R22 electrical system

[baobab72]

Hi folks
I downloaded the r22 poh from the robinson website and while browsing through the system section i came across the electrical system diaghram which to say the least it looks pretty complicated!
A few questions that stem right off the bat and that hopefully the furus outthere will be able to answer:
1 Power from the battery is made available to the battery relay which has three posts - one input, one from the battery switch and one going to the starter relay - the input is self explainatory, the output to the starter as well since one of the functions of the battery is to power the starter to crank the engine up and then bring the alternator on line, while the output going to the BATT MASTER switch, does that control the ground to the relay, completing the circuit when flipping the switch to ON, what does it do exactly?
2 power from the start relay goes to the STARTER ON light, to the starter motor and then to the alternator control unit which i guess is the voltage regulator controlling the trickle charge to the electromagnetic field of the rotor of the alternator going to the F2 input on the alternator itself. The A+ output i guess is the output from the alternator to the bus. What about the ALT switch, what does it control? Because as far as i can see there is a wire going from the alternator control unti to the bus through the switch, is it the same as the A+? It looks like they are two distinguished wires! Another post is going from the starter relay to the master radio relay and from there to a number of avionics and instrumentation.
3 from the battery there is another wire going to what looks like the clutch actuator and the clock and from there to the dual tach which is also supplied from the radio master relay, is that correct?
4 are the overvoltage relay and the rectifier - i guess consisting of a number of solid state diodes - in the alternator control unit? Cos it is not shown on the schematic?
5 what are other funtions of the alternator control unit - Vr, apart from controlling the trickle charge to the rotor? Does it provide some kind of over-undervoltage or overload protection?
6 is the system single wire negative grounded, using the fuselage as a ground return to complete the circuit?

Many thanks and sorry if i have abused of your patience and willingness but i do believe that the elctrical system puzzles a lot of people outthere and i like to have a solid knowledge of the systems and not merely flipping switches while ignoring what they really do!

Baobab72

[cockney steve]

Hmmm, well, you've had no replies and I have no specific Heli knowledge, nore do I have a Robbie circuit schematic......BUT.... As a retired car-repairer, I have a fair understanding of starting and charging systems.

Sounds like your alternator is externally-regulated, so i'd guess the output comes off internal diodes. The controller is to alter what you refer to as "trickle charge"....this is the rotor-excitation current which is regulated to adjust the charge rate. possibly the alty warning-light could be battery fed,via a switch and finds it's earth through the rotor....when the output reaches battery voltage, the light goes out, as both sides are at the same potential.
the regulator unit can also be used to control the lamp.
commonly, when a starter operates, other services are disconnected to both 1, give full battery output to the starter...2, protect ancilliaries from a voltage spike that can occur when the starter-solenoid is released.

A solenoid is just an electrically operated switch a small electromagnet being used to close/open heavy current-carrying contacts....it is usual to use a spring to bias to the "normal" position (built into the solenoid) a Relay is really the same thing.

Hope this prompts someone to tell youi it's bull5h1t and give you the proper info. (is there not a workshop manual with a full description?

[Arm out the window]

Hey mate, I'm no expert but do have some knowledge gleaned over the years on various types. Standard disclaimers etc!

1. The battery relay is basically a remotely controlled switch; turning on the BATT MASTER allows current to flow through the relay's coil, causing the contacts to close and therefore now allowing current to flow from the battery to the bus bar via the ammeter, dropping in at the starter relay on the way.
Why do it this way? Basically, to allow a small current (energising the battery relay) to control a bigger current (flow from the battery), so rather than having high capacity cabling through a heavy duty battery switch, you can just have a lightweight circuit controlling a larger one, from a distance.

2. Not sure about the actual current path through the various alternator connections, but looks like the ALTERNATOR switch provides current to the control unit via the circuit breaker, so if the switch is off or the breaker pops, the alternator is disconnected from the bus bar, so although that A+ connection looks direct, it must not be active unless the control unit allows it to be.

3 The tachos are hot wired via the clutch switch so they'll keep working even if you have to turn the alternator and battery off in the event of an electrical fire or to isolate the electrics in a forced landing.

4 & 5 Not sure so I won't comment!

6 Yes, pretty sure it is.