Small, one-wire alternators / Megasquirt questions.

I'm going to be doing a MS conversion on my civic at some point. The OE wiring/alternator/ECU has the big charging wires, and then another half dozen or so small wires running to it. My understanding is that these smaller wires are there to let the ECU control the alternator. Some nice features like no charging at WOT, no charging when the battery is full, etc. OTOH, I'd like to simplify my harness as much as possible.

So, can MS even do that type of alternator control if I wanted to? If I don't want to, is there a small case one-wire alternator out there that is good? I know hot rodders all use the bigass GM one for their one-wire conversions, but I don't want / need one that big.

I know the small case deals are off the Mitsu cases.

Just had a thought - If I do want to stop the charging under full throttle, I could just put a relay in the charging line that is thrown when the TPS is greater than x%. That should work without getting the ECU directly involved with alternator functions, right? An alternator that isn't hooked up to a battery just free spins doesn't it?

The voltgae regulator controls the output. It may be in the ECU but most are in the alternator itself. I am not up to how these one wire units control the voltage. I would assume a built in regulator.

we used what i believe is a CS130 based GM alternator from a renix 87-90 jeep that has 1 or 2 wires plus battery, so it worked well with the XJ-R's MS. might still be bigger than you'd like but its smaller than the big cs144 alts.

iceracer wrote: The voltgae regulator controls the output. It may be in the ECU but most are in the alternator itself. I am not up to how these one wire units control the voltage. I would assume a built in regulator.

Yeah, the one-wires have an internal regulator.

In reply to DILYSI Dave:

didn't I give you a Honda FSM for your civic? if so,

Wiring Diagram, motherberkeleyer! Do you speak it?!

AngryCorvair wrote: In reply to DILYSI Dave: didn't I give you a Honda FSM for your civic? if so, Wiring Diagram, motherberkeleyer! Do you speak it?!

1. No, you did not.
2. But I do have one.
3. What the berkeley good is a stock wiring diagram when I want to rewire the engine to run with fewer wires on a different ECU motherberkeleyer!

I don't know about Hondas, but some alternators go up in smoke if not loaded due to voltage spikes blowing out the regulators. Disconnection it from the battery at 5k rpms while charging would probably be hard on the alternator and the relay. You would be switching 14 volts and probably better than 50 amps.

From what I remember of my MS days, the MS will not control an alternator. In the Miata world, this was a problem for the NB cars, as their alternator is ECU controlled. The simple solution was to just swap in an NA alternator, which is not ECU controlled.

They're not that small (but smaller than the big GM alternators), but the Bosch VW alternators have two wires, but if you put a diode between the small wire terminal and the big wire terminal, all you have to hook up is the big fat wire to the battery and it will charge just fine.

Most alternators are internally regulated. The multiple wires are FWIR signal to start the alt charging, power out from the alt (obvious big one) and a ground. I just looked at the S13 wiring diagram and there are 2 from the ign switch , 1 from the batt and one ground on the small connectors.

In reply to DILYSI Dave:

i thought you were questioning whether or not the half-dozen little wires were indeed going to / from the ECU. the stock wiring diagram would've answered that for you.

if that was not part of your question, then i take back the motherberkeleyer that i sent your way earlier.

So you want to shut the alternator OFF when you have the biggest load on the ignition and fuel system? Might be worth a little power as long as your battery can deal with it.. I guess... mine wouldn't!

I tested this back on my stock '95 Civic with an oscilloscope a while ago - it was used to test out the DIYPNP, among other things. It turns out the late '80s / early '90s Hondas have a very basic level of ECU control over the alternator. Instead of integrating a voltage regulator into the ECU, the alternator has a voltage regulator that has a signal wire connected to the ECU. If the ECU does nothing with this wire, it will charge the battery at normal voltage, around 14 volts. If the ECU grounds this wire, it drops the voltage down to 12 volts to decrease alternator drag. So you could set the MS to ground this wire at full throttle, or above a certain boost level, etc. I just didn't hook anything up to the wire and left it alone.

I just happend to be looking through the Pegasus catalog earlier and they list a small one wire 50 amp alternator for $280. A little pricey but sounds just like what you're looking for.

http://www.pegasusautoracing.com/productdetails.asp?RecID=7040

You should fab up an A/C clutch to the pulley of the alternator. Wire that up to the MAP ot TPS (or something else that will cut it off while at full throttle). That will save you the 4-5 hp that a running alternator uses.

See late-model Vettes for the actual application of this concept.

The old Dodge Omni's had a pretty handy external voltage regulator that I've used on some MS conversions.... Cheap and functional.

Festiva alternator is tiny and internally regulated. Available with v-belt or serp pulley. Three wires instead of one, though, but you wanted that anyway since one wire alternators are for morons.

You want one with 3 wires: output, idiot light/flash, and remote voltage sense. The extra wires are nothing to wire up, and you get a bulb to tell you of failure and the ability to maintain proper voltage at the fuse box or ECU itself and not whatever it ends up being after going through however many feet of wire and whatever connectors you put in line to get there.

16vCorey wrote: They're not that small (but smaller than the big GM alternators), but the Bosch VW alternators have two wires, but if you put a diode between the small wire terminal and the big wire terminal, all you have to hook up is the big fat wire to the battery and it will charge just fine.

Tell me more about this...

oldopelguy wrote: Festiva alternator is tiny and internally regulated. Available with v-belt or serp pulley. Three wires instead of one, though, but you wanted that anyway since one wire alternators are for morons. You want one with 3 wires: output, idiot light/flash, and remote voltage sense. The extra wires are nothing to wire up, and you get a bulb to tell you of failure and the ability to maintain proper voltage at the fuse box or ECU itself and not whatever it ends up being after going through however many feet of wire and whatever connectors you put in line to get there.

What he said!

Plus, even drag guys run alternators. Ignition power is important.

Except that I have no dash, no light, etc., so the light output does me nothing, and MS monitors it's voltage from the input anyway, so need for remote voltage sensing.

What I know I can do is run a big wire to the battery and a switched wire to the IG pin.

What I would like to do is run a jumper from the output post to the IG pin, and eliminate the switched connection, but depending on what I read that may or may not cause a battery drain.

DILYSI Dave wrote: Except that I have no dash, no light, etc., so the light output does me nothing, and MS monitors it's voltage from the input anyway, so need for remote voltage sensing. What I know I can do is run a big wire to the battery and a switched wire to the IG pin. What I would like to do is run a jumper from the output post to the IG pin, and eliminate the switched connection, but depending on what I read that may or may not cause a battery drain.

I am a mechanical engineer, so I don't understand any of this, but this guy says one wire alternators are death to small babies.

http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

Right. And very little of that applies to the car I'm wiring. No dash. No light. No need for remote sensing. As it's the stock alternator and I'm just wiring it differently, it is available at any autoparts store, and there is no difference in cost for the same reason.