Author Topic: A65 charging  (Read 718 times)

0 Members and 1 Guest are viewing this topic.

Ian haines

  • Star
  • *
  • Posts: 8
    • View Profile
A65 charging
« on: 05 December, 2017, 19:21:32 »
Hi all.
         Just a quick question. I took my boys bike for a shakedown run, about 25 miles. But it blood it's fuse on route, I got home and found no diode had been fitted, so got one from brit bits brilliant service and Ray  even found me a second hand heat sink to fit it to. So the question is does the charge fluctuate with the diode, as with it not connected it charges at up to 19volts but with diode in circuit it goes from 14 to 16 but could it be my digital meter or is this normal. Many thanks for your thoughts Ian




JulianS

  • Empire Star
  • *****
  • Posts: 1019
  • A10
    • View Profile
Re: A65 charging
« Reply #1 on: 05 December, 2017, 21:00:13 »
The extract from Lucas Service literature explains the zener.

It is important that the surface of the zener and the heat sink are good to allow the heat to be conducted away, and also the zener has a low torque figure to prevent damage to its brass body - only 2 - 2.3 ft/lbs. See service bulletin.

Ian haines

  • Star
  • *
  • Posts: 8
    • View Profile
Re: A65 charging
« Reply #2 on: 06 December, 2017, 10:01:38 »
Many thanks again Julian,
            I have tightened it to 2lb ft and checked a good earth, main earth goes direct to frame and heat sink plate. So will give bike another run as soon as Welsh weather brakes, with a bag of tools and spare fuse this time. Thanks again Ian
   

Caulky

  • Blue Star
  • **
  • Posts: 75
    • View Profile
Re: A65 charging
« Reply #3 on: 06 December, 2017, 11:44:14 »
You may have cooked your battery, they do not like being over-charged. (and could cause a fire)
The zener is manufactured to limit the voltage to about 15V-ish.
When the rectified Voltage from the alternator reaches the zener cut-off Voltage, It passes current (Amps) to earth.
It gets hot, hence the heat sink.
This limits the Voltage to the battery.
 
i.e. say the Voltage output (without zener) is 20V, the zener needs to reduce this Voltage by 5V.
In avalanche mode, the resistance of the diode may be very small. Say 1.0 Ohms.
W (Watts) = E squared (Volts) / R (Ohms) so, 5 x 5 = 25/1.0 = 25 Watts.
W = EI so I = W/E, I = 25W / 8V = 3 1/8 Amps.
The diode plus heatsink must dissipate 25 Watts as heat. It needs a good airflow across it to dissipate this heat.

Ian haines

  • Star
  • *
  • Posts: 8
    • View Profile
Re: A65 charging
« Reply #4 on: 08 December, 2017, 10:10:22 »
Hi caulk,
Thanks for info,checked battery all ok 12.5 v, and no loss of acid, I think the fuse blowing saved it.
We got 3 inches of snow at the moment so might be a while before I get her out to test.
            Happy Xmas everyone Ian