EBME Forums Forums Maintenance Technical Assistance Inverters for use in vehicles

Does anybody know how efficient pure sinewave invertors tend to be in comparison to modified sine wave units? What capacity (Ah) battery are you using Scottish?

The North East Ambulance Service have provided all the hospitals in the area with a transport trolley and each ambulance has been fitted with a mains supply socket. It may be worth asking them what inverters they have used.

Not looked into efficiency differences between pure and modified sine. We simple chose pure sine as modified sine was causing some issues with certain equipment.

We use the equipments own internal batteries between the department and the ambulance. Once in the ambulance the users connect the incubator, ventilator and inverter into the various 12V DC outputs. The users have a written set of instructions (written in co-operation with NWAS) giving the correct manner in which the items should be connected. This includes things like the ambulance engine must be running and the correct order in which to connect the items to prevent current surges exceeding allowed limits.

Since these instructions have been written we have, to the best of my knowledge, had no issues regarding power within the ambulances.

Thanks. Yes I'd expect harmonics superimposed on the mains output, that are conducted via mains connections into medical devices, and nasty "wideband noise" that will be conducted into and may even be radiated around devices, as an RF signal, via the connections of a modified sinewave inverter - if they're harmonics of a high enough frequency and power flux density (although manufacturers' EMC compatibility requirements probably limit this to acceptable values).

Pure sinewaves are a fundamental frequency thus no harmonics are produced in theory - a bit of an oversimplification but basic EMC theory really. Apologies for the basic applied theory. Anyhow I'd expect modified sinewave inverters to be cheaper and less complicated and more compact than sinewave inverters. We have a 300VA that fits in the palm of the hand (about half the size of a standard house brick).

Hi all

Scottish: thanks for your input mate. Any chance you could PM me with your phone number so I could ring you for a chat please?

Cheers

Emergency ambulances in North Yorkshire are all fitted with inverters and normal 13a sockets (Prosine 1000i which can deliver 10A at 240v). Have a look at www.statpower.com
Graham

Hi

Richard is that a Metric or imperial house brick?

I remember attending a meeting with GMAS a while ago where it was sugested installing solar panels on ambulance roofs as a back up as the alternators where getting close to there max power output did that idea ever see the Light of day (sorry)?
There have been concerns in the past regarding units failing and electrical safety, can they be used with RCCDs etc?
I am trying to obtain an inverter for personal use and the price differance between Pure and Modified sinewave is quite significant.

No problem Rob. Check your messages

Hello again

Thanks to everyone for their input.

We're presently speaking with NWAS about this but there is concern from them that most of the available 12v current used to power any on-board equipment is pretty much spoken for. Tales of having to leave the vehicle's engine running all the time even when parked, just to keep all the electrical/electronic systems running are quite common.

So, have purchased a Mascot 300w sine wave inverter from RS 494-5446 @ £166 for evaluation.

I'll report back as and when.

Cheers

As a PS In the past most inverters I have looked at have said that they are not for use with medical life support equipment.

300 watts/VA at mains voltage is not much but at 12 volts that is going to draw 25 amps, that needs decent wires and a good battery.
Graham mentioned the Prosime 1000i that can deliver 240v at 10A. That would draw 200A assuming 100% efficiency.That can really do damage to a battery if used for any significant time.

One of the problems with inverters is not the output but the input.

Robert