Dumb question (probably) 12v amplifier - connecting to battery.

A 12v vehcle battery is more like 13.8v when it's being charged by the alternator. It will still probely be OK, but to be sure you could put two diodes in series with the supply that will drop the voltage about

Vehicle electrics produce huge voltage spikes in some circumstances. It's u nlikely that a cheap Chinese amp has any protection against them. Its odds of survival would be improved if the leisure battery it runs from were alwa ys disconnected from the car during starting. Some cars do that.

NT

Couple of diodes and a big choke filter might help, available wildly overpriced from all good ICE emporiums :)

's unlikely that a cheap Chinese amp has any protection against them. Its o dds of survival would be improved if the leisure battery it runs from were always disconnected from the car during starting. Some cars do that.

A big choke is a great way to produce spikes fatal to silicon.

NT

Would this amp in a caravan be in use when the car engine is started or running?

Modern caravan electrics disconnect all except the caravan battery and fridge (if fitted) once the car ignition feed is live.

Chris

That would be very stupid. So you start your car as the battery is getting low, and can't use the lights to see in the caravan, watch TV, etc, etc?

I've used a lot of AV equipment that has been supplied with a 12V psu, in motorhomes, using the motorhome's 12V supply. I've never had a problem either with voltage or interference, as far as I can recall.

But do get the polarity right!

Bill

Must admit this problem with large spikes many seem to mention isn't something I've seen in practice. I've added quite a bit of home designed and built electronics to the old Rover without taking any precautions against this - just normal smoothing. And non of it has failed.

The only times I can recall high voltage spikes on a 12/24V system was on buses and milk floats around 1960. The bell coil on the bus used enough current to produce >200V spikes which destroyed the Germanium diodes in the alternator. On the milk floats, the back emf from the motors had the same effect on Germanium transistors. I've never seen a problem after 1970.

And of course cars are stuffed full of electronics these days.

I looked up the spec of a popular 20W IC audio amp designed for car use.

Suppression of Transients in an Automotive Environment 1999 by Littelfuse has a very different take on it. Independent studies by the Society of Automotive Engineers (SAE) have shown that voltage spikes from 25V to 125V can easily be generated [1], and they may last anywhere from

NT

Interesting. I've never seen a say 5v regulator that can cope with 125v.

Does the output use a bridge system, ie no common earth to speakers, if so be very careful with installing the cables and speakers. Brian

Modern control units in motorhomes/caravans isolate the supplies to things like amps* (assuming their are correctly installed) while the vehicle ignition is on. Therefore, the amp shouldn't 'see' any spikes etc on the charging supply from the vehicle.

The control units have either integral or external 'smart' chargers which, with the leisure batteries, supply a pretty clean DC supply.