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By zoidberg
My battery is nearly dead, i forgot to charge it and didn't move the vehicle for a long time.
Now the voltage drops to under 9v when cranking, sometimes even lower.
This is what my tooth logger looks like.
it seems like its loosing sync twice every rotation.
Has anyone ever encountered that issue?
Is there any voltage instability issue on the 5v side of the speeduino?

I have the v 0.4 board.
theonewithin wrote:
Sun Sep 13, 2020 10:13 am
This is normal for Speeduino.
But this shouldn't be.
What is the issue here? is it the 5v source being unstable when supplied with too little input voltage?
Has anyone fixed that on their boards by now?
Or is it the arduino doing funky things when the input voltage is too low?
LPG2CV wrote:
Mon Sep 14, 2020 7:57 am
I'm not sure I would expect any car to start with a flat battery!
It will be the inconsistent cranking speed as it gets to compression causing the tooth fluctuations
The automotive standard (ISO16750) calls for operation down to 6V during cranking. Speeduino should be capable of operating reliably down to 7V at least, the regulator requires 1V of overhead and the series diode needs another 0.7V. So to answer the original question, at 9V the 5V supply should be stable.
I also expect that the issue is the varying engine speed, the trace is quite consistent.
hmmmm i will scope the 5v soon, to find out what is the case.
I had the same problem before and it only occurs on low voltage situations. the battery voltage drops to 8v when cranking when the battery is nearly empty. But the diagnostics will have to wait until i have finished my work. I will certainly keep you up to date.
Look at the toothogger.

There is no way it will start with that signal.

Where is the missing tooth?

I can't even tell what trigger wheel you are running.

If you had the Speeduino plugged in while cranking then your PC would have fed it 5V.

So it's not a issue with Speeduino. It's just not possible for it (or any ECU really) to be able to interpret the signal at all.

Depending on vehicle they may have other strategies to compensate for such a low cranking speed but in this case nothing will make it work.

Charge/replace battery. There is nothing to be fixed here.
theonewithin wrote:
Mon Sep 14, 2020 10:11 pm
Charge/replace battery. There is nothing to be fixed here.
I did exactly that and it worked again.
I think the problem really is that the engine cranks really slowly and not that coninously when the battery is low.
I charged the battery and got it running again. But i think i will have to replace it since its a bit small for the size of the motor and starter. It drops way down when the engine cranks.
Yes you are right the laptop should supply 5v.
JHolland wrote:
Mon Sep 14, 2020 9:13 am
The automotive standard (ISO16750) calls for operation down to 6V during cranking.
That's an interesting requirement. It realistically means you either must be using a switching regulator or need to run a 3v3 system (Though given most automotive sensors are 5v, that would still be challenging). I can't see any way of meeting that requirement using an LDO and reverse polarity protection unless you throw in something like a buck/boost, which brings it's own resiliency problems :?
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