Injector Control Options

[Fred]

What do you mean by self compensate? You must always have good connections. If you don't no control strategy can help you because opening time will change away from the configured value that the software uses to generate the electrical pulsewidth.

That is another nice way to do it actually.

I just want to be clear about that diagram. The inductor IS the injector right? If so, the injectors power will come from somewhere else not in the ECU. Your diagram is probably just illustrative though, but I thought I'd clarify that.

[jharvey]

What do you mean by self compensate?

The schematic Delta put out will handle small variations of cap, ind, and resistance because it has current feedback. With the resistor approach, you will have small variations due to longer / shorter wires, good connections, and various routing variable. These variations are probably less then 1% of the expected current draw. So a 5% or 10% resistor would really be more like 6% to 11%. To prevent tolerance build up issues, it simply means you have to either bump up your default hold current, or take a measurement when you install. If you take a measurement, you can get a resistor that is as close to the the min on current as possible.

I just want to be clear about that diagram. The inductor IS the injector right?

Correct, the injector shouldn't be powered via ECU, it should be relayed to the battery.

[Fred]

I see. The hold current is fairly flexible anyway, so that doesn't matter much/at all. You have quite a large range of values between "will fall closed with less" and "will burn out with more".

Also, your design would still need some sort of snubbing/spike/fly back protection wouldn't it. I'm guessing not present in the diagram for simplicity.

[jharvey]

If you use the PIP, you would still want / need one little bleed off resistor, I still think the protected FET's are the way to go. If you don't use the protected FET's then yes snubbing is required.

[Delta]

Definitely will work - several down sides tho

you need to adjust the pulse length for different injector inductance/resistance vaules
you need to adjust the resistor for different injector values
the resistor needs to be 10W minimum and probably needs to be 15W to be safe.

I personally don't think a system once built should have to be opened and physically changed to support something simple like new injectors. Its just not good from a marketability point of view. However considering this system is aimed at people who _should_ know how to change it....perhaps thats fine.

To be honest at this point I think we should just test a few ideas and choose one and be done with it.

[Fred]

you need to adjust the pulse length for different injector inductance/resistance vaules

Isn't this the case for yours too? IE current limit *should* be adjusted per injector set? and time coefficient can/should be adjusted per injector set too? I realise that because of the current limit you can just have it too long always and limited to 4A during that period, but optimally you would tune it to be correct for your setup just the same wouldn't you?

you need to adjust the resistor for different injector values
the resistor needs to be 10W minimum and probably needs to be 15W to be safe.

OEM resistor packs from evos and other stuff are easy enough to get hold of though. And how often do people change injectors? initial set, once, twice?

I personally don't think a system once built should have to be opened and physically changed to support something simple like new injectors. Its just not good from a marketability point of view. However considering this system is aimed at people who _should_ know how to change it....perhaps thats fine.

I agree, but if you set it a bit on the long side, say 1.5ms then you won't burn them out and you will get them open. Given that they are going to be assembled they can be set "correctly" the first time during assembly anyway. But as you say, later changes will require a small rework.

There is another downside too :

double the pins on the case
double the wires to the engine bay from the case

To be honest at this point I think we should just test a few ideas and choose one and be done with it.

Agreed, Aaaabbbbbeeee??? :-)

Fred.

[Delta]

Isn't this the case for yours too? IE current limit *should* be adjusted per injector set? and time coefficient can/should be adjusted per injector set too? I realise that because of the current limit you can just have it too long always and limited to 4A during that period, but optimally you would tune it to be correct for your setup just the same wouldn't you?

Yes technically you could change it for each set, but having it peak at 4A and sit there for less than 0.5mS no matter what injector you put on it down to 0.5Ohms I think is perfectly fine. On the other hand a short simulation of the above system showed that if you adjust the timming to support 4 ohm injectors and subsequently put in 1Ohm injectors the current can spike up to 11A. Also this system does NOT take into account changes in battery voltage - mine does. But like I said, it will probably work and has its upsides. I have some high Z injectors laying around, and the parts to build most of my driver configuration...but its useless without a fuel pump, low Z injector and some form of reasonably safe liquid to squirt haha, might have to go look at the falcon wreck I've got on the lawn and pilfer some parts....

[AbeFM]

Sigh... Ok, what do I have to buy?

[Fred]

Sigh... Ok, what do I have to buy?

That's the spirit! Delta, can you help him out and sort out a simple BOM possibly cross checking that the Yankee can get them? :-) Given that he has low Z he'll be happy to test to get it included ;-)

[Delta]

I didn't include the common resistors. But this is a quick BOM.