intellipap fried but not toasted on car battery

[peterg]

oh dear, just had my new Devilbiss machice for 3 days and the area had a blackout. so, being addicted to CPAP I decided to hook the car battery up to the 12v input.
I plugged it in the immediatley smoke comes out of the machine. I immediately unplug the 12v (clever, arent I?)., and huff and puff on it (fanning the flames? or making a birthday wish).

I can't say for sure if I had the polarity wrong (I had tested iot on the multimeter). I was using thinner cables, the type that small appliances like external hard drives use.
So I guess it was one of those two things I did wrong.

the good news is the machine, miraculously, still works on normal mains (240v here) power and it worked well last night,
I had to run the machine for several hours without mask on to blow the horrible smells out of it.

I'm off to the shops today to get a 700MaH plus computer UPS, I dont trust 12v anymore.

anyone with any ideas what would have gone up in smoke in this machine?

the thing that threw me, apart from not re-reading the manual on 12v polarity, was the sign on the back of the machine where the 12v hole is, any other 12vDC devices I've ever seen have the icon with a plus sign, and a pointer to the inside or outside plug. this one had another symbol (there on page 2 of the manual for the keen observer). my bad (perhaps).

or are we not supposed to connect up 12v car batteries directly, and have to buy the manufacturers accessories.

anyhow, so far, I got away lightly. (a fear is if the partly fired circuit fries itself on mains power, blowing toxic fumes into my sweet dream time).

and I am a little peeved that they don't have fuses inside the machine for this kind of thing. it its polarity, it's easy to get wrong. (any other devices Ive done this with just dont power up with incorrect polarity) or, if it was the thin wires I was using, insufficient current.

I consider myself very lucky (so far)

[GumbyCT]

or are we not supposed to connect up 12v car batteries directly, and have to buy the manufacturers accessories.

That wouldn't be it, tho it does insure that sleep deprived people don't reverse the polarity and that it does work correctly.

My guess is what you smell is a burned diode whose sole purpose was to act like a fuse if/when someone reversed the polarity. Double check your work so you know what happened.

This is exactly why I recommend people NOT wait until they go camping or the lights go out to figure out how to hook up their equipment.

I don't think there is a one of us alive who hasn't tripped and fallen when we were learning to walk. I learn more when I make mistakes than when I don't.

[archangle]

The machine probably doesn't draw more than 4 amps or so on 12V when it's working normally. Unless you found some really, really small wires, that shouldn't burn up the wires quickly. Even if the wires are too small for the current, they wouldn't heat up quickly enough to blow up like that.

[peterg]

The machine probably doesn't draw more than 4 amps or so on 12V when it's working normally. Unless you found some really, really small wires, that shouldn't burn up the wires quickly. Even if the wires are too small for the current, they wouldn't heat up quickly enough to blow up like that.

and I checked those wires (smell test) and it wasnt them that burnt, computer shop guy reckoned it was plastic insulation on some wire in the machine (though a diode as above could be it - why I wont use 12v input until I get it checked).

and to round it off, after leaving the machine on for 3 hours to blow most of the smell out of it, I put the mask on and it was still giving a mask off warning message.. oh dear, methinks, it is stuffed after all. turns out I had the humidifier out a few mm, so I pushed it back in and all was well last night.(another thing I was doing wrong, running the machine without the humidifier properly in place) I also had the pulse oximeter on my finger with the alarm on, just in case. the O2 results were better on Intellipap auto up to 4.5cc than on the (older M Series) rental machine CPAP at 6cc. heaven.

Ill test the UPS tonight. I wonder if the 65 watt power usage in the Intellipap manual includes the humidifier (I guess it does).
because if I fall back on the UPS the humidifier will still be on as it will still think it's on mains power, whereas with the direct 12v (as per the manual) the humidifer goes off. that means, without the humidifier it would draw what - 25 watts or something. you could train a hamster on a wheel to power that much (perhaps when its cages light goes off).

[jamiswolf]

GumbyCT wrote: This is exactly why I recommend people NOT wait until they go camping or the lights go out to figure out how to hook up their equipment.

I learned that lesson while trying to connect a 110v generator to my house during a blizzard and blackout. Almost fried myself. Should have planned ahead.

I was also thinking along the lines of a fusable link...hot but not enough to burn through. Glad the machine survived.
Jamis

[Goofproof]

The smart way to build D/C powered equiptment is called a crowbar circuit. it's a inline fuse with a diode behind and across the - and + wires, when the polarity is reversed the diode causes a short and blows the fuse, saving the equiptment, costing well under a dollar, saving the equiptment. Many manufacturers don't care to do it right, it's hard to make thing completely foolproof, as fools keep evolving. Jim

After all they can always sell you a replacement.

[archangle]

Some machines may self destruct on a UPS. In particular ResMed says S8 humidifiers can't stand a MSW waveform and most UPSs put out a MSW waveform.

Most inverters that produce 120 VAC from DC also put out a MSW waveform.

[moresleep]

The smart way to build D/C powered equiptment is called a crowbar circuit. it's a inline fuse with a diode behind and across the - and + wires, when the polarity is reversed the diode causes a short and blows the fuse, saving the equiptment, costing well under a dollar, saving the equiptment. Many manufacturers don't care to do it right, it's hard to make thing completely foolproof, as fools keep evolving. Jim

After all they can always sell you a replacement.

Even smarter to wire the diode in series with the circuit, so that if power is applied the wrong way, nothing happens, and the user gets to try again...

[Goofproof]

The smart way to build D/C powered equiptment is called a crowbar circuit. it's a inline fuse with a diode behind and across the - and + wires, when the polarity is reversed the diode causes a short and blows the fuse, saving the equiptment, costing well under a dollar, saving the equiptment. Many manufacturers don't care to do it right, it's hard to make thing completely foolproof, as fools keep evolving. Jim

After all they can always sell you a replacement.

Even smarter to wire the diode in series with the circuit, so that if power is applied the wrong way, nothing happens, and the user gets to try again...

Not exactly, installing a diode in series with the circuit adds a voltage drop of over a volt to the circuit. that added resistance also heats up the diode. By putting the diode across the pos and neg little current will flow unless the power is reversed. Jim

[jmcanzo]

My Intellipap is marked on the bottom with the polarity. Center is +. I have tested mine on 12v from a portable "Jump Start" battery pack, It will run at least 9hrs on the battery (possibly longer but I woke up).. It really sounds like you reversed the polarity.

[archangle]

Not exactly, installing a diode in series with the circuit adds a voltage drop of over a volt to the circuit. that added resistance also heats up the diode. By putting the diode across the pos and neg little current will flow unless the power is reversed. Jim

The rule of thumb is 0.7V for a diode drop. If you do a blocking diode that blocks reverse voltage, you do lose 0.7V. If you want a full wave bridge circuit that will actually run with reverse voltage, you will lose around 1.4V.

On a 12V supply, you'd lose 6-12% of the total power with a diode system like this. You would waste the power and you'd have to dissipate the heat generated in the diode.

You can also use some other techniques to prevent reverse voltage damage. Those techniques have their own costs and drawbacks.

Goofproof's crowbar idea has the disadvantage of blowing a fuse, but prevents damage to the other circuitry in the machine. If it's a customer replaceable fuse, you have to deal with the problems of that.

[moresleep]

Not exactly, installing a diode in series with the circuit adds a voltage drop of over a volt to the circuit. that added resistance also heats up the diode. By putting the diode across the pos and neg little current will flow unless the power is reversed. Jim

The rule of thumb is 0.7V for a diode drop. If you do a blocking diode that blocks reverse voltage, you do lose 0.7V. If you want a full wave bridge circuit that will actually run with reverse voltage, you will lose around 1.4V.

On a 12V supply, you'd lose 6-12% of the total power with a diode system like this. You would waste the power and you'd have to dissipate the heat generated in the diode.

You can also use some other techniques to prevent reverse voltage damage. Those techniques have their own costs and drawbacks.

Goofproof's crowbar idea has the disadvantage of blowing a fuse, but prevents damage to the other circuitry in the machine. If it's a customer replaceable fuse, you have to deal with the problems of that.

Use a germanium diode, then, which has a much smaller voltage drop. Although I guess if I were dealing with a small battery pack in a camping situation, I would resent any unnecessary expenditure of juice...

[Goofproof]

Use a germanium diode, then, which has a much smaller voltage drop. Although I guess if I were dealing with a small battery pack in a camping situation, I would resent any unnecessary expenditure of juice...

A germanium diode is more meant for low power and RF circuits. They have a power drop of .2 to .3 volts. Power supply diodes are mostly Silicon with a voltage drop of .7 volts, I'll bet a germanium diode, heavy enough to carry 2 to 3 amps at 12 would would be very costly indeed, it one can be had at all.

[peterg]

Use a germanium diode, then, which has a much smaller voltage drop. Although I guess if I were dealing with a small battery pack in a camping situation, I would resent any unnecessary expenditure of juice...

A germanium diode is more meant for low power and RF circuits. They have a power drop of .2 to .3 volts. Power supply diodes are mostly Silicon with a voltage drop of .7 volts, I'll bet a germanium diode, heavy enough to carry 2 to 3 amps at 12 would would be very costly indeed, it one can be had at all.

sounds like you two know a but about electronics. the unit has power requirements to 5 amos btw.



anyhow, I had it on the Eton 700W UPS through mains last night and it didnt smoke or flame or nufin'. I'll run it off the battery only today. I wonder how much the humidifier will use over the spec 65 watts (given that the manual says to have a unit that can deliver 400w). (I also wonder/dream-on if using a microwave heater for the hudififier water would use less power - a future project perhaps).

what it did do was make a whistling wheezing noise, an air noise, that was a bit annoying, until I put the unit under the bed.
this noise was most pronounced when the humidifier was on, without the humidifier it was hardly noticable. I checked all the seals etc. maybe it was there before, but I doubt it. I reversed the hose to no avail , its coming out of the machine.

and how about when you take the humidifier off and the air is blowing out the bottom outlet (that would otherwise go into the humidifier). I dont recall it the manual or the seperate attached humidifier instructions anything about taking that rubber plug off the back of the unit (that is not used for the mask with humidifier on) and plugging up the lower outlet. it was giving mask warnings and little pressure, understandably. a tip there for newbies who don't like to experiment like me.
maybe its just more work for the DME's and experts when people blow up their machines or have air blowing out any which ways.

(pressure is auto, min 4, max 7, max effected is 4.5 for AH I3.0 with sleeping pills and some leak, and a bottle of wine). SO2 results are a lot better than the M series fixed 6cc, so its doing the job, at lower pressures and my definately happy feelings are unprecedented in my (adult) life. IOW Shit, this really works.

AND the nightly knife in the shoulder blade pains that started on 6cc months ago on the M series have diminshed the last 3 nights on the Intellipap, so I think my guess that they had something to do with the higher 6cc pressures and rib joints are likely correct.

now for the other systemic crappy joint pains.....Off topic.

heres's a question. what do you need to buy from the manufacturer to run directly off a car battery?

1. the accessory the plugs into the machine, and has a cigarette lighter plug to go into a cigarett lighter socket.
2. a unit that has alligator clamps to the battery and a cigarette lighter socket on the other end.

or both.
and does item 1 have build in safegaurds (like, duh! a fuse)
it would still be easy to put the alligator clamps on the wrong way.
Id guess both, an yes(or maybe)

I suppose I am seeking something like this repironics on for intellipap.
http://1800cpap.com/respironics-dc-powe ... r-kit.aspx
$180

1 is here
https://www.cpap.com/productpage/intell ... -cord.html
$25
but not the clips and socket part.
maybe they assume you already have a socket handy (car, jumpo starter).
the price is better and standard clip and socket units are cheap enought (but the polarity thing).

[moresleep]

Use a germanium diode, then, which has a much smaller voltage drop. Although I guess if I were dealing with a small battery pack in a camping situation, I would resent any unnecessary expenditure of juice...

A germanium diode is more meant for low power and RF circuits. They have a power drop of .2 to .3 volts. Power supply diodes are mostly Silicon with a voltage drop of .7 volts, I'll bet a germanium diode, heavy enough to carry 2 to 3 amps at 12 would would be very costly indeed, it one can be had at all.

I played around with electronics as a kid, and have this hazy recollection of using a backward biased germanium diode to keep the battery from kicking in until the AC went off, for a fairly hefty alarm system. I don't remember it being expensive. Whatever the solution, though, we know there is one; and it doesn't speak well of Intellipap that they didn't do something to make sure the machine would still work after the polarity was reversed.

For the record, my gripe is with the company "punishing" the user of the Cpap machine by allowing the machine to fail in circumstances where it might be vital to one or more nights' sleep, and where failure could easily have been designed against. I wouldn't object to the "crowbar" method so much if it just blew a fuse, and the fuse was obvious and of an easily-available variety, and could be replaced by the user without opening up the machine. But, here, it appears wires inside the machine melted, suggesting it was more than just a blown fuse, even one buried inside the machine.