12V Power for MS?

[GS guy]

I'm working on wiring plans for my MS install, and whole vehicle for that matter - this is a fiberglass body buggy, so total electrical system install.
My question is: does MS require a dedicated/isolated/fused (and ign. switched) +12V input directly from, the battery for a "clean" voltage input?

Right now, I'm looking at 3 main feeds coming off the battery + terminal: starter cable; adjacent to the battery a 4-terminal fuse box feeding a cooling fan and electric fuel pump (Bosch 044) relays - so only using 2 of the circuits, and a mega-fuse (175A) feeding the main chassis electrical system and American Autowire fuse panel.

What I'm planning is to come from the mega-fuse up to a buss bar at the AA fuse box location, under the dash. Off the buss bar I planned to feed the AA fuse box, MS +12V main power feed, +12V ignition coil feed, +12V boost control valve and a set of fog/driving lamps - all through separate fuses and relays.

Will these other devices coming off the buss bar affect the operation of MS, or am I just overthinking this? I was concerned with momentary V drops when say the light system and cockpit heater fan come on - screwing with having a steady +12 feeding the MS. Or is this not really an issue?
That's why I separated out the feeds to the high current draw fuel pump and main cooling fan - not wanting those, especially the fan turning on and off, to affect power input to MS.

I'm also using a ground buss bar at the fuse box to tie multiple grounds together for return to the battery, although in this case I do plan to run a dedicated ground from MS directly back to the battery.

My plan sound, or needs work?
Jeff

[kangaboy]

I don't know if i can completely answer your question, but I can give you an example of mine, and tell you how it works.

Here is my schematic:


And here is what it looks like IRL:


I don't think it matters if you ground other things to the bar, as they are all grounded by a short strap straight to the battery. For what its worth, I have everything in that pic grounded to the bar, and then a short lead straight to the neg battery terminal. The only thing that matters as far as grounding goes, is grounding all sensors to the Megasquirt.
As far as the dedicated 12v to the MS you were referring to, it does get its own fused power line, that many have hooked to a relay that is controlled by the ignition switch. My layout may answer some of you questions.

[gtmdriver]

I am using the MS relay board but I'm taking the 12v feed from the solenoid terminal which also carries the main battery cable.

As regards earthing the system it's quite critical but there's a whole section on this in the installation instructions.

http://www.msextra.com/doc/pdf/html/MS2 ... e-3.4.html

[GS guy]

Thanks for the inks and advise/photos. It doesn't look like MS is all that sensitive to minor voltage fluxuations as a parallel feed to MS, coils and fuel pump seem to be the standard configuration. I find it interesting that, depending on whose wiring diagram you look at, they indicate from no main feed power fuses, up to 80amp fuses!

I'm now leaning towards fitting a dedicated power feed from battery to a separate mega-fuse (something around 60-100A) then to a common buss fuse panel that'll feed MS +12V, +12V to the coils and +12V to boost control. I'll keep the 2nd mega fuse for dedicated chassis and main fuse panel feed, and the mini-fuse panel at the battery for cooling fan and fuel pump, and maybe add the fog-lamp power feed from here too.

I like tying in the fuel pump/coils/boost control relay activation to the main MS power feed relay - so nothing gets powered unless MS is powered on. That will be part of the wiring program.
Thanks!
Jeff

[Thorkhild]

I ran a switched 12v from the fuse panel back to my relay board, and 12v and ground straight from my battery.

I also have an extra relay triggered from the fuel pump relay from the relay board that powers my FP and Coil. So my FP and my coil are only powered if the MS is getting rpm signal.

All my grounds go to a couple of bus bars then to the battery. This setup has been working for me just fine.

[gtmdriver]

As I said in my earlier post I'm using the MS relay board. It's not cheap but it simplifies the wiring no end and provides all the relays and fuses the system needs.

[Clonebug]

I just redid my wiring up front this past winter.

I used to have a main feed from the starter post to the ignition key. From there it powered the one fuse box I had so when the key was off all power was cut to everything including the main feed to the relay box.

I now have a main feed coming from a power cutoff switch in back. I increased the wire size to 8 ga. and ran it to a distribution post up front.



You can see the dual post in the pic below. One post is power and the other is ground.
From the post it feeds the circuit box on the left for all battery power and no cutoff.
The relay gets fed from the same post and activated by the ignition switch to feed the original circuit box on the upper right that only gets power when the key is on. Nothing is fed from the ignition switch anymore. it activates the relay.



I now feed the main 12ga MS relay box wire from the continuous power box and the trigger wire is fed by the other fuse box switched on by the relay below when the key is turned on.

I seem to have better results as before I would get resets occasionally and now I don't see them in my logs any more.

I have changed my wiring so many times it is hard to keep track but I think I have it the way I want it now.
It's worked well so far but might be confusing for anyone but me.

Everything in back by the engine is pretty well triggered by ground signal and the only power I need there is for the WI pump which I pull with a fused wire from the main cutoff switch. That is the yellow fused wire you can see tied to the red main.
The two Hobbs and the solenoids work off of ground switching.

I do run a white wire back to power the coil and any switched power I would need can come from that one.

[GS guy]

Thanks again for all the ideas and advise!
I am running the relay board (and EDIS - gads! A real "old school" MS build. ) I think the RB is helpful enough to make me want to keep it, and I've already modded my MS-Extra to run boost control through the RB cable and inputting through the FIdle RB connection.
CB - after seeing your set-up (and others who posted too) it set me in a slightly different wiring approach. After sketching up a few diagrams I realized I don't really need a full +12V distribution block up near the main chassis Highway 15 fuse/relay panel, or an auxillary fuse panel down at the battery. I really just need multiple switched 12V outputs, so I just ordered up another MEGA fuse block and 60A fuse, which I'll run in parallel with the 175A feeding the HW15 fuse block. The 60A will go to a single distribution post up by the HW15 block, then branching to both constant 12V to the RB and to a high-amp relay (switched by the RB fuel pump output) which will supply the 4-circuit fuse panel. Off that I'll feed the boost controller (it grounds into the RB connection), my EDIS/coil connection, plus the fuel pump. This really simplifies the layout and provides a good starting point for where I'm going to locate all the components. Running out of room "real" fast in the confines of my buggy! I'm hoping I can pull a switched output from the HY15 to supply the RB switched input - realizing is has to stay "on" during both crank and run key positions.
Jeff

[GS guy]

Here's a rough wiring diagram DRAFT of the layout I'm planning. Looking at it now, I'm thinking of adding a 2nd relay off the power distribution lug for a dedicated fuel pump relay - also triggered by the RB FP output. That would ease the load off the one triggered relay (although most relays are rated for far higher loads).
Still working on this diagram, so at some point I'll replace it with what I end up with. I already see it's missing the FP inertial cut-off switch.



(Edited to latest diagram rev 20160629)

[gtmdriver]

This is my wiring set up.



and here it is on the car.



My main feeds to the relay board are

constant 12v+ from the solenoid/battery terminal
ignition switched 12v+ from the original ignition coil feed
Earth to one of the tinware screws on the R/H cylinder head

[GS guy]

Nice set-up GTM. Clean and tidy wiring.

I'm mounting mine to the side chassis tubes, inside the drivers side pod. Seemed like a good location, protected from the elements and one of the few locations left with a moderate amount of real estate for locating "stuff". It does, however, place it 180 degrees from the battery location, which is in the passenger side pod.

[Piledriver]

No room for it right behind the battery?
I like power and grounds as short and fat as possible.

[GS guy]

Sure looks like it from that pic! Those pics were probably taken about 2 years apart. Originally I was planning on locating the battery somewhere up front, near the front firewall, so not toooo far from the MS? That was until the radiator, fan, fuel pump, filter, hoses, brakes, steering rack/tie rods, gas tank.... and a kitchen sink(!) pretty much ate up all of that space! Then I though of getting it back by the engine, but didn't like the added heat plus more weight bias where I didn't want it, besides the total lack of room there too. This only left the side pods, and I'd already fitted the MS&RB and custom engine harness on the drivers side. Not shown is an oil cooler going in the rear of that pod with Manxter style side-pod scoop going in. "No room at the Inn" there anymore.

Passenger pod was the only space left and it allowed me to fit it towards the mid-front, again to help with the weight distribution. This goes completely against your philosophy of MS near the battery with short/fat cables Pile - so I'll have to see how it works. I'll be fitting #10ga power wire to the RB/MS, and my battery cables will be 1awg, both running back directly to the starter. I'm thinking I'll ground with a heavy braided cable from my engine block ground (MS, O2 sensor, EDIS ground point) to the starter mounting bolt and (-) battery cable. At least a "little" towards your recommendations?

Also, I'm hoping I'll have some room in that passenger pod to stash a small gear-type bag aft of the battery. That got me thinking I should probably add a couple more chassis tabs there to fit a bulkhead between battery and rest of the pod. Again, in the aft portion of the pod will be a scoop for feeding the intake air box nice cooler air, without a loud honking opening right behind the cockpit.

Man, so much more to do!
Jeff

[Clonebug]

The relay Board already has a dedicated relay for the fuel pump. It also turns the pump on and off according to engine run so you don't need an inertial switch.
The computer takes care of that.

I've been running my fuel pump through the RB FP relay without issue for 3 years so it can handle the amps going through it.

[Piledriver]

The relay Board already has a dedicated relay for the fuel pump. It also turns the pump on and off according to engine run so you don't need an inertial switch.
The computer takes care of that.

I've been running my fuel pump through the RB FP relay without issue for 3 years so it can handle the amps going through it.

Still, an impact/rollover switch has value.
You can smack things pretty hard, esp of a mid engined car, and still have the engine keep running.
A broken fuel line or coolant hose can move a lot of dangerous liquid in the 2 seconds the MS waits to shut down things.
it would be safer if it just shut down hard on a truly hard impact.
I would want the reset button on the dash tho.