<<Could we not mount the regulator next to the radiators somehow instead
of on the firewall. >>
Do we need to? Mine is mounted on the firewall close to the air (exit) vent.
A temperature label stuck to hte body of the regulator has read a maximum
temp. of 70C in 200 hours of service; and this was probably during heat soak
after shutdown or during a long taxiing hold, when the regulator would have
little to do.
It's agreed that mounting the regulator close to the exhaust headers
(numerous examples of this are around) gives little chance of survival..
Duncan McF.
----- Original Message -----
From: "Jan de Jong" <jan.de.jong@xs4all.nl>
Subject: Re: Europa-List: issues with Rotax 914 voltage regulator/rectifier?
>
> Very interesting material on the subject (IMO) ...
> Gilles Thse and Jrme Delamare have tested the Rotax alternator and
> the Ducati Energia rectifier/regulator and written 3 articles (with
> another to follow but that hasn't appeared):
> http://foxpapa.com/rubrique.php3?id_rubrique=138
>
> The first article (alternator) shows:
> - listing of basic properties
> - no-load: output voltage (100Vp-p max.), harmonics composition,
> effective value as a function of rpm
> - impedance at various stator currents
> - short circuit: impedance and effective current as a function of rpm
> (21A max.)
> - short circuit temperature rise (30 degrees + 17 after stopping -
> considered ok)
>
> The second article (battery) shows:
> - battery Hawker SBS8, 7.4Ah
> - discussion of battery role
> - discharged at 5A for 45 minutes
> - 40 minutes of recharging at 14.3-14.4V, current starting at 17A
>
> The third article (rectifier/regulator) shows:
> - diode bridge rectified, no load
> - diode bridge rectified with capacitor, no load
> - with shunt regulating resistor at max rpm, no load
> - with shunt regulating transistor at max rpm, no load: dissipates 260W!
> - with series regulating resistor, worst load, at max rpm
> - with series regulating transistor, worst load, at max rpm: dissipates
> 220W!
> - controlled one polarity thyristor rectification, on-off; hard on the
> hardware
> - controlled one polarity thyristor rectification, each wave; this is
> how it works
> - (JdJ: and dissipates 80W apparently - see below)
> - load budget for various conditions
>
> The fourth article would likely have reported on the marginal thermal
> situation of the regulator.
> Gilles gave a short version on the aeroelectric forum:
> - regulator dissipates max. 80W, at 240W output
> - heatsink to sea level ambient air thermal resistance is 2 degrees C/W
> (measured)
> - junction to heatsink thermal resistance is 0.3 degrees C/W (estimated)
> - junction to sea level ambient air thermal resistance is 2.3 degrees
> C/W (the sum)
> - so 80W gives a 184 degrees C increase in junction temperature above
> ambient
> - 125 degrees C is a reasonable maximum for a semiconductor junction
> - (JdJ: the maximum I have seen on a datasheet was 175 degrees)
> - so marginal is hardly the term to use
> - but moving air helps a lot - with a PC-type fan the 2.3 number changes
> to 0.8
> - so then 80W gives a 64 degrees C increase in junction temperature
> above ambient
>
> My conclusion:
> A solid state device is extremely reliable if its limits are not
> exceeded, so that is apparently what we do.
> Could we not mount the regulator next to the radiators somehow instead
> of on the firewall. That would guarantee moving air. Four meters of
> 10awg weigh 200g. The mounting should probably allow the capacitor to
> join. Can't think of further input.
> ?
>
> Jan de Jong
> 461, too slow, starting on the wings..
>
>
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