A/C to supply the CPAP and re-charge the battery.

I found only one box that had a similar function:

http://www.westmountainradio.com/produc ... s_id=pg40s

It's designed for amateur radio power backups. It does not include a power supply. Price point is too high and it doesn't have the right connectors.

The box would need a pretty good sized, power output. My CPAP needs 6A to run but peaks around 7A so you would need to go above that, maybe to 10A run things like a bi-level at high pressure. After power was restored you would need to be able to run the CPAP and devote some power to battery charging as well. A smart engineer might be able to come up with a power partitioning design that devoted all the power to the CPAP when needed and then shunted power to the battery when the CPAP didn't need it.

[JohnBFisher]

... John I would be interested in knowing how your system behaved in a UPS type configuration. ...

Well, that's one of the reasons I picked the charger that I did. I have used it that way. It works. However, I had a smaller charger, so it does not provide the full power to drive my ASV system. It usually spends the next day topping off the battery.

But remember, my ASV system often acts as a ventilator and drives the pressure up to 25cm H2O. That's a lot more than what most people would need.

However, if you use the humidifier all the time ... not needed in my neck of the woods ... then you would definitely need the stronger charger.

... If I get motivated I will buy some SAE connectors and see what the output of the charger into the system is. ...

Again,that's why I designed the rig that way. If I want, The connector going into the box is a Y connector that has on SAE connector that connects to the box, another that connects to the charger and a car power outlet (aka the lighter socket). I used a fitting designed for motorcycle side bags to allow power in and out of the side bag.

If I know I might loose power, I will plug in the inverter, plug the ASV into the inverter and go to sleep. The charger provides some of the juice to drive the ASV. The battery provides some as needed. And I never need to awaken. If I bought and used the stronger charger, it would probably just provide the needed juice.

The advantage of this setup is that the box is secure against prying little fingers and dog noses. Or from accidental damage if something fell onto the battery.

Also, by coating the battery terminals and then covering the battery terminals, it helps protect the user/owner from either the corrosion from the battery terminal or from accidentally hitting the terminals. And the battery box is vented.

This all might seem to be overkill, but I've seen what can go wrong with these large batteries. I did not want to risk my luck to "It should work ...". Murphy and I are old friends. I've seen WAY too many things that should not go wrong proceed to fail spectacularly.

... I think there is a market opportunity here for some entrepreneurial spirit. ...

Agreed. However, I hope to spend some time making an Wiki article that will include:

1. A checklist to determine power requirements
2. A purchase checklist (based on the power requirements)
3. A set of step by step instruction sheets

That way, if someone does not feel comfortable with this type of thing, they can take the stuff to an automotive store to pick up most of the pieces. Some of it probably would need to be ordered for the average person (a lot of the power pieces are not readily found in stores). Then they can take the pieces / parts to an auto mechanic and have it put together. I will even try to get a few estimates of the time that will be needed to put together all the stuff.

That would make this project a lot more possible for even those that are not able to handle all the tools. Or for those who don't have the time. Or for those, who are just not sure about it...