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The board with the silver heatsinks, converts battery voltage 13.4v to 24vdc, which feeds into the board with black heatsinks.
The board with black heat sinks is a constant current step down converter.
The plan is to have a microcontroller looking at SC boost and a few other variables (rpm, clutch position), and then selecting the current through the clutch that is most appropriate.
My thinking is to use something like 2Amps, when the supercharger is just along for the ride, and then 4 amps when it is working harder, and then 6amps during peak conditions.
The coil would overheat if I pounded it with high current all the time. These little boards seem to be up to the task, but I need to test them for an extended time with a load which can take it.
Last edited by oreo; 11-24-2019 at 01:23 PM.
Reason: formatting
So after blowing up a couple of FETs, I upgraded the heatsinks and the FETs themselves.
It is now running reliably. Keep in mind that these things are supposed to be rated at 300w and I am running less than 100w.
They are cheap though.
Should receive the rest of the parts tomorrow, so should be able to get everything built this weekend. Not sure when I will be able to test it though.
I did some boost calculations with the 2 smaller pulley sizes. Not sure that doing a 1.9" is a good idea.
After this is built I really need to do some tests to see if this concept will actually work reliably. If it does, then I can focus more on pulley sizing and actual boost levels.
FWIW, the best I ever did with the whipple was 20 PSI at 3K, 30 PSI @ 6,800. That was the 1.6L blower with 2.59:1 pulley ratio. On a ported 1.9L though.
Looking good, can't wait to see what comes of this! If you need any help with an improved MOSFET solution, let me know, I could probably throw something together that would do what you need for cheap.
FWIW, the best I ever did with the whipple was 20 PSI at 3K, 30 PSI @ 6,800. That was the 1.6L blower with 2.59:1 pulley ratio. On a ported 1.9L though.
Looking good, can't wait to see what comes of this! If you need any help with an improved MOSFET solution, let me know, I could probably throw something together that would do what you need for cheap.
Thanks Pat!
Regarding your previous setup, I was not aware you were driving the SC that hard. That equates to 19krpm @30PSi, if you rev to 7400! I doubt it was liking that.
Just need to make a washer, and I am ready to try to install this. The clutched pulley is 1.1" deeper than the standard pulley.
It will be difficult installing this, because there is not much clearance between the rad and this assembly.
I have made the supercharger pulley, however it is likely that it will need modification before it will line up correctly.
The heating was a huge problem on the old setup. First time I got 50 miles out of the blower actually spinning it to 20k without the recirc valve going through the intercooler first to cool the air down. A clutch would have been the best thing I could have done to reduce heat. If/when I build another SC setup, it will likely be clutched.
Base plate held on with 4 screws...…………………………………..……. Mid plate held on with 3 screws .....................…............................ ...................Clutch held on with 3 screws
Centering ring and shims installed ..............................……………........Pulley slid onto shaft .......................................…. Shims and Electromagnet slid onto shaft
Both the pulley and electromagnet are on bearings. There is a .025" gap between the pulley and the clutch. There is a .015" gap between the electromagnet and pulley.
When you activate the electromagnet, the clutch moves and mates up against the pulley.
The pulleys are misaligned by .060" and I need to make a washer so the bolt can hold the pulley/electromagnet on. (the hole in the shaft is threaded)
I also bored the hole too large in the electromagnet mounting plate. It's now a slip fit, and I am not sure that is going to work long term.
Even short term, my Loctite 620 is stale dated and doesn't do anything. Also the tensioner needs to be spaced further out from the engine.
Although the weather here is good, I unfortunately am not ready for any testing.
I ended up making a bearing plate for the electromagnet. It's a bit overkill, but will keep the bearing in place. I made up all the other bits I need too.
Just need to get a shorter belt, paint some stuff and then put this back together for testing.
Your a madman. Love all the fabrication, can't wait to see how it performs.
Thanks Ian. Honestly I am a little concerned that this clutch may not work reliably. No way to know for sure until it's done, but I have
some concerns for sure.
Picked up a belt today. For some reason, all my supercharger systems have ended up with some weird length belt that isn't stocked anywhere.
My go to resellers did not have this one. Napa didn't either. I special ordered it, and the wrong one arrived (correct packaging, wrong belt), which left 1pc at
the master warehouse. Fortunately they got the correct one to me today.
Testing day is fast approaching. What will it be?
1. Carnage -pulley bits coming off everywhere.
2. Disappointment -clutch not holding the required torque
3. Bliss -the thing actually working.
The car has not left the garage, but I have done some testing with mixed results.
Temporarily, I have converted my setup to supercharger only, and have connected the clutch electromagnet power supply to the rad fan 12v.
I have an on/off switch on the dash for this, so can easily engage the supercharger for testing.
This will allow me to data log the boost/rpm in a steady state, so I can understand at what point the clutch begins slipping.
Yes, the hood will close.
So after install, I measured the torque required to break the clutch loose at the supercharger pulley, and am getting lower numbers (after taking in account gearing)
than I was getting earlier. A couple of possible reasons for this.
1. I originally calculated the torque incorrectly, thinking I was going to get 35 ft/lb when the number is really 19.4 ft/lb.
2. I had to put more shims between the electromagnet and pulley and more shims between the pulley and clutch after I bolted everything together on the
car, to get everything to freewheel properly. This will reduce the clamping force.
3. Initial testing was done with the parts out of the box, which had mating surfaces which were ground fairly roughly in 1 direction. Not sure if that would improve the torque compared to a normal smooth surface.
Anyway, I ended up surface grinding the pulley, so that has a smooth finish while the clutch has the original rough surface. I need to bed these in to understand what the long term torque capability will be.
So I am now measuring 16-17 ft/lb at the supercharger pulley, which may still get me there. If not, I will need to either increase the electromagnet current further
or figure something else out.
I did run the engine up to 4000rpm, and engage the clutch to spin up the supercharger. Everything looks ok so far.
It is a little weird when the clutch is disengaged, since the engine is running and the supercharger and belt are not turning.
Just got a bunch more snow yesterday. After things are cleared, will take this out and see what happens.
Last edited by oreo; 12-15-2019 at 06:32 AM.
Reason: formatting
Ok, so testing has revealed that the clutch is good up to just shy of 15psi with 5amps electromagnet current. I wish it was more than this.
I ran quite a number of pulls, and this was pretty consistent except that on one pull it started slipping at about 13.5lbs.
It's hard to hear what is going on, because the turbo is making a lot of noise venting air and the cold weather makes the car a basket of horrible creeks and groans.
I reviewed about 25 old data logs, and the highest SC backpressure I see was 9.4psi. This pull also had the fastest boost ramp up time I saw, of 1psi/10mS.
This peak SC backpressure is very short lived. After .4S, the SC backpressure was back below 5psi (because the turbo had spooled more).
I also measured the time it takes for the electromagnet to heat up. At 5amps and 60C electromagnet internal temperature, temperature was rising 15C every minute.
Maximum electromagnet temperature is 165C.
So I can beat on this electromagnet a lot harder (higher current), for a short period of time than I am currently.
So, I think if I use a microprocessor to monitor SC boost, engine rpm and TPS I can build a system that actively changes the electromagnet current, to avoid slippage while
monitoring electromagnet temp and actual slip. Anyway, currently that is the plan. I need to understand how quickly I can ramp up the current through the electromagnet,
with the current hardware.
Oh, and the boost is a little higher than expected. When twin charged with this pulley combination, I will be running 16psi@2000rpm and 20psi@2500rpm, maybe a bit more.
Of course the biggest benefit will be more upper RPM power because I will not have the parasitic drag of the supercharger above 4500-5000 engine rpm.
Still a lot of work to do. To make this absolutely not slip and figure out if it is reliable or how to make it reliable. I have still not even run it over 4000rpm.
It's all still possible though.
Last edited by oreo; 12-15-2019 at 09:07 PM.
Reason: added electromagnet max temp
Had a bad cold last week, which lead into the flu for the weekend. Wonderful times!
only update is that my controller will do 7 amps, and ramps up current from 2-7 amps in 20ms with the electromagnet.
the clutch does not like to slip, as some of the steel from the clutch has moved over to the pulley. Too much more of that will probably reduce it's holding torque.
Next step is to ensure that 7 amps actually provides more clamping force (the thing may be saturating). Then maybe more testing.
Ok, I have learned a few things about electromagnet clutches and have decided that this clutch I have is not going to work.
Rather than going into details of what has happened over the last 4 months (basically failure after failure), I will just post the results of my testing/analysis.
First off, the benefits of making this work are considerable. For the short periods of time this setup was working, I measured the boost levels below. This equates to an engine torque improvement to 195ft/lb @2000 rpm, and 300ft/lb by 3400rpm (Virtual Dyno #’s). I would also expect to gain about 40ft/lbs of additional torque, when the supercharger is de-clutched (above 4500rpm).
Here are the issues with the current clutch:
This clutch is all steel and cannot be slipped. If you slip it, it overheats and fails. The load when switching the supercharger “on” is huge (the car lurches when doing this, and is particularly bad at higher rpm’s) and the clutch cannot dissipate this heat. Other supercharger clutches have “normal” clutch friction surfaces as well as the steel surfaces to allow for some slippage and slower engagement.
The steel cover on the electromagnet is not beefy enough. It is not capturing all of the magnetic flux and this reduces the ultimate clamping force of the clutch. I found that the electromagnet saturates at about 6.1 amps which is reasonable, but this would need to be improved.
NHV was not great. Suspending 10lbs of unsupported mass on the end of the crank is never going to be great. There was a fairly major resonance at about 2400rpm, but reasonable throughout the rest of the rpm range. I could live with it.
Reliability. Need I say more?
In addition, there would be other issues with getting this to work seamlessly.
Looking at other supercharger clutches, for example unit on the Mercedes E55, I can see that these would be better than the unit I have. I am not sure they could be made to fit.
At this point there are some things I can do to the current clutch. I purchased some friction material from McMaster Carr right at the beginning of this project. I could make a new clutch disk with this material embedded in it, as well as make a cover for the thinner parts of the electromagnet to improve it’s clamping force.
Right now, I am tired of working on this and have some other projects which have a higher probability of success, so have put this onto the back burner. I will report back if/when I have something.
11-24-2019, 01:22 PM
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