max battery / alternator voltage?

[dieselnutjob]

I am just wondering what the maximum voltage is that one is likely to see with a fully charged battery on a running car?

 

I am thinking that above 16V is unlikely but between 15V and 16V is probably quite common.

 

We need to do some tweaks on the diagnostic tool design, but one of the design compromises is affected by battery voltage.  There will have to be an upper limit and the processor in the tool is going to have to go on strike to protect itself above the limit.

[SiC]

A lot of app notes on this subject.

 

Here is one:

Load Dump and Cranking Protection for Automotive Backlight LED Power Supply

http://www.ti.com/lit/an/snva681a/snva681a.pdf

 

TL;DR, automotive electrical environments are hostle environments. Expect voltage peaks up to 60v - 120v from load dumps, also very low brown out voltages when cranking.

 

Stuff like 7805 aren't really suited to automotive use - even though they're very common in cheap Chinese diag tools. However there are plenty of automotive grade parts about that solve some of these problems.

 

It's all this sort of stuff that makes jump starting a bit risky to both vehicles.

 

Out of interest, what diag tool are you working on? (If you can say)

[dieselnutjob]

www.pscan.eu

[dieselnutjob]

The question relates to nominal voltage rather than spikes n things. Specifically heat dissipation in certain components which are on the 12v rail rather than 5v.

[3VOM]

This is all allegedly and I read it on the Internet but the Ford smart charging system will hit 18v if the battery is dead, hence you can not jump start cars with this product. Well you can but you can fry the electrics doing so.

[dieselnutjob]

Here is one:

Load Dump and Cranking Protection for Automotive Backlight LED Power Supply

http://www.ti.com/lit/an/snva681a/snva681a.pdf

 

 

 

It says "Normally, the output of a 12 V vehicle battery varies from 9 V to 16 V"; which is about what I would expect.  So, if a diagnostic tool refuses to work above 16V, with a suitably clear warning on the screen saying why it is refusing to work, I think that people would find that reasonable?

[SiC]

Yeah, I'd say that's reasonable. Above 15v you'll be almost certainly be boiling off the electrolyte in the battery anyway killing it.

 

Interesting product btw. I guess most of the vehicles you are targeting are effectively pre-EOBD?

[dieselnutjob]

exactly