Resmed DC Converter

ozalchemist · Post by **ozalchemist** » Mon Jul 16, 2007 3:31 am

Does anyone actually KNOW what this does?

Resmed start off by saying that it must be used witha 12V DC supply, but justfy it by making all sorts of references to AC inverters....

Anyone Know:

1. What is inside that black box on the DC converter that Resmed sell.

2. What the black box does?

I can't see, other than actind as a low voltage cutoff device, what the damn thing is therefore other than to generate revenue.

dsm · Post by **dsm** » Mon Jul 16, 2007 4:41 am

Oz, My understanding of what it is, is a pure sine wave inverter that converts 12vdc into 240vac mains power. Normal AC mains power is delivered as a sine wave.

The reason to use one is if you want to run the S8 with its heated humidifier. If you can do without the H/H you can run the machine of 12VDC. Resmed also sell a 'converter' that can take 12-24VDC and output 12VDC. This 'converter' will also switch off the supply to the S8 if the input voltage drops below 12v. That can happen if a battery starts to go flat and that in turn can also damage the machine.

The reason why it is pure sine wave (vs square wave) is that the square wave inverters damage the S8 power supplies. Many other brands can run ok with square wave inverters (they are cheaper to buy than sine wave inverters).

For those not familiar with a sine wave pattern - ripples on a pond are in a sine wave pattern. Square wave is I guess like the shape that you see if looking end on at railway sleepers.

DSM

ozalchemist · Post by **ozalchemist** » Mon Jul 16, 2007 4:44 am

The DC-12 has a Cigarette lighter plug on it... it's INPUT VOLTAGE is 12V, it's output voltage is 12V.

It is NOT an inverter.

The Resmed S* has TWO sockets on the back. One for 110/240V and one for 12V.

Resmed claim that you need to use their DC-12 adapter between a 12V source and the 12V socket.

An Inverter would be used between a 12V sourve and the 110/240 socket.

Which brings me back to my priginal point... hwta does the Resmed DC-12 do?

ozalchemist · Post by **ozalchemist** » Mon Jul 16, 2007 5:03 am

Having read around some more....

I can understand that the DC-12 reduces a 24V supply to 12V, but will it really matter if the 12V from a deep cycle battery drops off by a volt or so at the nd of the cycle?

What happens if a 240V supply browns out doen to 220V?

billbolton · Post by **billbolton** » Mon Jul 16, 2007 5:38 am

ozalchemist wrote:The DC-12 has a Cigarette lighter plug on it... it's INPUT VOLTAGE is 12V, it's output voltage is 12V.

The nominal "12V" DC electrical system in most automobiles is typically more like 13.5V DC. The Resmed DC-12 accepts a range of input voltages from about 11.5V (or so) to 24V DC and outputs a well regulated 12V DC output.

Resmed claim that you need to use their DC-12 adapter between a 12V source and the 12V socket.

As Doug noted above, amongst other things the DC-12 will cut off when the input voltage drops below about a preset level (which varies depending on whether you plug into a nominal 12V or nominal 24V supply) to prevent accidently deeply discharging a vehicle battery.

Which brings me back to my priginal point... hwta does the Resmed DC-12 do?

It provides a very stable 12V supply to the S8. Users with a good understanding of electronics can probably get away without using a DC-12 when powering an S8 from a low voltage supply. Its primarily intended for CPAP users who want a simple and foolproof solution to plugging an S8 into any arbitrary "cirgarette lighter" power source.

What happens if a 240V supply browns out doen to 220V?

The S8 uses a switched mode mains power supply which operates over a range from about 100V AC to 240V AC, at 50 or 60 Hz. Low mains voltage will not effect an S8 until it drops below 100V AC.

Cheers,

Bill

ozalchemist · Post by **ozalchemist** » Mon Jul 16, 2007 7:34 am

Okay... that makes sense.

So... I live in the wilds of Western Australia, where, in winter, the power can go out for as long as twelve hours. If this happens at night it makes it rather difficult to go to bed with a mains powered CPAP.

I want to get a reasonably large 12V gel cell and keep it charged with a 12v float charger and then use it to run my s8 (without the humidifier) when the power is out.

It will be a once in a blue moon thing. If i get a battery that is large enough (I have resmeds charts on current draw at various pressures) then I should be able to maintain 12V through a full night.

What do you think?

I don't mind buying the adpater if it is going to perform some service, but if it's just there to foolproof the process, then I'd rather just fork out for the battery.

Opinions?

dsm · Post by **dsm** » Mon Jul 16, 2007 5:31 pm

[quote="ozalchemist"]Okay... that makes sense.

So... I live in the wilds of Western Australia, where, in winter, the power can go out for as long as twelve hours. If this happens at night it makes it rather difficult to go to bed with a mains powered CPAP.

I want to get a reasonably large 12V gel cell and keep it charged with a 12v float charger and then use it to run my s8 (without the humidifier) when the power is out.

It will be a once in a blue moon thing. If i get a battery that is large enough (I have resmeds charts on current draw at various pressures) then I should be able to maintain 12V through a full night.

What do you think?

I don't mind buying the adpater if it is going to perform some service, but if it's just there to foolproof the process, then I'd rather just fork out for the battery.

Opinions?

billbolton · Post by **billbolton** » Tue Jul 17, 2007 1:24 am

ozalchemist wrote:I want to get a reasonably large 12V gel cell and keep it charged with a 12v float charger and then use it to run my s8 (without the humidifier) when the power is out.

Unless your tritation pressure is quite high, about 10 AH of capacity on a nominal 12v Battery will run an S8 for 8 hours or so, at or near sea level altitude.

Jaycar has a 26 AH deep cycle 12V gell cell battery.....

http://www.jaycar.com.au/productView.as ... &SUBCATID=

.... which looks good for your application.

I don't mind buying the adpater if it is going to perform some service, but if it's just there to foolproof the process, then I'd rather just fork out for the battery.

I bought a DC-12 to more or less to figure out what it did, rather than having a particular use for it.... but it has actually turned out to be useful on a number of occasions when I have needed to plug my S8 in a 12V supply of which I didn't/couldn't know the characteristics. At least with a DC-12 I know I'll get an assured 12 Volts, or get or nothing, out the output side. At around about A$80 or so, its cheap insurance.

By the way, make certain that with anything you wire up yourself to connect directly to an S8, you put the Positive (+) side of the DC supply on the sleeve of the power connector and the Negative (-) side of the supply on the pin of the connector..... this is opposite to the way that most DC powered devices that use that style of connector are wired!

If you put positive on the pin and negative on the shell of the S8 DC power connector you will kill your S8 INSTANTLY, and it will need to go to a service depot for repair.

Cheers,

Bill B.

Machine	Mask

Additional Comments: Airmini, Medistrom Pilot 24, CMS 60C Pulse Oximeter, ResScan 6