clean 12v from battery?

The problem with a 12V regulator is that vehicle systems often dip below 12V (eg, cranking, switching headlights, brake lights, or wipers etc, or idling with other loads), hence the regulator drops out or delivers a lower voltage to the device.    Hence dc-dc converters are used. There are IMO great units available at Current-Logic (eg, here) though I recently heard some of their units have regulation problems, though I suspect that's for more critical applications.

oldspark wrote: The problem with a 12V regulator is that vehicle systems often dip below 12V (eg, cranking, switching headlights, brake lights, or wipers etc, or idling with other loads), hence the regulator drops out or delivers a lower voltage to the device.    Hence dc-dc converters are used. There are IMO great units available at Current-Logic (eg, here) though I recently heard some of their units have regulation problems, though I suspect that's for more critical applications.

A DC-DC converter looks perfect, the example you linked is on the larger side of what I'm looking for, both physically and in power but I get the idea. This smaller one looks alright, I could stick this in an enclosure with the relay. I might as well order one, they look quite handy even if I don't need one for this project. Thanks for the help.

Great! You found a smaller & cheaper one, though I was sure they used to have a smaller 12V cased unit for around $15.    I was blown away by their prices, hence IMO to make a robust dc-dc conv, forget it! One day I'll be getting some myself, probably even for "just in case" scenarios. They are that cheap I reckon if in doubt about a load being "12V", or "vehicle 12V" and hence 9V-16V etc and transient protected, just get a Current-Logic and play safe, and avoid dropouts to boot (pun intended - for PC etc loads). Plus those dc-dc convs are switchmode (SMPS) and hence far more efficient than linear regulators.    And apart from the one I mentioned, I haven't heard any complaints about them. In fact, quite the opposite (ie, praise.)    And BTW, not that I studied your now deleted pic in detail, but congrats on your research etc - ie, your low dropout regulator an its circuitry.

Do you have any idea of the current requirements of the DVR?

i am an idiot wrote: Do you have any idea of the current requirements of the DVR?

The power consumption of the DVR isn't in the spec but the power supply is said to supply 1A at 12V. Having used many bundled power supplies from the far east I'm dubious it will actually supply anything close to 12V at 1A. Which, isn't a problem, because obviously I wouldn't be using it on the motorcycle and second I'd be very supprised (and disappointed) if the DVR drew more than 400mA on full load.

In the real world, battery to relay switched via ignition with a 3-5 second delay would be ideal. I think you could get a 3 second delay on relay from an vehicle AC parts distributor.

That depends on what the equipment is. If it's plugpack etc supplied, it may only have an 11.5V - 12.5V tolerance. If its designed for automotive 12V, it may handle up to 15.5V or 16V etc plus typical surges, but may not like dips below 12V, 11.5V etc. Almost every vehicle's battery will drop below 11V during cranking, hence resetting dip-intolerant loads like PCs and uPC controlled equipment. However direct connection to the battery (via a relay of course) has solved many such resetting/rebooting issues, and sometimes better than a diode with big capacitor does. Certainly for PC type loads, the dc-dc converter is usually the only solution. And since DVD players incorporate uPCs, the same often applies. (Same for modern HUs etc.) (Exceptions include 5V devices like tablets & GPS. Even if they have an ancient linear regulator, they should work down to at least 8V. But most use SMPS converters ie, dc-dc converters, and hence should be dip tolerant.)

Peter, note my delay on comment. Unless m/bikes have a 2nd. non-cranking ignition.

Yeah, I did - sorry, but I did not elaborate... Although the delay means no DVD during the cranking dips & its spikes, the after-voltage might be higher than usual (some alternators output above 14.5V just after cranking if (or when) the alternator is cold), but otherwise the usual ~14.2V. The load (DVD) still sees ~20% higher voltage than is 12V rating (ie, 14.4V) even if the lower-voltage cranking dips are eliminated using a delayed relay.     Another consideration is how the unit should behave after engine stalls and hot cranking - continue operation, or is a break ok?

Point taken, I was just going for the KISS answer.