Batteries, converters and warrantee

[Twentysix]

Hi guys, would like some info from the more experienced. Someone posted here about the batterygeeks website. They offer batteries and converters/inverters (no idea what the difference is) that would also work with my Resmed S9. Resmed themselves do offer a converter, which is twice the price of the batterygeeks one, but they have told me that using another brand would 'potentially influence the warrentee' on the machine. They could not tell me why it was twice the price (like would it be twice as good, or last twice as long?), nor did I get any answer on my question if Resmed sells batteries too. Anyone experiences with my machine in combination with converters and batteries? I'm an avid camper and hiker, so would like to get that sorted in order not to have to resign to sleeping lousy on holidays. Please share!

[TooGroggy]

You can find Resmed's specs here: http://www.resmed.com/au/assets/documen ... lo_eng.pdf

As long as the inverter (edit: i.e., the box that converts 12V of DC current into 120V AC current) meets the minimum requirements they specify, you shouldn't have any problem.

I read somewhere else that Resmed had recently announced the availability of a converter (i.e., a box that converts 12V of DC current into what the S9 needs). But the price is reportedly $150.

[Twentysix]

You can find Resmed's specs here: http://www.resmed.com/au/assets/documen ... lo_eng.pdf

As long as the inverter (i.e., the box that converts 120V of AC current into what the DC current that the S9 needs) meets the minimum requirements they specify, you shouldn't have any problem.

I read somewhere else that Resmed had recently announced the availability of a converter (i.e., a box that converts 12V of DC current into what the S9 needs). But the price is reportedly $150.

Yes, that is the one they are offering at the moment for A$135, but will be A$145 later on. So a converter = inverter? And you would still need a battery, unless you want to sleep next to the car with the cigarette lighter as your power source.

[TooGroggy]

Sorry, it appears that I mis-spoke.

An inverter connects to a battery to deliver 120V AC current. With an inverter, you would still need your standard S9 AC adapter.

A converter connects to a battery to deliver the power the S9 needs. With a converter, you will not need the standard S9 AC adapter.

Because a converter goes directly from the battery to the machine, using one is more efficient that the inverter which involves going from the battery to the inverter to the machine. As a crude approximation, you should figure that the converter will deliver 80% or more of the juice of the battery whereas the inverter will deliver 64% (80%x80%) or less.

[billbolton]

As a crude approximation, you should figure that the converter will deliver 80% or more of the juice of the battery whereas the inverter will deliver 64% (80%x80%) or less.

That's far too crude. Contemporary, good quality switching mode inversters and power supplies which are suitabe for running an S9 are typically ~95% efficent, so number is more like 95% * 95% = ~90%

A DC to DC Converter will be ~95% efficent, so the difference between the approaches is nowhere near as great as you are suggesting.

Cheers,

Bill

[Twentysix]

I really appreciate your responses, but am afraid I'm getting more confused now. What is it I need to get to be able to use the S9 with a battery? And does anyone have experience with this machine and battery use?

[HoseCrusher]

The simplest way to do this is to use a device that takes battery voltage and raises it up to the 125 volts needed by the machine. If you get a device that offers true sine wave frequency, and has enough capacity to meet the maximum requirements of your machine, it will be just like plugging it into the wall.

The machine has a controller that runs on DC. In order to provide accurate pressure and flow, the voltage of the controller has to be held within a very narrow range. Since batteries in vehicles are subject to wide voltage fluctuations, you often can't simply plug the machine directly into the battery. One way to visualize this is to look at your headlights. With the engine off, when you first turn your headlights on they are quite bright. However, after leaving them on for some time, they dim down. If your goal was to have constant brightness from your headlights (or constant pressure from your xPAP machine) simply running off the battery will find you short of your goal.

[timbalionguy]

If at all possible, go with the DC-DC converter. Despite what Billbolton says, there are other system losses to take into account, which will put the overall system efficiency well under 90%. Forthermore, if you don't need your humidifier, you don't really need to run the unit on AC power. (most camping situations do not need a humidifier, as the outdoor humidity is higher at night while outside.) It is also safer to keep down to low DC voltages. This eliminates any shock concerns if you should get dew on line voltage part of an AC inverter system. You will aso save weight by needing s smaller battery and one less power supply 'brick'.

[billbolton]

Despite what Billbolton says, there are other system losses to take into account, which will put the overall system efficiency well under 90%.

What specifically are these other system losses then?

Forthermore, if you don't need your humidifier, you don't really need to run the unit on AC power.

The H5i runs on DC power. Actively using it humdifier will chew through pretty much the same amount of energy whether the external source is AC or DC.

Cheers,

Bill

[greg-g]

An interesting discussion, but another overlooked issue.
While the Resmed Dc-Dc converter will be more more efficient even if only by a small margin, more convenient, and probably safer, it will be unique to the Resmed S9, have no other applications. A DC to mains power converter can be used for any application within its power range including other xPAP machines.

[knathdrak]

Have any of you tried using something like the following?

http://www.cpaptravelbatterypack.com/re ... -pack.html


I also love to go camping / hiking and I work my local Renaissance fair (so every weekend for 2 months camping out there).
I'm looking at my options.

I can get the resmed converter, I can get a generic DC-DC converter, both of these will also require the purchase of a battery (and it seems a marine deep cycle would be the best) for $150+

This little kit mentioned above looks to be cheaper, but any experience on how it works? Yes, it will only work for 1-2 nights (a marine battery with enough amp hours would work longer) but just weighing options and looking where to start.

[rested gal]

Twentysix, here's a link to even more ideas:

LINKS to Battery operation, camping, power outage
viewtopic.php?t=9682

[Patrick A]

RG
Thanks for posting the link.

[Twentysix]

Thanks gals and guys, will check out all provided.

[BigNortherner]

Do check the input power requirements against converter/inverter.

Invertors vary in the quality of the output power – some equipment wants closer to a pure sine waveform than other equipment, depends on equipment type and specific design.

If your machine has a DC input jack, as for example the Remstar classic does, I’d go with the DC cord sold by your manufacturer as that is more straightforward in general. (I know nothing about your machine’s DC input, but my Remstar classic’s DC cord does not appear to be a converter, just a cord with an electrical filter in it. Presumably my machine copes with the DC voltage difference. (Mobile generating systems, be they auto, airplane, train, etc. will have more power spikes to load switching, but that is what the filter in the cord is for. With generator off the power should be smooth, just decreases in voltage as battery depletes.

There was a thread some months ago in which I and others pontificated on the amount of power needed to run the machine with and without an inverter. My machine takes much less power than the nameplate would suggest, though that may depend on pressure setting. My humidifier only runs on AC so I do without it, I’ll cobble up a passive passover humidifier if I need to (hmm – they used to be sold for CPAP use), even a dish of water near the machine’s air intake might be helpful.