Electrical system questions

[supanova]

I have a couple of questions about the electrical system:

With the GPU off, when I start the left battery, the left and right essential buses are powered, when I would only expect the left to be powered. When starting the right battery first only the right essential bus is powered, as I would expect.

The emergency power light remains on after the batteries are on, and the emergency bus is powered.

[JGregory]

You stated you had a couple of questions, but all you did was make some statements.  Everything you described is correct behavior. If you have a specific question I would be happy to answer.

[supanova]

I'm working from the 340B documentation, which is all that I can find, but it would seem logical that operation is the same as with the A model. Feel free to correct me if I'm wrong.

Saab_340B-Electrical.pdf, 5.1 page 7, figure 2

There doesn't appear to be a connection to the left essential bus from the right battery, in the same way that the emergency bus has connections to the left and right batteries.

So, the question is, shouldn't the right essential bus not be powered unless the right battery is in the on position?

The emergency power light is documented as:

5.1, page 23/24

"Comes on if the emergency bus is not powered, or if the emergency power supply voltage drops below 24V"

As the batteries are on, and emergency bus voltage (assuming EMER on the dc amp/volt selector is emergency bus and not emergency avionic bus and power is in the green band), shouldn't the light not come on?

Edited November 10, 2018 by supanova

[JGregory]

2 minutes ago, supanova said:

So, the question is, shouldn't the right essential bus not be powered unless the right battery is in the on position?

No. When the left battery switch is on the right essential bus is powered through the bus-tie

 

3 minutes ago, supanova said:

As the batteries are on, and emergency bus voltage (assuming EMER on the dc amp/volt selector is emergency bus and not emergency avionic bus), shouldn't the light not come on?

No. The key here is that with no external power or generators to maintain the charge in the emergency battery, the emergency battery voltage will drop to below 24V.  When this happens the annunciator lights up.

[supanova]

Thanks for your reply.

But wouldn't the right battery also power the left essential bus through the bus tie if the left battery was off?

[JGregory]

11 minutes ago, supanova said:

Thanks for your reply.

But wouldn't the right battery also power the left essential bus through the bus tie if the left battery was off?

The bus-tie does not close in that scenario.

[supanova]

I didn't notice the bus tie light wasn't on during testing the right battery.

Thanks for your help. I really appreciate.