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[Bigron]

I did say that I expected to get flamed and I am nicely toasted now; thanks gents! 

Ron.

[Marks DTM Calib]

I did say that I expected to get flamed and I am nicely toasted now; thanks gents! 

Ron.

No intention to flame, just a case of passing on a bit of knowledge 

[Bigron]

And it was appreciated, thanks. I have worked with Schottky technology often, but never in the hostile automotive environment.
I agree that pulling the appropriate fuse would be simplest, but what are your thoughts on putting one of those 1-2 Farad capacitors so loved by the gullible teenage go-faster crowd across the leisure battery to deal with the harmful spikes?

Ron.

[Doctor Gollum]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

[Andy B]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

I'd guess lack of space under the bonnet on most cars these days would prevent you fitting one.

[Gaffers]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

I'd guess lack of space under the bonnet on most cars these days would prevent you fitting one.

Nah!  Loadsaroom!

[Kevin Wood]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

I'd guess lack of space under the bonnet on most cars these days would prevent you fitting one.

I've always wondered why caravans don't incorporate one driven by the wheels. It's self-contained then, close to the load it needs to power and the whole issue of towing electrics is completely sidestepped.

[Marks DTM Calib]

And it was appreciated, thanks. I have worked with Schottky technology often, but never in the hostile automotive environment.
I agree that pulling the appropriate fuse would be simplest, but what are your thoughts on putting one of those 1-2 Farad capacitors so loved by the gullible teenage go-faster crowd across the leisure battery to deal with the harmful spikes?

Ron.

Ineffective (in the same way they are for the audio systems!)

When I did a bit of audio design, the large capacitors work well for handling slow(er) changing fluctuations in the supply voltage but not fast transients (consider an equivalent model of a capacitor with some series resistance, L and a bloody big C and all becomes clear). To deal with faster spikes you need low capacity parts or ideally, a multitude of values......but the optimum will be dependent on the source resistance and on cars, that varies.

To protect a Schottky barrier (as they are not really a diode being a metal semiconductor interface), you need a capacitor (or two) in parallel and ideally some sort of clamp (once made a good one with a FET triggered by a Zener) so again, far from easy.

[Andy B]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

I'd guess lack of space under the bonnet on most cars these days would prevent you fitting one.

I've always wondered why caravans don't incorporate one driven by the wheels. It's self-contained then, close to the load it needs to power and the whole issue of towing electrics is completely sidestepped.

Something for you to invent & patent.    Plenty of electric driven cars on the road that you can nick a wheel off  for its motor

..... or how about like a bicycle's dynamo of old 

[Andy B]

Or fit a second alternator for the caravan. Won't suggest it again if anyone can provide a sensible reason why not.

I'd guess lack of space under the bonnet on most cars these days would prevent you fitting one.

Nah!  Loadsaroom!

That's a fair old serpentine 'fan' belt   

[YZ250]

To clarify my earlier post, the manufacturer specific tow pack on the Beemer was wired so that it sensed the caravan plug was in and disabled the 'smart' Ecu function to the alternator and switched off the stop-start function. Had no issues with the fridge or charging. On my lads Nissan it was the same, although I believe that some models require reprogramming.
On the Nissan, with the caravan on tow the voltage was a steady 14.2 and with the van unplugged the voltage varied from 12.4 to 14.8 depending on acceleration or deceleration.
So, manufacturers are aware of it and have responded to it, albeit at a price, but the after-market fitters seem to go down the ignition switched relay route to overcome the issue. 

[Doctor Gollum]

Never towed a caravan with my E Class, but it had the factory folding tow hitch Cost the original owner a few quid... Well into four figures iirc

[Sir Tigger KC]

Customer service!

I decided to phone the towbar electrics manufacturer to see if they could throw any light on the matter, in case they had something inbuilt to stop reverse drain.

Spoke to a technical bloke who said he hadn't heard of that, when I started to explain the different voltages of the two batteries he said 'Get a life' and hung up on me.

Perhaps I should

 

He must have seen this thread!   

[Marks DTM Calib]

Never towed a caravan with my E Class, but it had the factory folding tow hitch Cost the original owner a few quid... Well into four figures iirc

I saw one for the first time a few weeks ago, looking at it you wouldn't want to get the trailer nose weight to wrong!

And yes, it looked dam over complicated and expensive!

[aaronjb]

If you can't get nose weight right then you shouldn't be towing in the first place In fact, you should have your license removed (I'll stop short of suggesting a TB-like cull )