Although fun to do, I really don't recommend doing this. The PCB seems to have voltage regulation circuitry on it, and making the modifications shown would result in excessive current and output voltage on a full 12V supply, resulting in arcing and burning of the ceramic plate and possibly transformer. This was done purely experimentally and in the modified form is only suitable for use at around 7V and in a non flammable location.
It appears that some BMW's have an ozone generator in their air conditioning system to keep it sterile. I bought one thinking it was going to be a simple module, but it turns out that it's fairly complex.
The vehicles control computer can regulate the output level via a single control wire, which can also send a signal back if the unit detects a fault. There are also three layers of control in the unit that mean that a single component failing is not likely to result in excess ozone production.
Initially I thought it might be possible to just take the control line high or pulse it manually to get a response from the unit, but it seems to require a fairly strict control signal. So I decided to bypass all the controls so the high voltage module runs all the time.
Note that bypassing all the controls also bypassed the safety monitoring and will potentially allow the unit to be run at several times its normal rating. This is not good for the ceramic ozone plate and electrodes, and could result in high voltage flashover and burning.
The unit will start creating a corona discharge (and therefore ozone) at about 6V and the current rapidly increases with voltage. I did some tests to see how hard it could be pushed and got the following results.
6V 400mA. A useful output with potentially long electrode life.
7V 840mA. This is probably close to the level it's run at by design.
8V 1A. I wouldn't recommend much higher than this.
9V 1.4A Shortened electrode life and risk of flashover.
10V 1.8A Very impressive, but too high.
11V 3A. Far too high. The voltage caused flashover on the ceramic plate resulting in sustained arcing. With normal operation the control system would probably have detected a flashover, shut the unit down and sent an error code to the ECU.
This makes me wonder if the small 100uH inductor is part of a voltage regulator to limit the output.
I'd guess the switchable transistor bias in the Royer style high voltage circuit might be to allow PWM regulation of the output.
Note that bypassing the control circuitry does remove the safety features and poses a risk of sustained tracking and burning of the unit in the vicinity of the ozone plate and the transformer.
The modifications shown were purely experimental and the unit shouldn't be used like this in an environment where failure would pose a risk.
BMW describe this unit as an ioniser and suggest that it is used to create hydrogen peroxide in the air conditioning system to sterilise it. In reality it's an ozone generator and when the spare oxygen atom of ozone (O3) contacts a water molecule (H2O) it will convert the water into hydrogen peroxide (H2O2) so it more or less works as they describe. But the highly oxidising nature of ozone will also destroy bacteria, viruses and mould directly.
There's a possibility that they're trying to avoid saying the word ozone because it is associated with health hysteria. In reality ozone exists at low levels naturally in the environment, and as long as it is kept at a low level or shielded from direct breathing it is relatively safe.
In summary, I would suggest against modifying these units the way I did. It would be much safer to control them with the correct control protocol, allowing the internal electronics to regulate the power and shut the module down in the event of failure.
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