What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Question re standby alternator

JPalese

JPalese

Well Known Member
I am considering a single bus dual alternator electrical system.

Primary alt = 60 amp

Standby = 30 amp

The standby is just along for the ride unless the primary takes the day off.

Assume the primary goes south.

Standby now on line.

What powers the plane the battery or standby alt?

The real question is do electronic items need to be load shed or does the standby alternator simply decrease the discharge rate of the battery?

Tnx
 
Last edited:
It depends on your electical load. If you are using 30 amps or less, then the battery will stay charged, the standby alternator will carry the load. If you are using more than 30 amps then either shed down to 30 or accept the battery discharging.
 
Another question

Thanks Bob - I wasn't certain if a load above the standby alternator capacity would fry the alternator or drain the battery slowly.

While there will be an avionics master switch, many of the latest avionics devices do not have their own power switch, so pulling circuit breakers is the only load shed available.

What about forcing an EFIS (or other device) to use it's backup battery for power? Will simply pulling the device CB do this?

How often and in what manner should the backup batteries be discharged and charged to keep them in good shape?
 
JPalese said:
Thanks Bob - I wasn't certain if a load above the standby alternator capacity would fry the alternator or drain the battery slowly.

While there will be an avionics master switch, many of the latest avionics devices do not have their own power switch, so pulling circuit breakers is the only load shed available.

What about forcing an EFIS (or other device) to use it's backup battery for power? Will simply pulling the device CB do this?

How often and in what manner should the backup batteries be discharged and charged to keep them in good shape?
Click to expand...
The alternator will only out out its rated power, so if you're pulling more an that, you'll discharge the battery.

In my experience, depending on the panel, the avionics will pull a total of 10-20 amps, with momentarily a couple of extra amps when transmitting on the radio. The alternator field will draw a few amps. 5 amps for a 60-70 amp alt normally. The best quick load shed is kits and pitot heat if able. I wouldn't pull breakers unless you see your voltage dropping. Kill lights first then think about avionics. Many avionics can be killed by a switch on the unit as well, but that depends on what you have.

I'd only go to backup battery if the secondary alt fails. An EFIS will usually draw a couple of amps max under normal circumstances.

In my experience, most items with backup batteries recommend that you test the life at annual condition inspection. If under a certain length of time, they recommend replacing. I don't think most of them have memory like the Ni-Cads of old, so regular full discharge isn't necessary.
 
Back up alternator

Hi Jesse

On this note, which Back Up alternator would you recommend??

The B&C with 20 Amps and an external regulator or a Plane Power with 30 Amps and internally regulated??

The Plane Power should be easier to install I guess..

Thank you

Bruno
[email protected]
 
Back Up Alternator

Hi Greg

Thanks for the info

I've got a Plane Power 60 Amps Main Alternator right now and as I'm planning to fly my -4 IFR eventually I wanna have some back up if the main one ever quits on me.

I'm leaning toward the Plane Power model so far due mostly to ease of installation with its internal regulator but I could be swayed toward the B&C SD-20 if it is Superior..

Thanks again

Bruno
 
Nowhere close

Plane (pun intended) ignorance here: I assume on piston engines both the main and B/U alternators are hard mounts (always spinning, no clutch type mechanism?). Why not just use 2 regular alternators, are they just that more heavy than the backups? Are there not enough mounting points? Price point? I just don't understand (lack of knowledge, no judgement).
 
I recently went through all of the alternator options as I'm planning for future configurations. I looked at the Plane Power with the internal regulator and auto alternators with external regulators. The Plane Power unit seems like the simplest solution and it does provide the overvoltage protection. The external regulator configuration is not much more complicated though. A "Ford" type regulator is available for around $20 and it is very simple to wire. These regulators can be used with the B&C alternators. The B&C alternators are reasonably priced but their regulators are expensive. I think the 20A backup unit is a good choice. You need to buy there overvoltage protection module for $36 to protect that alternator too.

By the way an auto alternator with external regulator and overvoltage protection is about $300 cheaper than the Plane Power unit.
 
LAMPSguy said:
Plane (pun intended) ignorance here: I assume on piston engines both the main and B/U alternators are hard mounts (always spinning, no clutch type mechanism?). Why not just use 2 regular alternators, are they just that more heavy than the backups? Are there not enough mounting points? Price point? I just don't understand (lack of knowledge, no judgement).
Click to expand...

Mounting locations, primarily. The B&C backup alternators (and some others) will mount on the vacuum pad on the back of the engine. With modern avionics there are plenty of ways to build an airplane that doesn't need to suck :rolleyes: so you can free up the vacuum drive pad.
 
airguy said:
Mounting locations, primarily. The B&C backup alternators (and some others) will mount on the vacuum pad on the back of the engine. With modern avionics there are plenty of ways to build an airplane that doesn't need to suck :rolleyes: so you can free up the vacuum drive pad.
Click to expand...

Nevertheless, both the B&C SD20 and SD8 are spinning any time the engine is running, as the previous poster surmised. It means you have to keep all wiring, hoses, bundles, etc clear of them.
 
Rupester said:
Nevertheless, both the B&C SD20 and SD8 are spinning any time the engine is running, as the previous poster surmised. It means you have to keep all wiring, hoses, bundles, etc clear of them.
Click to expand...

True - but the SD20 has only internal spinning parts, no worries about external contact there. The SD8 has an external housing that rotates and could be contacted by wiring/hoses.
 
A little OT but does anyone have any idea if there is much of a load on the engine with the B/U alternator just spinning w/o being used as primary?

Thinking in terms of HP used.


Glenn Wilkinson
 
Hp consideration

Hi Glen

I asked that exact question to DIck (Plane Power ) and he said it might be as little as 1 or 2 Hp max so nothing to be too concern about I would say

Bruno
 
glenn654 said:
A little OT but does anyone have any idea if there is much of a load on the engine with the B/U alternator just spinning w/o being used as primary? Thinking in terms of HP used. Glenn Wilkinson
Click to expand...

Virtually nil without an electrical load, you are just spinning the shaft in bearings. The rule of thumb is about 1 horsepower for each 12 amps of output when loaded.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
SD-20

Well I finally decided on the B&C SD-20 with their external regulator.

Their special Oshkosh price and the guarranty that it will fit with their oil filter adapter installed swayed me toward them.

Now all I need to figure out is how to wire the thing...:eek:

Wish me luck

Bruno
[email protected]
 
Last edited:
Main & Std By Alternator Wiring

Hello Gents

Well I started installing my new SD-20 Back Up alternator and also review my previous installation of my Main alternator and I hit a wall..

I'm not sure 100 % on how to wire the B leads of both alternator.

1.- Main alternator...

If I used Bob Nuckoll's AeroElectric book, in there he suggest ( if I understood correctly) to wire the main alternator B lead directly to the starter main power terminal ( Page 7-13, fig 7-12 ) via either a current limiter or a CB.So this way ,it shorten the large conductor from the alternator B-lead to the bus bar and has some other advantages..

My question is : Is it a good way to wire my main alternator and am I better off using a C/B rather then a current limiter.

2.- Back Up alternator.

So far I have install the voltage regulator and some of the wires but I'll like to know how I should terminate the wire from the B lead once I wire it to a C/B?? Do I actually need a C/B or is a current limiter good enough..I think it might be easier to control the alternator via a C/B:confused:

Where do I go from there??

Do I go from the C/B to the bus bar or to the alternator shunt??

This is where I hit the wall, I'm just not sure what to do next and I don't want fry anything..:eek:

Both Alternator field are wired thru their respective C/B..

Any suggestions are welcome

Thanks

Bruno
[email protected]
 
Hi Bruno-

I don't have my Aeroelectric book in front of me, but thinking through the logic of connecting the Alternator B lead to the starter main power terminal, this would work if you did not have a firewall mounted starter contactor as Vans shows in their plans. I suppose Bob was thinking this might be a good idea in a configuration where the starter contactor is on the starter itself. Some people wire this way, but most use the Vans recommended firewall mounted starter contactor. Think about it, if you had a starter contactor on the firewall, your alternator would only be supplying juice when the starter contactor is closed. That would not work too well!

On your 2nd question, CB vs current limiter is a matter of personal choice. Personally, I prefer current limiters. You will never intentionally open this circuit breaker (it is not a switch) since you always control the function of your alternator by opening and closing the field circuit, which is already a breaker as you mentioned, so that is fine. The CB or current limiter on the B-lead is to protect the B-lead (and the rest of your electrical system) from a dead short. On the other side of the current limiter or the CB you go to the main bus (most people wire directly to the main bus contactor - the side that becomes energized when the main bus switch is closed). If you have an essential bus you may wire instead to the essential bus rather than the main bus - depends on your architecture goals really.

Do you have any local builders or A&Ps that can inspect your wiring before powering everything up? That might be a good idea and could help you from "frying anything"!

Hope this helps...
 
Last edited:
Alternator Wiring

Hi Noah

Thanks a lot for the info, it is greatly appreciated.

Reference connecting the B lead of my Main alternator to the starter main power terminal, mine is mounted on the firewall same as Vans.

It is power as long as I have power on the aircraft.The way it is wired right now is like this.

The battery is connected to one stud of the battery contactor and on the other side of the Battery contactor, there is a wire that goes to the starter main power terminal (this where the cable from the Alt B lead is connected ) and on the other side of the starter main power terminal there is a cable ( # 6 ) that go from there to the alternator shunt.

So when I turn the master switch ''ON'', power flows thru the battery contactor to the starter contactor and from there to the starter..

I don't know if it is wired correctly but it does work, I just wanna make sure it is safe the way it is...

Regarding the current limiter, should I mount it between the Alternator B lead and the starter main power terminal ?

Ref the Back up ALT : Tried to install it today on my -4 but it doesn't work..

There is an interference between the ALT and the B&C o?l filter adapter..

I contacted B&C ( Superb service BTW ) and they are working on a solution that will work with an RV-4..I might have to use a special spacer for the vacuum pump drive like the one use on the RV-10..

I'll keep everyone posted on the results since I'm the first to do this on a -4 apparently.

Thanks again Noah

Bruno
 
Bruno,
You are NOT better off using a circuit breaker. For one thing, it is not desired to run a heavy wire through the firewall to the instrument panel to where a circuit breaker would be mounted. Another reason not to use a circuit breaker is that they have moving parts that can fail. A circuit breaker can nuisance trip. An ANL current limiter will only blow when the alternator or associated wiring shorts out. I suggest that you wire it according to Bob Nuckolls diagrams. His circuits have been perfected and proven over time.
There has been some discussion on the AeroElectric list about using a MIDI fuse (which does not cost as much) instead of an ANL.
See http://www.matronics.com/forums/viewtopic.php?p=405736&sid=1fbb4a358d91bc8667acf5645e6f6642
and
http://forums.matronics.com/viewtopic.php?p=391840&sid=f8f02046c66810cc18bb1782e2726292
Joe Gores
 
Current Limiter

Hi Joe

The more I think about it, the more I'm gonna use a current limiter.Until I read Bob's book, I had never heard of a current limiter..Nice little gadget.

I will carry at least one of each in the aircraft just in case one blows while on the road.

That is what I will use on my Main and Std By Alt ( If I'm able to install it ).

What size of ANL would you guys install on a 60 AMPS Alternator?? A 80 Amps or more ??

I've got a 40 AMPS ANL that came with the SD-20 so this one should be good.

I think I should mount them between the B Lead and the Buss Bar(same as a breaker) Am I right on this??

They're also easier to install..

I'll keep you guys posted on the results.

Thanks again

Bruno
[email protected]
 
Last edited:
Bruno,
According to Bob Nuckolls' diagram, a 60 amp ANL should be used with a 60 amp alternator. There is no need to carry extra current limiters. If one blows, there is a major problem, like a shorted wire or alternator.
The ANL current limiters should be connected to the load side of the main battery contactor, not necessarily right next to the contactor but at either end of the heavy wire (on the engine side of the firewall) that connects to the load side of the main battery contactor. The ANL current limiters should NOT be connected to the main power bus that is located under the instrument panel. It is not desired to run another heavy wire through the instrument panel.
The purpose of the ANL current limiter is NOT to limit the alternator current because the alternator is self limiting. The purpose of the ANL is to limit battery current when there is a short circuit in either the alternator or its wiring.
Joe Gores
 
Stand By Alternator question

Hi All

I just finished the installation of my Back Up alternator today ( B&C SD-20) and once completed I did a run up to test the installation and everything appears to be working fine except for the light provided by B&C that turns ON and will flash if the alternator's load is too high.

On the back of switch ( Light ) there are two wires already soldered on and they are marked as 1 and 2 but there are no indication to know if one is power and the other one ground or whatever they are??

Anyone knows exactly what they are and exactly how to wire that switch/light??

Thank you for your help.

Bruno
[email protected]
 
The installation documentation states that this is a midged flange 330 bulb. If this is the case, it is an incandescent bulb and therefore it doesn't matter which wire goes where.

Simply wire one lead to the 2A sense breaker/fuse and the other to the controller terminal 5 as depicted on the B&C wiring diagram.
 
Switch/light wiring

Hi Kurt

That is the way I wired it but will check again..

I did check the light prior so it should be fine

Thanks

Bruno
 
You've probably already done this, but I'll try anyway.

In order for the standby alternator to go active, the system voltage needs to drop below what your primary alternator provides. Have you removed the primary alternator from the charging system by pulling the field breaker or disconnecting the b-lead, and then starting the engine?

The yellow light won't light up until the standby alternator goes active.
 
SWITCH/LIGHT

Hi Kurt

Yes I did that by pulling the CB of the main Alternator field and checking on the Ampmeter that the stand by is pulling the load but I just don't get a light ''ON''

i'll check again first chance I get..

Thanks

Bruno
 
Switch/light

Well I rewired the switch as per the instructions and got the light to work when press to test but it still doesn't come on when the Std-By Alt takes the load ???

I have an ampmeter & a voltmeter on the a/c so I can see when the std by takes over but the light still doesn't do a thing..

Anything I may have forget,,,anyone ???

Thanks

Bruno:confused:
 
The standard B&C light shipped with the standby alternator kits is not a press-to-test type. That leads me to believe you are using a different light?

Is it possibly an LED light that you have?
 
Light

Hi kurt

I'm using the light that came from B&C and wired it as per the instruction but it doesn 't matter what I do,it doesn't come on when the SD-20 takes over

Here's how I wired it

One wire from the light goes to the 2 Amp C/B and the other wire goes to pin 5 on the voltage regulator

Pin 3 from the regulator goes to the same c/b basically completing the circuit

I don't know what else to try except trying another C/B ???

Thank you for your suggestion so far,it helps checking things over

Bruno
 
Last edited:
Bruno,
Remove the wire from terminal 5 on the voltage regulator and ground that end of the wire. Turn on the master switch. The lamp should illuminate. If it does, the above test proves that the circuit breaker and lamp are good.
If the lamp does not illuminate, further testing is required. I like to use a 12 volt test light similar to this one:
http://www.autozone.com/autozone/accessories/Innova-Transparent-handle-test-light-circuit-tester/_/N-2714?itemIdentifier=186543_0_0_
Connect the test light clamp to ground and test the output of the circuit breaker with the test light probe. Of course the master switch needs to be on for this test. If there is voltage at the circuit breaker, then probe the lamp. If the lamp is getting power but does not illuminate, the bulb or socket could be bad. Do not replace the circuit breaker unless testing proves that it is bad.
Joe Gores
 
SD-20 Light testing

Hi Joe

I did that yesterday and the light does come on if I press on it and I also tested both Circuit Breaker ( The one for the light ( 2 Amps ) and also the one for the field ( 5 Amps ) and both are working as they should...

I tested the alternator today in flight by pulling the breaker of the main alternator field so I could get the stand by to pick up the load and it did ( looking at the load on the amp meter ) but the light still did not come on to say the stand by was working .

Something I noticed today though was the voltage supplied by the SD-20 at 2400 engine RPM. The voltage was only 12.5, 12.6 volts and as far as I know the SD-20 should be providing something like 13.7 when used as a back up alternator.

Maybe the voltage regulator is set too low.. and the light is supposed to come on as 13 volts is I remember properly..

What do you guys think, anyone installed one and could confirm this.

If this doesn't work then I don't know what to think to be honest.I guess a call to B&C will be in order at that point.

Thank you for your feedbacks, greatly appreciated

Bruno
 
I did that yesterday and the light does come on if I press on it and I also tested both Circuit Breaker
Click to expand...
I do not understand. What did you do yesterday? Did you disconnect the wire from regulator terminal 5 and ground the wire? If so, did the light come on then? If so, then the problem is within the voltage regulator.
Where is the current sensor located? Depending on its location, it could be sensing battery discharge current and not alternator output current. Unless there is a very heavy load, a voltage of 12.5 indicates that neither alternator is supplying current. B&C can give helpful advice for checking out their products.
Joe Gores
 
SD-20 TROUBLE SHOOTING

Hi Guys

Alton: I have the SB1B-14 regulator installed with the Hall effect current sensor installed as per B&C instructions.

I think I may have to adjust mine like you did with yours.

I will give B&C a call to confirm the wiring and the way it operates right now before doing anything..
------------
JOE
The current sensor is the one supplied by B&C and is fully assembled when you get it.
It is connect as per their instructions ( verified twice )so it shouldn't be the problem.
I will verified the wire from Pin 5 again when I go back to the hangar sometimes this week just to make sure.

I'll keep you updated.

Thanks

Bruno
 
You must log in or register to reply here.
Back
Top