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Denso 1-wire alternator

Tfrasca

Tfrasca

Active member
Joined
Apr 20, 2015
Location
Ben Lomond, CA
So I have a 70amp Denso "mini alternator" on my 142 for packaging and simplicity.

At any RPM above idle, say 1100 and up, it will run every accessory I've got at a solid 14.5 volts. Below that, turning on some lights and other electrical loads will drop the voltage to around 13.

I know this is either because it's not exciting at the lower RPM, or it's just not making enough amperage until it spins faster. How do I determine what the issue is?
 
Once an alternator finally 'self excites' it's on until the car is turned off. So if you get 13 volts flat after a start until you rev it high enough, and then it stays 'on', it's just self exciting. If it drops down smoothly to 13V based on the RPM each time, it's just not spinning fast enough.
 
JohnMc said:
Once an alternator finally 'self excites' it's on until the car is turned off. So if you get 13 volts flat after a start until you rev it high enough, and then it stays 'on', it's just self exciting. If it drops down smoothly to 13V based on the RPM each time, it's just not spinning fast enough.
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Ah, right. It seems so obvious. It's definitely not spinning fast enough.
 
Could you not fit a 100A from a 940? I got one to fit in the 122 with a little bracket I made up. I was concerned that it might be too much for the old wiring in the car but I guess most of that is gone anyway.
 
AndrewNance said:
Could you not fit a 100A from a 940? I got one to fit in the 122 with a little bracket I made up. I was concerned that it might be too much for the old wiring in the car but I guess most of that is gone anyway.
Click to expand...

I could probably fit a 100 amp, but I was trying to stick with my weird mounting system. I tapped the block for an M12 stud in the hole where the OEM tensioner went, and that's my main pivot. It keeps the alternator really tucked into the block, and I still only have about an inch clearance to the steering idler, and 1/4" from the back of the alternator to the oil pressure sender hose.

I might have to abandon that and make a custom bracket.
 
I personally wouldn't worry about it charging at idle. That's not really a required 'use case'.
 
I'd be curious what the voltage is at those components at idle. It's possible that you have some resistance in the path between the battery and car that isn't there in the path from the alternator to the car? Those fuse blocks are fairly notorious for voltage drops after 50 - 60 years of oxidation.
 
I run a denso 80 amp volvo version on both of my 240 series and that is pretty much how they both behave. A bit low voltage like 13.5 at idle with a lot of accessories but ramps up when revved to about 14 something.

There are 14.6v setpoint regulators available. I am using the 14.4v version in both of mine. Still a good idea to make sure you don't have excessive voltage drops. I know my cars are due for a connector/fusebox cleaning again.
 
The 72A Delco I put on the PV does similar. Slight voltage drop at idle with everything off, slightest bit of a rev and it's all bright.
 
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