Tach Question, What does the signal look like? Options

[sgomes]

Odd question but I figure at least one of the gurus on here would know.

What does the signal look like that is sent to the tach? Is it a variable frequency pulse train? A DC voltage? A DC current? PWM?

I'm hooking up a sender for my conversion but it has multiple outputs for every conceivable type of tachometer. I just need to know what one the 914 uses.

TIA,

[Dave_Darling]

I believe that it's an exceedingly noisy square wave. Someone on here or on the Bird board checked into the signal because they weren't able to drive their tach with an MSD... Do a check on that, I think, and you may find the answer.

--DD

[TimT]

5V square wave..( for later tachs) though depends which tach....early and late VDO tachs need a different signal..

[Mueller]

Shannon, what kind of ignition are you installing??

[sgomes]

Um, actually I'm going to go with no ignition at all! (IMG:style_emoticons/default/cool_shades.gif) (I've converted it to electric.) I'm hooking up a little box that measures the motor rpm in kinda the same way the current sender measures dizzy rpm. This neat little box has a bunch of different outputs to try and cover all the bases for all the different tachs out there in the world. It also provides a rev limiter. The electric motor needs a rev limiter because they have this really neat feature of running away if you get them past a certain point. It would be the same as your gas engine taking less and less fuel the faster it went.... not pretty.

Tim... is the dividing line between "early" and "late" the same as pre '73 and post '72?

[Otmar]

Noisy square wave is correct.

aka: "variable frequency pulse train"

I drive mine with a 12V square wave ('74) and it works fine. But some (like my Vanagon) seem to want that 60V spike on the square wave that the ignition puts out. On that one the spike actually supplies the power to run the tach.

hth,

[rick 918-S]

sgomes, You and Otmar are cooool!

[sgomes]

That's very high praise comming from you!

I am not worthy. (IMG:style_emoticons/default/pray.gif) Cramming all that motor into a little teener...now THAT is cool! (IMG:style_emoticons/default/cool.gif) Me? I just had to find places for all 20 (IMG:style_emoticons/default/blink.gif) batteries! (And you guys complain about relocating just ONE to the trunk! (IMG:style_emoticons/default/laugh.gif)

Thanks for all the great answers. Looks like I've got some s'perimenting to do! (IMG:style_emoticons/default/smash.gif)

[fiid]

I think the electric conversions are hella cool.

Have any of you guys looked into doing power generation with a gnarly bike engine, or perhaps a turbocharger APU unit (mueller?) to enhance the range of the thing and be a gas-electric hybrid. If you run an APU on propane you would still be very environmentally friendly and you can exchange a propane tank at most gas stations.

Sorry for the hijacking.

[ss6]

Hey Shannon and Otmar, how about some gory details of your setups, enquiring minds want to know! How much does the car weigh after all that added lead and acid? Performance? Range? Recharge time?

So it's Zilla and CurseIt (nice one) controllers, what are you guys using for motors - storebought, tweaked, or one of a kind creations? Are you driving the wheels directly, or through the 901, etc, etc???

[sgomes]

Fiid- I know Otmar carries a generator with him. A little Honda I think. I welded a tow bar attachment to the front and extend the range by dragging it behind my truck! (IMG:style_emoticons/default/laugh.gif) Seriously though a nice propane gen set has been done by others. With all the losses added up, it's not obvious that it really is a hybrid when your done. It might be better classified as a ICE with an electric motor.

ss6- I'm glad to hear anyone on here would be even the slightest bit interested. I am planning on posting one of those epic, gorry, all-in-one posts. The transmission is at HPH getting rebuilt. It's the last part before I'm back on the road again. I'll do some photos of the installation at that point and post it all in one big lump.

In the way of a spoiler I'll answer some of your questions:

Weight: I've added about 800 pounds. (IMG:style_emoticons/default/blink.gif) They don't call 'em "lead sleds" for nothing!

Range: The absolute most I ever got before the tranny gave out (yes I'm using the 901) was a screaming 80 miles. A better average number would be around 60 miles with a mixture of city and highway miles. My commute is 30 miles per day and I've got plenty left over for around the town stuff.

Performance: It feels like a 1.7liter. Top speed is in the low 100s. I had it at 95 in fourth once. The acceleration on mine is not great since I sacrificed that for range. Talk to Otmar if you want to talk acceleration!!! (IMG:style_emoticons/default/pray.gif) He's the one with in the 13's for the quarter mile!! (IMG:style_emoticons/default/pray.gif) Of course, I kick his ass when it comes to range! (IMG:style_emoticons/default/laugh.gif) (He jokes that his range only needs to be a bit more than a quarter mile! (IMG:style_emoticons/default/smoke.gif) )

Refueling: I have an onboard charger for "opportunity" charging. That one runs off 110V so it's a bit wimpy - takes about 6-8 hours for a full charge. I can plug in at work and that pretty well negates my morning commute. (wouldn't it be great if you could refuel your gas car at work!) Off board I'm planning on a nice 220V charger that can dump ridiculous amounts of current into the batts for quick charging. I believe Otmar uses another set of batteries in his "stretch van" that can dump in a hurry so that he's ready to go for the next quarter mile run in something like 10 to 20 minutes.

Motor: I use an off the shelf Advanced DC motor. It's about 21hp. I can hear you saying, "21hp??? WTF" Electric motors are rated differently than gas engines. 21hp is the stall torque. Something that doesn't make sense for gas engines. It takes somewhere in the neighborhood of 11hp to move a 914 at 65mph. That's why EVs are so scary in the quarter mile. They've got all their horsepower at zero RPMs. Press the go pedal and just hope the tires don't shread. Otmar has two motors belted together. Once again, he was going for something different than me. The guy is a freaking mechanical/electrical genius.

Speaking of which, a Zilla is something I'd like to upgrade to someday when I'm rich. Otmar has really done a great job designing those things but right now I'm dumping my wallet into the tranny so that will have to wait.

[Otmar]

Hey Shannon,
Want to edit the title to indicate the change of subject? Just in case some one else wants to be bored with EV stuff. (IMG:style_emoticons/default/biggrin.gif)

Rick, thanks for the kudos, the Alien is pretty amazing too! (IMG:style_emoticons/default/pray.gif)

I do have a generator to charge, and a dump pack in the van, but I only use those racing. Usually I just plug it in.

Let's see, specs:
Motors: I've got two 8" Advanced DC (brand name) motors belted together. Each is rated somewhere below 20 hp, but the nice thing about electrics is that you can run them at 10X the rating for a short time. Mine probably peaks at about 220 hp now, and puts out about 1000 ft/lb of torque. Yep, that's right, 1000 ft lbs of steel twisting torque.
Needless to say, the 901 didn't last long. I run a 930 box with LSD. I'm running the motors in reverse instead of flipping the ring gear. I don't shift. 3rd gear lights them up and does over 110 so it's good enough for me. It has a 3 disc Tilton copper clutch, but I didn't hook up the release bearing and linkage. Runs 930 axles as well.
Batteries, I run 20 Exide orbitals which weigh 800 lbs total. The car comes in at 3000 lbs. Rear springs are 200lb Front torsion bars are 22mm.
Motor controller is the Zilla Z2K which I build, The biggest one of course. (IMG:style_emoticons/default/wink.gif)
Tires are Continental Eco Contact, 175-55-15. Decent traction, decent low rolling resistance. I have to get them from Switzerland since they don't sell them here. They are the stock rear tire for a Mercedes Smart car.
Performance: Best time in 1/4 mile, 13.8 sec at about 97 mph. It did 99.4 mph on a slower run. 0-60 is about 5.0 seconds, maybe a bit quicker.
Range: At least a 1/4 mile. (IMG:style_emoticons/default/biggrin.gif) Seriously, it would maybe do 30 miles if I baby it. I'd rather drive it like I stole it and go 10 miles.
Recharge: From fully empty about 1 hour. Less if it's not empty. I can plug in at a variety of charge locations around the bay area. You find some at BART, Costco, some parking lots etc.

The link on my sig line takes you to the web page I have for it. Lot's of construction pictures...
(IMG:style_emoticons/default/burnout.gif)

Have fun!

[sgomes]

Hey Shannon,
Want to edit the title to indicate the change of subject? Just in case some one else wants to be bored with EV stuff.  :D

Learning experience for the newbie.... How do I do that?

[Otmar]

Oh, now I feel stupid.
I thought I heard it could be done, but I'll be darned if I can find a way to do it. (IMG:style_emoticons/default/headbang.gif)