I have a medical device that requires 24V DC and runs off the mains via a transformer. I use it every night for a period of around eight hours (while sleeping) and shall have to continue to use it while on the road, sleeping in my vehicle, which could be every night.
I have a 1000-W inverter and have thought of using it to provide 220-240 volts from my second battery, then running the transformer from the inverter in order to provide 24 volts for the device. This seems like a long way round, however, and will take considerable power from the battery. What is the best way of running the device? Should I buy a less powerful inverter?

either a 12V to 240V invertor. and plug ya transformer into that.

or a 12V to 24V invertor. Maplins do em but don't know how good they are..

Or 2 batteries run in series. (you'd need to switch em to parallel to charge em.) or have some sort of change over mechanism.

What vehicle have you got?

Could you get a second 24v alternator and a couple of batteries to run it off?

Is it CPAP?

One of these 12V to 24V Step Up | eBay
would be more efficient.
just search around on the net for one that would provide enough current and a battery that can supply it for long enough.

How much power does your device need in either Watts or Amps?

Getting 24V is the easy bit, however getting 24V at 60Amps is a little bit more difficult

Medical seems to suggest high reliability and probably a very good 24V supply. You need to consider how critical it is, how long (and whether) you can operate if it fails, whether the equipment has internal batteries (and how long they will last), and what happens if it fails. You then need to balance that against how far you are going from a reliable mains supply, and how long it would take to get to one in the event of a problem.

If the answer is that reliable supply is totally critical and the loss is life threatening then I think you ought to probably contact your equipment supplier to see if they can suggest a solution - a 'home brew' is unlikely to stand up to scrutiny in the worst case scenarios.

Otherwise if the unit has internal batteries that will last longer than a worst case rescue (plus 100% safety margin) some sort of 12 - 24V DC-DC converter would probably suffice, e.g. something from someone like Alfatronix (DD Series 12-24V UP Voltage Converters, Convertisseur) but I would go and speak to them about the application and the criticality. There are converters on EBay (e.g. DC 12V to 24V 3A 72W -STEP UP- Converter Regulator Waterproof BOOST POWER Module | eBay) but I wouldn't consider EBay as source in safety critical applications.

You could also consider a 12-24V converter such as the ones above into a 2x12V battery with enough capacity to run the equipment for the expected rescue time (+100% safety margin) - I use 12V 7.2Ah batteries in UPS's (from EBay, Amazon, etc) and they are reasonably reliable, but you do need to check the current rating of the equipment against the capacity and I would also recommend a full discharge test, probably every 4-6 months, and if the discharge time is less than recover time plus about 80% then it is definitely time to think about changing the batteries.

I'm sorry if this all sounds a bit anal - and it may well be over the top - but as a Chartered Electronic Engineer with experience in Health and Safety, and also design in military applications, I am conservative in design (but not in politics!). Drop me a PM if you want any more thoughts

Bob

Oldseadog said:

How much power does your device need in either Watts or Amps?

Getting 24V is the easy bit, however getting 24V at 60Amps is a little bit more difficult

Click to expand...

On the device it says 1.25A (FG) // 3.75A (Sys). Does that make sense? I don't know what FG means. Sys. could mean "system".

My Landy's a Defender 110.

Could you get a second 24v alternator and a couple of batteries to run it off?


Two batteries in parallel in there now.

Is it CPAP?

Yes! It's the one on the left in this link.

http://www.cpap.com/cpapmachines.phpgclid=CLva6ouGtL4CFQQOwwodoRoALA

Okay so fairly critical but not as critical as full blown ventilation. Still don't want to be without it.

I would investigate a fairly resilient 24v supply then rather than a maplins/halfords/home few special lol

Btw I am nurse in ITU but in a previous job I worked in respiratory medicine