Free-wheeling clamping diodes

From Frankenstein to Proteus and everything in between
Post Reply
ayard
Posts: 16
Joined: Sat Jul 10, 2021 3:19 am
Location: Williams Lake, BC, Canada

Free-wheeling clamping diodes

Post by ayard »

Hi ...

I'm new to this forum and am still getting my head around the microRusEFI and the Proteus hardware. On the Proteus, I see 4 of the low side outputs have clamping diodes installed. According to what I have read on other posts in this forum, this was intended for driving highly inductive loads such solenoids, etc. Since the fuel injectors are inductive, are these clamping diodes required or recommended for driving fuel injectors?

For a test project, I was planning to use an engine with Bosch 4.5 ohm injectors. But I see the microRusEFI doesn't have enough drive current to do this, so am now planning my first test project with the Proteus instead. I assume the Proteus should be able to drive into a 4.5 ohm injector?

Thanks,

Al
mck1117
running engine in first post
running engine in first post
Posts: 1493
Joined: Mon Jan 30, 2017 2:05 am
Location: Seattle-ish

Re: Free-wheeling clamping diodes

Post by mck1117 »

Freewheeling diodes are required when you want slow turn-off, like if you're going to PWM a solenoid (VVT, idle, etc).

Fuel injectors you specifically want to turn off quickly, which means they need active clamping instead. All outputs on proteus/microRusEfi/etc have active clamping at 40-60 volts, but only outputs with the diodes are suitable for PWM'd solenoid valves.
mck1117
running engine in first post
running engine in first post
Posts: 1493
Joined: Mon Jan 30, 2017 2:05 am
Location: Seattle-ish

Re: Free-wheeling clamping diodes

Post by mck1117 »

ayard wrote:
Mon Aug 09, 2021 1:16 am
For a test project, I was planning to use an engine with Bosch 4.5 ohm injectors. But I see the microRusEFI doesn't have enough drive current to do this, so am now planning my first test project with the Proteus instead. I assume the Proteus should be able to drive into a 4.5 ohm injector?
4.5 ohms? whaaaat? That's less than high impedance, but much more than low impedance. What are these from?
ayard
Posts: 16
Joined: Sat Jul 10, 2021 3:19 am
Location: Williams Lake, BC, Canada

Re: Free-wheeling clamping diodes

Post by ayard »

Ooops .... I was wrong, they are actually 4.6 ohms. They are a Bosch 280 150 803 and I think they are from a Porsche 944 Turbo.

Al
mck1117
running engine in first post
running engine in first post
Posts: 1493
Joined: Mon Jan 30, 2017 2:05 am
Location: Seattle-ish

Re: Free-wheeling clamping diodes

Post by mck1117 »

ayard wrote:
Mon Aug 09, 2021 3:19 pm
Ooops .... I was wrong, they are actually 4.6 ohms. They are a Bosch 280 150 803 and I think they are from a Porsche 944 Turbo.
Are you opposed to replacing them with more modern high impedance ev1 injectors? Looks like the standard Bosch geometry, so anything else should fit.
ayard
Posts: 16
Joined: Sat Jul 10, 2021 3:19 am
Location: Williams Lake, BC, Canada

Re: Free-wheeling clamping diodes

Post by ayard »

No, I'm not opposed to changing the injector, except I have the tables, etc from the old ECU and know things like the injector open delay time, etc. But I can work this out for a different injector. I don't have a dyno, so to get a rough starting point, I have recorded the injector open time for different power settings with the old ECU, then to test the new fuel tables, I can compare the injector open time at the same power settings with the new ECU. This should at least get me in the ball-park.

But if I change to another injector, it likely won't have the same flow rates, etc., so would complicate my ass-backward method I'm using now to build tables.

Also, I'm not all that familiar with the different injectors available, so would have to work out what will physically fit in the same hole. I'd prefer to not have to build new fuel rails, etc.

Al
mck1117
running engine in first post
running engine in first post
Posts: 1493
Joined: Mon Jan 30, 2017 2:05 am
Location: Seattle-ish

Re: Free-wheeling clamping diodes

Post by mck1117 »

ayard wrote:
Mon Aug 09, 2021 6:33 pm
But if I change to another injector, it likely won't have the same flow rates, etc., so would complicate my ass-backward method I'm using now to build tables.
If you're using rusEFI, it should be an easy change to switch injectors.
ayard wrote:
Mon Aug 09, 2021 6:33 pm
Also, I'm not all that familiar with the different injectors available, so would have to work out what will physically fit in the same hole. I'd prefer to not have to build new fuel rails, etc.
Pretty much all Bosch injectors fit in the same hole. Grab the injectors from literally any port-injected BMW ever made, and they'll fit. Looks like yours are 36lb/hr flow rate, which is VERY common for EV1-style injectors.
ayard
Posts: 16
Joined: Sat Jul 10, 2021 3:19 am
Location: Williams Lake, BC, Canada

Re: Free-wheeling clamping diodes

Post by ayard »

Thanks for your help .... I'm slowly getting the big picture! ;-)

I have some questions on injectors, but I'll start a new thread.

Al
mck1117
running engine in first post
running engine in first post
Posts: 1493
Joined: Mon Jan 30, 2017 2:05 am
Location: Seattle-ish

Re: Free-wheeling clamping diodes

Post by mck1117 »

After a little more research on these weird one-off Porsche injectors, I don't think they'll work with any rusEFI ECU today. They require some weird control to handle, so it's probably worth switching to newer units.
Post Reply