Twin Compressors

[Glenn-BJ74]

After coming back from Moab I was motivated to upgrade my air compressor capacity based on the performance I had see from the Puma and Superflow’s air compressors the Copper State Cruisers were using. Norm bought a Puma (see his Puma thread) and I bought the Superflow MV50. My plan was to mount two MV50 on their side so they would fit in the foot well behind the passenger’s seat, thereby not using any valuable cargo space, which is scare in a 74.

These compressors are wired in series on 24 volt to allow me to run two 12 volt compressors without upgrading my voltage converter which has a maximum capacity of 20 amps. They are wired from the battery with marine 8 gauge wire (closer to AWG #6 gauge) through a 40 amp marine circuit breaker (located beside the batteries) and through a 24 volt solenoid (Cole Hersee continuous duty 85 amp solenoid part #24124) through each of the compressors and back to common. I scrapped the compressor switches and internal relays. I installed a standard flip switch between the two compressors which activates the solenoid and the two compressors.

 

[Glenn-BJ74]

The compressors came with a strange thread pitch on the outlet side, which I tapped ¼” NPT to accept common air outlet fittings. I kept the coiled air hoses as they are of good quality. The two compressors are mounted on their side bolted to a piece of 21” by 13” ½” plywood, with ¾” vertical support to support the plywood floor which extends the flat cargo deck over the rear seat foot well. I have used nylock nuts where ever possible to keep things tight. The tabs are 14 gauge.

I move and tilt the passenger seat forward to access them, which can be done when I am fully loaded with camping equipment.

Most of the wiring is underneath plywood compressor mount, making for a relatively clean looking installation. I will leave the air hoses permanently connected, which will speed up the airing up process considerably. The plywood saddle is bolted to the floor using the existing seat and seat belt hardware. The right compressor will be used to air up the two right tires (hose reaches through the drivers door) and left for the two left tires, allowing me to air up two tires simultaneously. When they run together they have a cool harmonic hum.

I will do some timing checks to compared this dual compressor set-up to my existing 24v ARB compressor.

 

[bj70_guy]

Looks great Glenn, nice use of space behind the seat.
I'm fairly certain it will smoke your ARB!

 

[Glenn-BJ74]

Some Performance Numbers

With both compressors under load and the engine running the voltage at the compressor is 23.5 volts compared to 24.8 volts at the batteries, which represents a 5% voltage drop.

Time to air up one (1) 315/R16s from 15 psi to 30 psi with my existing 24 volt ARB locker compressor = 3 minutes

Time to air up two (2) 315/R16s tires simultaneously from 15 psi to 30 psi with the twin compressors set-up = 3 minutes. Equivalent of 1 1/2 min per tire.

The MV50 has about the same performance of the more expensive 24 volt ARB, although the ARB has a tank and pressure cut-off switch. Total cost installed $240, with all fittings, solenoid, circuit breaker, wood and bolts, etc.

Result is I have cut my compressor running time by 1/2 to air up four tires, eliminated the time to find, unravel and recoil my air hose and greatly extended my 24 volt ARB compressor life.

 

[Scalp]

Nice job Glenn! How many amps do they draw when both running?

 

[Glenn-BJ74]

I need to measure that somehow.

 

[canucksafari]

I need to measure that somehow.

DC amp meter is what you need. Better quality (aka more expensive) multi meters will also do DC amps.

 

[Fantom]

Most of them are limited to 10A, anything beyond that is a unit that gets used to measure stuff like alternator output (which is a lot of money). It's cheaper if you just get to know someone (or bring beers) that works in shop and has one already.
Nicely done, although I'm wondering, for all that space it's taking up in your cramped truck, wouldn't a nice York under the hood work better

 

[chet]

Nice install Glenn. Where did you get the compressors from?

 

[Glenn-BJ74]

I got them from.

Amazon.com: Q Industries MV50 SuperFlow Hi-Volume Air Compressor: Automotive

They were $140 (Can) for two. Picked up in the US. I have heard they are $49 at Costco in the US, but I looked in WA and they did not have any.

If you have the room, I would recommend the Puma.

There is very little room under the hood for a York and these units being electrical, rather than mechanical should be less maintenance in the long run. I am leaving room under the hood for my on-board-shower - a project that has been delayed until I figure out where its all going to go.