# 12V Car Transient protection.

#### Davizuco

Joined Jul 12, 2018
20
Well, surge voltage while connecting my second battery blowed up my wireless shunt circuit.

Now I want to put a protection circuit avoiding new losses using a TVS Diode an a circuit like this:

My problem is to choose correct values:
· TVS: P6KE16A ( P6KE15A , P6KE18A ? )​
· Capacitor, 0.1uF , will 200V be enough?​
Any suggestions wil be welcome. (varistors, RL or RC ... )

Last edited:

#### crutschow

Joined Mar 14, 2008
26,998
Typically you want to put a small resistance in series with the fuse to limit the peak transient current (and voltage).
How much current does you circuit normally take?

#### Davizuco

Joined Jul 12, 2018
20
The circuit takes around 50-100ma.

It's a battery charge/discharge controller that uses Vin to measure battery output voltage.
I think the voltage drop in that resistor could be a problem, How about putting the resistor in series with the diode to protect it?, I know it won't protect the circuit then, but hope diode + capacitor will be enough.

#### ericgibbs

Joined Jan 29, 2010
12,490
hi Dav,
This PDF has info on vehicle transients, may suggest idea's.
E

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#### Davizuco

Joined Jul 12, 2018
20
Well, I was taking a look to all articles and videos I could find, (included @ericgibbs 's one, thank you).

Finally I think that using a TVS diode is the best option (newbie's opinion), If I'm not wrong, TVS are faster, and easy to find for this voltages.

Expected Vin in my van is <15V so I will go for an P6KE16A, Vbr= 15.2/16.8, lpp=27A.

I think a 10A fuse protecting the diode will be enough to filter usual van surges without burning it. I will use a second 200ma fuse just for circuit protection.

The circuit will be something like this:

Finally I prefer to have a precise voltage measurement and won't use an RC filter.