In August 08 I bought my second 1.4 CVT Jazz i-DST CVT Sport 7 to replace the older one that I liked so much. I had used several accessories in the older model without any problems at all but the first time I plugged my rather old TomTom satnav into the new Jazz it failed when I started the engine.
I put that down to the age of the satnav (5 years) and thought little more of it. However, I then plugged my motorbike GPS (TomTom Rider) into the cigarette lighter socket and that, to my horror, instantly expired on starting the engine. I immediately checked the voltage at the lighter socket with the engine running and found that it was never less than 14.65 volts and switching loads in and out (lights, aircon) at one point it reached 14.8 volts. With every possible load on the system from lights etc it never drops below 14.65 volts.
I believe the alternator upper limit should be set at 14.2 +/- 0.2 volts as seems to be confirmed by my checks on another car and my BMW motorbike. Since my accessories had previously worked faultlessly on the previous Jazz, my Omega and BMW motorbike I concluded that the new Jazz is faulty in respect of the alternator voltage. I have communicated this, and the amount of my financial loss (with evidence of purchase costs) to the Honda dealer at Oxford from whom I bought the car, but they haven't even bothered to acknowledge receipt of my letter. Am I correct in thinking that the alternator is putting out too much voltage?
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Not necessarily. Some makers specify a very steep temperature coefficient of voltage with respect to temperature, so if everytrhing is very cold the voltage will be high. The regulator setting will also depend on the gassing voltage of the battery which can be quite high with calcium rich plates.
Although I deprocate this because of its effects on consumer life (lamps especially), the use of a high regulator setting allows a maker to reduce the charge time for no extra cost in alternator copper and iron. The French have been doing this for years - the Valeo machine on my partner's 106D will cheerfully manage 14.6V on a cold morning after post-heat.
A bigger alternator set to a lower voltage is a much better (and costly) solution - usually found on well engineered vehicles. My Skoda has a 120A Valeo machine with a regulator setting of 14.2V cold.
If your accessories can't take 14.8V then I'm afraid the design of them is seriously lacking. What would they do in the event of a load dump - let alone a 24V reverse jump start?
659.
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I was told many years ago never to switch my lights on until the engine had been running for about 30 seconds-reason-to allow battery and regulator to stabilize voltage.In fifty years+ of motoring,never had a bulb go.
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Most decent quality accessories that you can plug into the cigarette lighter socket are designed to cope with both 12v & 24v electrical systems. If you have a look on the plug or on the machine itself it will most likely say something like 'Input Voltage 12~24v'. Thus although it does seem mighty coincidental, I can't see why your new Jazz would have blown up both navigation systems.
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I have since checked the tech spec of the OEM TomTom adaptor lead. It is rated 12 - 24vdc so my initial conclusions that the alternator voltage is too high must be wrong.
Thanks for the info re batteries - I, too, have wondered about battery and lamp life at the higher voltage. My other car and BMW motorbike voltage with alternator on line and fully loaded sits around 13.8v - this Jazz 14.65v which, so far as I know might be the norm because have never had cause to check before this!
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Component voltage regulators, like you'll have in your sat nav, will be designed to withstand a lot higher voltage than your Jazz is putting out. Typical datasheets can specify up to 35V input.
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As said; modern alternators [well, post '94 anyway] can charge at increased voltage on cars fitted with a calcium battery. [That is why such cars MUST have calcium batteries.]
15+ volts isn't uncommon on all Fords; many Vaux and disparate models from many lands.
The DC voltage measured should not have damaged the components - now set the meter to AC and measure again....
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Was the same charger being used for both TomTom units?
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Just a thought - is the polarity of the cigarette lighter socket the right way round?
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That's a good call - you'd think it impossible but I saw it as the cause of an issue on another forum (Mercedes, I think).
I've been looking TomToms for Xmas present for daughter and the car chargers all seem to be 12-24V, so a slight excess voltage from 12V shouldn't be any sort of an issue unless the spike on start up was enormous - possible, I suppose but you'd expect other things to be failing too.
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Just a thought - is the polarity of the cigarette lighter socket the right way round?
Yes, checked that early on, thanks
Was the same charger being used for both TomTom units?
No, each has (had!) their own adaptor lead, each with a 2A mini-fuse in line, both of which blew. Because both units have been used on a variety of other vehicles it didn't occur to me until the second event that it might be the car. It seems pretty daft to think that an in-line fuse will blow fast enough to protect an electronic circuit board - I learned that lesson 20 years ago!
The DC voltage measured should not have damaged the components - now set the meter to AC and measure again....
Thanks for thought - I measure (meter AC accuracy not known) 32 volts AC engine on 1500rpm lights etc on to load the system. I have no idea if that is usual or not, never having had cause before to check!
{three separate replies all merged into one}
Edited by Dynamic Dave on 23/11/2008 at 12:45
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>>32 volts AC
If that's real, you have a problem! As your car is in warranty, ask your dealer to check the alternator output on an oscilloscope. What should be seen is a small ripple voltage, definitely less than 1 volt, what you have measured (if your measurement is true) is way beyond that.
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Many thanks - amongst other things it confirms my doubts as to accuracy of digital meter. I will get my old analogue meter (know accuracy) out of the archives and check again.
Snipquote!
Edited by Dynamic Dave on 24/11/2008 at 09:37
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As NC says, AC should be negligible; re-check and phone dealer if confirmed.
That would be an alternator output diode short-circuited and they may prefer to trailer it in.
They'd also be paying for your sat-navs.
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Thanks. You will see that I am going to check again with my old analogue meter which, according to the helpful article another referred me to, is going to be more accurate. Will let all know the results as soon as I can find the old CT471 ex-RAF test meter I have stored away somewhere.
Snipquote!
Edited by Dynamic Dave on 24/11/2008 at 09:37
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