Hello Colleagues

Has anyone had any experience or got any info about using small (up to say 200 v/a) inverters onboard an ambulance for powering mains driven medical devices?

Yes I know most of this type of kit has its own internal battery when there's no main supply etc, but if anyone has used these safely and successfully could yo let me know please?

Many thanks

These links are as good a place as any to start your research, Rob.

We have used several 300VA inverters for some time on the transport incubators.

We opted for the pure sine wave type as previous experience using modified sine wave units produced noise on ECG traces. In its final from, in order to simplify things for the user, we also have a box that switches automatically which means that they only have one mains lead to worry about.

I spoke with the engineers at GMAS (now NWAS) regarding the current we require and they were happy that we are staying within their limits.

Only problem we have encountered is the internal fuse blowing from time to time. This has virtually erradicated since staff were reminded to turn off the inverter when connecting and disconnecting the 12V supply.

Rob,
Quite a few ambulances have them built in these days. Have a word with your local ambulance people.
Robert

Hi Rob

Yes we've used these on our SCBU transport system it comprises of a 300w inverter that powers a 6 way IEC outlet block to power an ECG monitor, pulse ox and a few syringe drivers. This system seems to work ok and has never given us any problems, mainly I guess due to the 6 way block, as there is only the option to plug the few leads into it that we have supplied.

Inverter - Mascot 9985 300W , RS 363-5306

Hope this is of some use.
Matt.

Hello chaps, thanks for all your replies thus far.

I'm meeting with our ambulance service (GMAS) this week so the more info I've got the better. What they have told me though is that none of their current fleet have inverters fitted as standard.

Matt: your solution seems really sound. Did you have to take any special precautions about electrically earthing the inverter case? I guess you fixed it onto some sort of trolley as it's a SCBU transport system?

Cheers

Hello all,
We were hoping to equip some ambulances here with inverters but we were told they would run down the batteries and could also be a fire hazard which seems like nonsense as long as they are fitted correctly and rated for the job.

Our main reason for having the inversters was for a fluid warmer as there no battery fluid warmers which can maintain the required temp.

Hi Rob,

Been and had a look at our system, I told you wrong this morning the inverter is a 150W unit, (Mascot 9984, RS 363-5299) this unit is connected to the 12v supply sockets within the ambulance directly (we needed to extend the supplied cable), the inverter number I told you this morning connects via “screw hook” terminals this unit wasn’t used in the end as these terminals in the ambulance we use to connect directly to the incubator itself.

Regarding the system itself we have a Drager TI500 bolted to a Ferno ITU six trolley, there are a number of bonding straps between the two units, (incubator and trolley) and the inverter and distribution block are fastened to a tray under the trolley, the inverter is bolted through some existing holes in the shelf and the block is simply sat behind it.


Hope that all makes sense!!
Regards
Matt.

Hi Matt

Thanks for describing your set-up and yes it makes sense!

Noticed that the inverter you've used is a modified sine wave version. Was there a particular reason you chose this over a pure sine wave version?

Also (I'm assuming it's a 12v type??), do you know the DC current consumption of the inverter when it's on full load?

Cheers

Rob

Modified sine wave inverters tend to be used as they are generally much cheaper than their pure sine wave counterparts. However, as we found out on our monitors, can cause noise to appear on the ECG trace even with the mains filter turned on.

Here we use a 300VA inverter to power an MP30, a PrinterNOx and up to 6 Asena CC syringe drivers. With everthing on and running we are peaking just below 10 Amps.

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

Hence my question:

"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?"

D.c. connector terminations, fusing, flexibility of cables, heat-resistance/thickness of insulation, etc, etc, need to be considered carefully I reckon. As does whether earth-bonding's necessary. The inverters I've looked at are mains O/P and dc input-ground referenced.

Efficiency is quite an important issue when you're trying to give some margin for continuous operation near its limit. 1.25V O/P at 240V for a 300VA rated inverter meaning an input current of 25A off a 12V battery (assuming 100% efficiency).

Efficiency (Pout/Pin x 100%) is more likely to be nearer 80% or 90% at best I think. Hence a 12V d.c. load of ~31A at 80% with a mains load of 300VA (assuming a purely resistive load and a 240V rms sinusoidal O/P).

We limit the current drawn from the ambulance battery to 10 amps with a fuse. (equiv. to a couple of extra headlamps) This allows the inverter to power several syringe drivers and monitors etc but will not cover more power hungry requirements such as heating elements.

The 5 trolleys we have here are all fitted with the Mascot 300W sine wave inverters Robert mentioned for two years now. We limit the equipment the number of items on the output to typically run at around half load with typical current from the 12V supply being 8 to 15 Amps (the norm usually being towards the bottom end of these figures) depending on devices running and their internal battery status.

This inverter is fitted with a 40 Amp internal fuse, therefore the cable fitted to the input is rated accordingly.