12v Televisions

[Nickhlx]

Does the Amperor unit protect against spikes?

 

 

Would a " Power Zener " clamp the spikes, and what voltage / power rating would it / they need to be to avoid being blown to bits ?

 

Presumably the Combo inverters at around £1200 have some sort of protection within else they'd be blowing regularly ( or do they ?)

 

Nick

[chris w]

Would a " Power Zener " clamp the spikes, and what voltage / power rating would it / they need to be to avoid being blown to bits ?

 

Presumably the Combo inverters at around £1200 have some sort of protection within else they'd be blowing regularly ( or do they ?)

 

Nick

clicky

 

Chris

Edited March 28, 2009 by chris w

[Nickhlx]

clicky

 

Chris

 

 

Thanks for the link - I was looking at those last night and Bi-directional ones as well - just don't have a feel for what energy these spikes may have, and was going to put a "test box" containing some "increasing voltage" samples in, in parallel and see which if any blow up - at least I will know how big the spikes were....

 

As regards to bi-directional spikes, I presume (always dangerous) that these are mainly intended for a.c. supply spikes which I guess could be either polarity. For DC I suppose an ordinary diode reverse biased would limit any reverse spikes to about a volt....

 

I will test the Unidirectional ones on the bench with a current limited PSU first, to see when they actually start conducting, after discovering the absolute max volts that the boat system reaches. Then allow a bit and select appropriate diodes accordingly.

 

Presumably it would be good to have a few and to site them close to any sensitive electronics like the TV / radio etc ?

 

Nick

[Gibbo]

Does the Amperor unit protect against spikes?

 

They say they do. I've never actually tested or inspected one to find out.

 

Gibbo

[Gibbo]

clicky

 

If it was that simple even you would be able to do this job

 

That diode starts to conduct somewhere between 11.4 and 12.6 volts (tolerance limits) so it's no use whatsoever on a 12 volt system.

 

To allow for charging voltages we'd need one that doesn't start to conduct until at least 14.8 volts. The closest one to that is the 1.5KE16A which starts to conduct somehwere between 15.2 and 16.8 volts. That has a maximum clamp voltage of 22.5 volts which is much too high to be of any use. With lower charge voltages you might get away with a 1.5KE15A which starts to conduct between 14.3 and 15.8 but that still has a clamp voltage of 21.2 volts which is still too high.

 

Gibbo

 

Would a " Power Zener " clamp the spikes, and what voltage / power rating would it / they need to be to avoid being blown to bits ?

 

No. It is an apparent solution until it's looked at in a bit more depth and with a bit more experience.

 

Presumably the Combo inverters at around £1200 have some sort of protection within else they'd be blowing regularly ( or do they ?)

 

Yes they are protected. There is a zener diode and cap from B+ to the gate of the mosfets which switches them on hard for a few hundred microseconds when the input voltage exceeds a certain limit. This basically shorts the spike out.

 

Gibbo

[Nickhlx]

If it was that simple even you would be able to do this job

 

That diode starts to conduct somewhere between 11.4 and 12.6 volts (tolerance limits) so it's no use whatsoever on a 12 volt system.

 

To allow for charging voltages we'd need one that doesn't start to conduct until at least 14.8 volts. The closest one to that is the 1.5KE16A which starts to conduct somehwere between 15.2 and 16.8 volts. That has a maximum clamp voltage of 22.5 volts which is much too high to be of any use. With lower charge voltages you might get away with a 1.5KE15A which starts to conduct between 14.3 and 15.8 but that still has a clamp voltage of 21.2 volts which is still too high.

 

Gibbo

 

 

So perhaps make up a similar circuit to the one you described above ?

 

 

 

Nick

Edited March 29, 2009 by Nickhlx

[Gibbo]

So perhaps make up a similar circuit to the one you described above ?

 

A better idea. It gets rid of the massively variable zener voltage as a result of current differences but you'd have to use a better tolerance zener.

 

Then you have the problem that for it to be really usefull it needs to be able to handle a full load dump. So reckon on maybe clamping at 16.5 volts, 100 amps for 0.5 seconds. That is a lot of energy to dissipate and requires a few mosfets to do it. I've done this on certain products in the past as it does indeed work.

 

The best solution is to simply not let the spikes get in there in the first place. It's much better, and in the long term cheaper, to design a circuit that disconnectes the input power supply when the spikes appear rather than trying to clamp them. It's more foolproof and easier to actually achieve. The circuit is a bit more complex to design.

 

The annoying part about all this for manufacturers is that all equipment designed to go on vehicles has to comply with a long, complicated, standard for spike protection. If products aren't designed to meet that standard they simply break left right and centre.

 

All equipment, that is, except the bl**dy alternator which is the one thing that causes most of the spikes in the first place. The actual culprit is exempt from the standard that itself actually makes necessary!

 

Gibbo