Z-11 Diodes and things!

[shiney]

In Z-11 architecture, there is a switched Alt Feed Battery Bus to E-Bus. Why doesn?t this feed need a diode when the feed from the Main Bus to E-Bus does? Is it because it is switched? I don't know! Also, have builders mounted their diodes on to heatsink and what diode spec have you used 12A/25A/35A/50A ?


Thanks



Shiney

[shuttle]

Hi Martin,
Hope you're well.
I'm no expert (yet) on A/C electrical systems but my understanding is as follows:

The purpose of the E-Bus is to enable extended endurance on a subset of kit at reduced current draw.
You activate the Alt Feed if there is a problem in the feed to the Main Bus and you need to switch off the Main Bus.
The diode in the Main Bus-to-E-Bus line is to ensure the Main Bus devices are isolated and not powered.

The capacity of the diode is driven by the current draw of the kit you put on your E-Bus.

Hope that's clear.

Steve H.
West Sussex.
UK

[shiney]

Hi Steve,

All is going well here, I hope you are too.

I understand the function of the e-bus etc. but based on your comments, surely the devices on the Battery Bus would also need to be isolated on the Alt feed just in the same way as those on the M-Bus are or the b-bus items insignificant for this purpose?

As always Steve, I believe you will be right, but on the face of it, it doesn’t make logical sense to me!

Any comments on heatsink?

Thanks


Martin

[shuttle]

Martin,
In Z-11 the B-Bus is always hot anyway so what electron flow would you be wanting to prevent?

In normal operation the B-Bus is connected to the rest of the circuit via the 'On' (closed) Battery Contactor.

In 'Endurance Mode' the Battery Contactor is 'Off' (open) and the E-Bus Alt Feed is 'On' (closed) so the B-Bus and E-Bus (thanks to the M-Bus-to-E-Bus diode) are the only elements being powered, and just by the battery.

Just think about what a B-Bus-to-E-Bus diode would do. It would only have any effect if the E-Bus Alt Feed and the Battery Contactor are both 'On'. But even then it only cuts off one of the two paths available for power from the Alternator to travel to the B-Bus. The path to the B-Bus via the Battery Contactor is still available. Once the Battery Contactor is 'Off', and hence the Alternator Field is off too, a B-Bus-to-E-Bus diode would not be doing anything.

Re: Heatsink, see B&C website here: http://www.bandc.biz/Diode_Installation.pdf
For B&C's diode it says to use some form of heatsink if current is more than 3Amps.

Steve

[Rick_A]

You might want to consider something other then the cheap diodes similar to the one pictured in the B&C link. This is the one that I used

http://www.periheliondesign.com/powerschottkydiodes.htm

[shuttle]

Yep, agree with Rick that the Schottky diodes drop less volts and generate less heat.