Mi8 electronics logic questionable

[v81]

Have found a few things, and more at night about the Mi8's electrical logic that do not stack up.

Without a chart or schematic i can't be sure, but here are a few issues i'd love to find answers for.

 

The panel lighting seems to be low voltage DC powered, seems sensible and realistic.

However the lights remain (unrealisticly) dim until the main engine generators and rectifiers are bought online.

Assuming the lighting is incandescent you'd expect at least 70-80% brightness until nominal operating voltage is achieved.

Also does the APU gen not charge the batteries and supply power to the same bus these lights are on?

Switching the APU gen on does not bring the lighting up as i expect it might.

 

The most obvious issue is the R828 radio, it remains non functional until the main gens are online.

I'd expect it would come online with both inverters powered up making the radio usable for any pre-startup work required.

 

There probably are more affected systems but these 2 i encounter on a regular basis.

 

Can this be looked at, and if possible can someone point me at a bus diagram, I'd love to look at it more closely myself both as a flight sim and and electronics geek.

[Art-J]

There's some extra description and diagrams in a manual posted by AlphaOneSix:

 

It's for a different version, but maybe you'll find some clues over there.

[AlphaOneSix]

I have some basic diagrams for an Mi-8MTV-1, I'll try to get them uploaded when time permits.

[lmp]

There is an "Electrical Power Supply System Scheme" on page 142 of the manual which doesn't tell the whole story but gives some good hints. I'll be the first to admit that my understanding of electric circuits is rather basic, but here's what I've pieced together.

 

13 hours ago, v81 said:

The panel lighting seems to be low voltage DC powered, seems sensible and realistic.

However the lights remain (unrealisticly) dim until the main engine generators and rectifiers are bought online.

Assuming the lighting is incandescent you'd expect at least 70-80% brightness until nominal operating voltage is achieved.

Also does the APU gen not charge the batteries and supply power to the same bus these lights are on?

Switching the APU gen on does not bring the lighting up as i expect it might.

 

The voltage I'm seeing in the battery bus in the game is 25V with just the batteries connected, about 26.5V with the APU generator connected and 27.5V with either DC ground power or generators + rectifiers providing power. The lights seem to actually reflect this somewhat (they get a tiny bit brighter when I connect the APU generator and a whole lot brighter when I connect DC ground power or engine generators + rectifiers.

 

Are they bright enough on just batteries? Probably no, but I'm guessing that's more a problem with the cockpit lighting in the Mi-8 than the electrical simulation. The lighting was never the strong part of this module.

 

13 hours ago, v81 said:

The most obvious issue is the R828 radio, it remains non functional until the main gens are online.

I'd expect it would come online with both inverters powered up making the radio usable for any pre-startup work required.

 

The explanation here is that there are in fact two DC buses. There's the battery bus and the rectifier bus. You can think of them as the essentials and non-essentials buses respectively. The two buses are tied by a reverse current relay (which disconnects them when the battery bus voltage is greater than the rectifier bus voltage - you also get a "СЕТЬ ПИТ.ОТ АКК"  or "BATTARY IN USE" light on the main instrument panel when that happens).

 

The batteries and APU generator are connected to the battery bus via their respective switches. The APU generator can also be connected to the rectifier bus with the "Equipment test" switch. The rectifiers and DC ground power are connected to the rectifier bus - and of course since they all provide a higher voltage than the batteries do, connecting them ties the buses and charges the batteries.

 

The R-828 is connected to the rectifier bus - so in order to use it you'll need power there. If you want to use it before the engines are running, you can either connect DC ground power or use the APU generator in conjunction with the Equipment test switch. Just be aware that the generator has a rather limited power and in order to not overload it, you shouldn't connect too many systems at once.

Edited May 13, 2021 by lmp

[AlphaOneSix]

Imp basically has it all correct, but here is the relevant info from the maintenance manual (attachment).

DC Power Sources Description and Operation.pdf