Buying & Building a Medium Ambulance into an RV – The FAM-BULANCE

[rlrenz]

Remember my system will be designed to only operate on 120 volts, so my only 12 volt loads will be a few relays, the AC blower, and the condenser fans. I figure my 12 volt load will be about 20-24 amps, which means about 4-5 amps at 120 volts into the converter. The compressor full load will be about 9 amps, so the total 120 volt load will be about 14 amps.

The Hoseline control module supplies the converter with 120 volts. Also the compressor start capacitor is sized to compensate for supply voltage variations.

 

[patoz]

That looks to be the same 12V loads mine has, and since we have the same compressors I would think those figures would be very close for both of us. The biggest difference in the two systems is on the 120V side, considering I have the seat heater, a heat strip in the blower fan, and the UV Light Air Purifier unit (1.5A), which you won't have, or maybe you will add them...

Since Hoseline normally uses a 80A converter, and I have a 55A converter, what size are you planning on using?

BTW, the description on my wiring diagram states 'PureAir Dual Voltage 12/120 AC System', so that may account for the 55A vs. 80A Converter on mine.

 

[rlrenz]

The 55 amp converter must have worked, since it came with your system. I have the same 80 amp converter that Hoseline specifies, but remember some installations (medium ambulances) can have an auxiliary condenser as well, which increases the 12 volt load. Hoseline probably planned on only loading the convrrter to 75% of rating, so it sounds about right for a maximum system.

Remember that heating can't operate whioe the system is in AC mode. I believe their largest heating coil set is rated 2.2 kW -- this requires 19.1 amps at 115 volts (which is why they normally connect the system to a 30 amp circuit). I'm not using a Hoseline heater, but a Broan wall mount 1500 watt heater. This equals 13 amps at 115 volts, which will work well on a 20 amp circuit.

 

[patoz]

Yeah, I know the heat and A/C can't operate at the same time, I was just thinking of the higher amp draw when in heat mode.

That seat is coming out of mine for sure, so I will probably remove that heater anyway, or at least make it portable with a plug-in connector. In FL I wouldn't need it but maybe a few times out of the year, so no point in having it take up space the rest of the time. I'm probably going to get a Big Buddy heater for off-grid situations also.

 

[rlrenz]

You could install a 750 watt wall heater. It would give you 2500 BTUH, which would still be more than enough.

 

[patoz]

Hahaha, 89° here today and we're talking about heaters...!

 

[SoCal Tom]

Some of the Tear Drop folks have run water from an rv water heater through a heat exchanger with a PC case fan . Uses low voltage and can provide up to 9000 btu. Could warm things up on a cold morning.
Tom


Sent from my iPad using Tapatalk

 

[patoz]

Some of the Tear Drop folks have run water from an rv water heater through a heat exchanger with a PC case fan . Uses low voltage and can provide up to 9000 btu. Could warm things up on a cold morning.
Tom


Sent from my iPad using Tapatalk

Tom, was this done using a propane water heater in an off-grid situation? Otherwise, using an electric heater with a shore power connection would be more efficient I believe.

 

[SoCal Tom]

Tom, was this done using a propane water heater in an off-grid situation? Otherwise, using an electric heater with a shore power connection would be more efficient I believe.

It was off grid. I agree, if you you have shore power a small electric heater makes it easy, but off grid it took advantage of the water heater that was already there. Here is a link to the thread [URL="http://www.tnttt.com/viewtopic.php?f=54&t=62327[/URL]

 

[rlrenz]

Air conditioner power thoughts

I've been doing some more thinking and planning for the modified Hoseline stand-by air conditioner I'm going to install. Hoseline sets the installation up on a 30 amp RV power inlet, and I'm wondering if it will live on a 20 amp circuit.

I started by determining the 120 volt load and the 12 volt load.

The 120 volt load consists of two parts - a Tecumseh rotary R134a compressor, and a 120 volt - 12 volt converter that powers the control circuitry, the ambulance air blower, and the condenser fans. The compressor is rated at 11,700 BTUH with a 9 amp current demand at 120 volts, but the converter is a little more challenging to determine:

The full load at 13.2 volts DC consists of the two condenser fans (17 amps), and the Hoseline air conditioning blower (14 amps), for a total of 21 amps (plus inrush).

The Hoseline standard converter is a PowerMax 75 amp unit. It is designed to power the condenser fans (17 amps), the control circuits, and the AC blower (14 amps), a possible secondary condenser (17 amps), plus a few smaller equipment cooling fans. When a 25% cushion is added in, the total becomes 17 amps+14 amps + 17 amps = 48 amps X 1.25 = 60 amps. Since PowerMax doesn't make a 60 amp unit, Hoseline uses the next larger converter (75 amps).

Full load for this converter is 12 amps (which explains why they can use a standard 15 amp cordset to power the converter). PowerMax states that the converter is 85% efficient, so at 13.2 volts, with a 21 amp load, the 120 volt power becomes 13.2 volts/120 volts X 21 amps/0.85 = 2.7 amps input to the converter.

This means that the total 120 volt power would be 9 amps for the compressor plus 2.7 amps for the converter = 11.7 amps. Since the converter is running at the low end of it's rating, the efficiency could conceivably be as low as 50%, which would bump the AC load up to 13.6 amps.

This is getting a little close to the 80% load point for a 20 amp breaker (16 amps), plus there is an inrush of up to 40 amps for the PowerMax converter. Additionally, there is a startup surge for the condenser fans and the AC blower.

I had planned on using a 20 amp circuit for the AC system, but now, I'm going to do as Hoseline suggests, and set the standby AC system up on a 30 amp circuit. Since the AC control box is less than 10 ft from the circuit breaker panel, the added cost for 10/3 versus 12/3 cable will be inconsequential.

Generally, any 120 volt power cables in an ambulance are type SO power cable, however I am going to use marine triplex power cable within the ambulance, and type SO for any circuit that run outside the module, such as the power to the AC compressor. Marine triplex cable has tinned, fine stranded conductors, with a smaller OD than type SO cable. All 120 volt cables are contained in convoluted tubing for added protection. I ran this by an ambulance electrician friend who agreed on triplex as a substitution for SO cable.

 

[patoz]

Bob, that is a good breakdown on the power requirement of each component, and I'm saving this for future use.

Since the IOTA unit I have is rated at 75A @12VDC output also, why do you suppose it requires a 20A cordset when the PowerMax 75A unit only requires a 15A cordset?

 

[rlrenz]

As you know, receptacle voltages in a campground or RV park can drop very low at times, which is why IOTA rates their chargers at supply voltages as low as 108 volts. The input wattage depends on amps and volts, and low voltage increases the amps. They also rate their output at line frequencies as low as 47 Hz (generator power), which reduces the charger's efficiency.

The 75 amp charger is rated at 1000 watts output at a stated efficiency of 80(+)%. With a 60 Hz, 120 volt supply, this works out to require 10.4 amps. The line cord, though, assumes a worst case scenario.

 

[patoz]

So, if I use it only at home where the AC voltage stays at a constant 119V-120V, would I be OK changing the cord set to a 15A instead of using an adapter, which I'm doing now?

 

[rlrenz]

You should be able to. Also, you won't see peak current unless you can load it down to 75 amps.

Pat, I think I have an older analog clamp on ammeter in my collection. If I do, and if I can find it, would you like to borrow it to see what your current actually is?

 

[patoz]

Bob,

I have this Fluke meter with the slot for measuring amps. That should do it, shouldn't it?

All I'm using the IOTA for right now is maintaining my two T-105 batteries, which are just sitting with no load on them.