Can S80 12v+ be less than 40amps?

[FrankCorrado]

Hi,

I have an S80 for quite some time and I am migrating my drivetrain to a kit car, along with the ECU of course.

I am using a totally customizable wiring kit replacing all fuses and relays. However, the kit's outputs can deliver constant 25amps each. If I need more, I have to use a relay.

The S80 wiring diagram says to use a 40amps fuse on the 12v feed. I never understood what can make the ECU use that much current.

I have "External Coil Amps" ticked in General Engine Settings and I do not use AUX5-PIN29 which can deliver 12V output. I do use the 5V output.

Do you think the ECU will ever use over 25amps current?
What would be the risk if I decide to cap it at 25amps?

tnx!

[Rob Stevens]

The 40A in the drawing also supplies all the coils and injectors, the ecu would use >0.5A

[stevieturbo]

There is no way ever the ecu would draw 40A

But bare in mind their wiring diagram also shows that same supply feeding injectors, coils etc etc

Pretty sure I've only ever had a 20A fuse on mine and even that's high. Also bare in mind, the 12v power enters the ecu via a single pin...which would never cope with a 40A load.

Coils can draw some current, injectors less so, most other actuators quite low.

Personally I prefer to have the coils on a dedicated supply, likewise injectors and other accessories. Then the ecu on another.

I've never actually monitored current draw of the DTA, but when I changed to Syvecs I was recommended to use a 1A fuse purely to offer as much protection to the ecu as possible.

I powered my lambdas from same supply so I run a 10A fuse on it.

I cant imagine why the DTA ecu would ever need more than 10A on its own either even if you were using all the 12v outputs at max current continuously.

[FrankCorrado]

Nice! I knew there was something I didn't catch on here.

I have dedicated supplies for coils (10A) and low impedance injectors (10A). I remember my other ECU before DTA was using a 1A fuse. Then I'll switch to 10A on the ECU, which means I can now feed it using an output directly from my wiring kit instead of routing a long wire from the front battery to the ECU in the back, switched on using a relay.

Tnx guys!

[mefmotorsport]

As Stevie said, ecu draws ess than 500mA, I use a 1A fuse in the ecu feed. Coils and injectors can be fed through a seperate fuse, I usually put a15A fuse in my looms for this. Injectors only take 1A each max but a coil could take up to 10A

Martin

[adamw]

In my opinion there's been a bit of misinformation posted in this thread so I'm going to add my 2 cents just for education...

Personally I prefer to have the coils on a dedicated supply, likewise injectors and other accessories. Then the ecu on another.

The ECU needs to sense true injector voltage to apply the correct dead time. It should always be powered from a common feed. Coils are generally less important but again the ECU can only apply the correct dwell time if it knows what voltage the coils are receiving. If you are using coils that are sensitive to dwell time (such as pencil coils) I would recommend the coils are also fed from the same source.

Injectors only take 1A each max

I'm not sure how mefmotorsport works this out since the OP didn't even quote what injector he is using. The S80 has 5A peak & hold drivers. Many low Z injectors will pull a peak of about 6amps, some such as the Bosch 0.5ohm can pull about 12A each.

[stevieturbo]

In my opinion there's been a bit of misinformation posted in this thread so I'm going to add my 2 cents just for education...

Personally I prefer to have the coils on a dedicated supply, likewise injectors and other accessories. Then the ecu on another.

The ECU needs to sense true injector voltage to apply the correct dead time. It should always be powered from a common feed. Coils are generally less important but again the ECU can only apply the correct dwell time if it knows what voltage the coils are receiving. If you are using coils that are sensitive to dwell time (such as pencil coils) I would recommend the coils are also fed from the same source.

Injectors only take 1A each max

I'm not sure how mefmotorsport works this out since the OP didn't even quote what injector he is using. The S80 has 5A peak & hold drivers. Many low Z injectors will pull a peak of about 6amps, some such as the Bosch 0.5ohm can pull about 12A each.

Unless you pull the ecu 12v from after the injectors on the same wire....it will never see true injector voltage. So Moot point there
The discrepancy either way is largely irrelevant though unless your wiring is terrible.
Given the minimal current draw of injectors and the ecu, volt drop in the system should be negligible. Again unless your wiring is diabolically bad.
Voltage seen at the ecu with a dedicated fused supply will still be valid.


And again I would never ever recommend anyone to wire their coil power supply from the same single wire/fuse feeding the ecu. Whether for load, fuse, protection or interference reasons, it makes no sense at all to do so

The S80 has NO peak & hold drivers. NO DTA ecu will control lowZ injectors in that fashion, and is why you must use resistors if you wish to use lowZ injectors to limit current draw.

But to say a single injector can pull 5A....I very much disagree. Especially when we are able to wire as many as 4 high impedance injectors onto a single ecu output with no worries at all. If that output is only rated at 5A and you say the injectors can pull 5A...those 4 injectors on batch fire would be pulling 20A from a 5A driver.
It just is not the case.

Even testing current years ago when playing with my new current clamp for the scope, current draw seen on my 12v line to the injectors, firing 8 injectors ( 4 pairs of 2 ), current draw really was minimal. Dont recall exact value though.

Coils were a very different story seeing as much as 22A, again as 2 coils were charging at a time due to twin/wasted spark.

Not a continuous load strictly speaking for the coils, but it's still there.

[adamw]

Unless you pull the ecu 12v from after the injectors on the same wire....it will never see true injector voltage. So Moot point there
The discrepancy either way is largely irrelevant though unless your wiring is terrible.
Given the minimal current draw of injectors and the ecu, volt drop in the system should be negligible. Again unless your wiring is diabolically bad.
Voltage seen at the ecu with a dedicated fused supply will still be valid.

Voltage drop along the injector wires is not critical since it is a constant - so it can be calculated and compensated for in your deadtime table if needed but generally it is minimal and not important. The reason it is important for the ECU to source 12V from the same relay as the injectors is nothing to do with "voltage drop", it is to avoid the usually significant voltage offsets at different locations within a car environment. These voltage offsets are never constant and change with electrical load and various other factors so they completely mess up deadtime comps. Obviously this effect is worse with large injectors/small pulsewidths so it wont bother everyone but I am just trying to point out correct practice.

And again I would never ever recommend anyone to wire their coil power supply from the same single wire/fuse feeding the ecu. Whether for load, fuse, protection or interference reasons, it makes no sense at all to do so

You should still have individual ecu/injector/ignition fuses - they just must be fed from the same relay. Noise from ignition at the ECU input should not need to be a consideration as all reputable ECU's have proper conditioning to filter this.

The S80 has NO peak & hold drivers. NO DTA ecu will control lowZ injectors in that fashion, and is why you must use resistors if you wish to use lowZ injectors to limit current draw.But to say a single injector can pull 5A....I very much disagree

Maybe I was wrong to assume the DTA drivers are P&H, maybe they are only saturated type - but whatever they are they are definitely quoted as being 5A drivers. An injector will roughly follow ohms law so I=V/R. V would normally be around 14V so that means any injector with less than 14ohms resistance will pull more than 1A. Most of the modern Bosch/Siemens/marelli Hi-Z injectors are between 9-12Ohms so will pull more than 1A.

Even testing current years ago when playing with my new current clamp for the scope, current draw seen on my 12v line to the injectors, firing 8 injectors ( 4 pairs of 2 ), current draw really was minimal.

Remember though (at least if you tested at low RPM) you probably had only one pair open at once for a very short time. At higher RPM/load, DC might reach say 80% - then you have all 4 banks pulling near full current simultaneously.

[stevieturbo]

Time open isnt really so relevant, as current draw will be pretty much the same whether open for 1ms or 10ms, and as said, DTA are quite happy to run up to 4 injectors on a single output.

Injectors simply do not draw lots of current, and testing batch fire with 8 injectors being used...could be either 2 or 4 firing at the same time. More likely 4. Either way, current draw was very low.

I'll try again when I have my engine running.

As for using a single relay for everything I can see no sensible or positive reason to do this, only negatives.

[mefmotorsport]

I based my comment on an injector being around 12 ohms and the supply being 12v hence 1 Amp. Obviously this will change depending on injector supply voltage and injector resistance but its still in the same ballpark area. In any case the current will be lower due to the duty cycle of the pulses. DTA ecu's will not drive low impedance injectors, you must use a ballast resistor so that brings the current right down again.