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  #11  
Old 1 Week Ago
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theksmith theksmith is offline
(Kristoffer) (K1KRS)
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Default Re: Automatic Tire Air-Up to a Pre-Set PSI
pre-requisites

my solution requires a "closed" style on-board-air system to start with (i.e. one with a pressure based shut-off).

this type of OBA setup typically includes a hard-mounted 12v compressor, a check valve, a manifold and/or air tank, an emergency blow-off valve, a pressure switch, a solenoid or heavy-duty relay, and a quick-connect fitting for the output.

here's a pretty typical example from Quadratec that uses commonly available components:




the gist of it

you pretty much just replace the typical pre-set pressure switch with a programmable one. but the devil's in the details (the settings/options)!



beyond being able to set a "turn off" pressure, you have to be able to set the hysteresis or deadband (i.e. have different turn-on and turn-off pressures).

an additional time delay feature is helpful as well, to prevent relay chatter under certain circumstances.

the module i used (QPSH-AP-42 from Automation Direct) was about $70 and also has dual outputs which came in handy.




how/why it works

if you've ever had a compressor with an integrated gauge, you've probably noticed that it's not accurate while running - they read higher than the actual PSI till you turn it off. you might have also realized it would usually be off by a consistent amount... that's the theory behind this whole idea.

for example, if you wanted your tires at around 30 PSI, you might set the turn-on at 30 and the turn-off at 40... the exact split depends on a ton of variables like hose size, tire size, compressor flow rate, etc. - so it's different for any particular system. it's pretty easy to dial in though and a 10 PSI differential seems to be a good starting point.




wiring

i'm not going to go into depth on wiring unless someone decides to actually try this and needs some assistance.

there's a wiring diagram in the instructions, just be sure you use the second one (for the AP series, if you buy the exact module i did anyway): https://cdn.automationdirect.com/sta...osense_qps.pdf

also, in that diagram, where it says "LOAD", that's where you put your heavy duty relay or solenoid coil. this module can't handle enough current to switch a compressor directly. if you need a good solenoid, this Cole Hersee 85A continuous duty one will handle most compressors. you don't need to hook the Analog Output to anything.

i wired it up with one switch to turn on the whole system, and then a 2 position switch to choose between the 2 outputs on the pressure switch. that way i can easily change from "tire mode" to a higher pressure setting for tools/lockers/etc.


continued...

Last edited by theksmith; 5 Days Ago at 11:15 AM.
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  #12  
Old 1 Week Ago
johnpa johnpa is offline
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Default Re: Automatic Tire Air-Up to a Pre-Set PSI
Do you ever get tired of being so knowledgeable and helpful.
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  #13  
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theksmith theksmith is offline
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Default Re: Automatic Tire Air-Up to a Pre-Set PSI
Originally Posted by johnpa View Post
Do you ever get tired of being so knowledgeable and helpful.������
Aimee tells me i'm "being so helpful" all the time, but she usually rolls her eyes when she says it
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theksmith theksmith is offline
(Kristoffer) (K1KRS)
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Default Re: Automatic Tire Air-Up to a Pre-Set PSI
settings

it's a good idea to configure the module before you actually make the final power hookup from the relay/solenoid to the compressor.

below is how i have mine configured, reference the instructions for more info. FYI, this is assuming you use Output #1 as your tire inflation mode and Outpt #2 as your standard air tools/lockers/etc.

in "Pro Setup Mode":
  1. sub = std
  2. dsp = 100
  3. hys = 1
  4. pos = off
  5. dpy = out1
  6. cod = 3180 / 300 (this is a read-only, it's a quick way to compare all your settings to someone else's)
  7. cpy = don't use (it will say off)
  8. aso = off
  9. rst = don't use (it will say off)
then also in "Quick Setup Mode":
  1. ot1 = hys
  2. ot2 = easy
  3. noc = 1c2c
  4. spd = 500
  5. clr = r-on
  6. unt = PSI
and finally in "Run Mode":
  1. 1-H = turn-off PSI for tire mode - example 40
  2. 1-L = turn-on PSI for tire mode (your desired PSI) - example 30
  3. 2-P = 5 to 10 PSI less than your desired PSI for tools/lockers/etc. - example 80




dialing it in

when you first try to air up a tire, the system will likely either:

- over-shoot your desired PSI and then kick off and stay off
- OR, under-shoot, i.e. kick off too soon and then keep turning on and off till it finally gets up to the right PSI

a realistic goal is within 1 to 2 PSI of your desired pressure.

- if it's overshooting, then lower your turn-off PSI a little (setting "1-H")
- if it's undershooting, then raise that same setting a bit

even though undershooting will still eventually get to your desired PSI, that kicking on & off over and over can wear out your relay/solenoid and probably isn't good for the compressor either. the delay (setting "spd") of at least 500 (half a second), prevents relay chatter at least.

the final exact setting depends on many things. i hand to dial mine in again when i changed from stock to larger tires. my current settings are actually 1-L = 29.9 and 1-H = 42.1, and it usually ends up at 30.4 to 31 the first time on each tire.

for the output 2 (tools/lockers mode) i am using the "easy" config with just a single number instead of a off & on pressure. the "spd" (delay) setting still applies here, so just be sure you go a little lower than you desired max and lower than your emergency blow-off valve! mine is currently set at 2-P = 80, which turns off pretty consistently at just under 90 PSI. my blow-off is 125 PSI.




gotchas!

2 common things that can affect the overall rate of air flow and give inconsistent results are:
  1. the voltage at the compressor... always run your rig when airing up to save the battery. even having the A/C on or off can change your idle speed and therefore the system voltage and thus the output of the compressor.

  2. if you get a kink in your air hose, or don't get a good connection with your tire chuck, you'll here the compressor start cycling on & off.
for that second issue, having a quality clip-on chuck really helps. i use a Haltec H-5265 Standard Bore Lock-On Air Chuck.




conclusion

this write-up was a little long and probably sounds way more complicated than it is! if you already have an on-board-air system, then swapping in the programmable pressure switch is easy. dialing it in can be done in 30 minutes or less.

Bradywgn71 is about to add this to his OBA setup. i'm eager to see how different the final PSI settings end up since he has a different compressor, tire size, and an air tank.
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