B&C SD8 alternator will quit if battery is disconnected?

A while ago I posted a question about the SD8 Stand-by alternator. To allow the alternator failure-light to also show when the alternator is not putting out power, I want to put a diode between the alternator and the battery. See my post: http://www.vansairforce.com/community/showthread.php?t=30442
I did not get a satisfactory answer.

Now I have just received all the goodies from B&C, but I am very surprised to read the following in the trouble shooting hints of the SD8 manual:

In case of no operation: "The battery may be disconnected from the PMR1 (regulator), thereby disabling the regulator circuitry".

Does this mean, if the battery is disconnected, switched off, or "dead" the SD8 will not put out power to the equipment that is connected to it? (would this not mean that the SD8 can not recharge a flat battery?)
Hey, the idea was that if anything happens (a dead battery?) the SD8 is always there as a back-up.
Anyway, if that is indeed the case, my diode may disable the SD8, because it will restrict power from the battery, back to the regulator.

At the time, I did call B&C, but did not get an answer from them regarding the diode in my diagram, either, because they just did not know how it works! Apparently the only guy who could knows this, has left the company!?.

Any clever people out there who can tell me more about how the SD8 alternator/regulator works?

Regards, Tonny

Its a Bootstrap Thing

The PMR1 regulator needs some initial power to start doing it's thing. Once it is working and the SD8 is on line, it no longer needs the battery. There is quite a bit of discussion about the SD8 on the aeroelectric connection mailing list and there is a diagram (Z-25) showing a configuration of the SD8 where it will "self excite" without a battery.

As I recall, the SD 8 is a perm magnet dynamo. It will have an output (a/c) anytime it is turning. It is a really simple device.

Now, as to what I suspect your question is really asking, will the system, (SD 8 plus regulator/controller) work without the battery.

Yes, if you wire it up to do so. And no, if you wire it not to.

Lotta help, I know.

The key to the question is that the relay used for control is needed to let the "crowbar" circuitry disconnect things. In a normal alternator, the field is excited by a switched current through the "field" breaker and switch.

The SD 8 doesnt have a field, so they have to switch the regulated/rectified output, and not the field input, to turn the system on or off.

Hope this helps.

No it will not! I tested it!

Yesterday I tested the SD8 to make sure I understand how it worksand get the answers I could not get anywhere else.

I put it in the vice of my drill press and connected it to the drill chuck with a plastic hose as a flexible coupling and wired everything up according the Aero Electric diagram. I used the Dynon EMS to display the Amps from the shunt.



I also tested the diagram, with a diode, that I thought would allow the relay to switch the light on when the alternator is not putting out any power. Here is what I learned:

• The 4Ah SLA battery works fine with the SD8, it did not overheat, even after allowing the battery to drain for an hour or so, back to 10,5 V (using a 12 V-50W bulb, which you can see in the picture is beeing held by a "third hand"). The SD8 will initially put out approx. 8 Amp. and go back down to a couple of amps when the voltage rises.
• The SD8 will put out power immediately if the battery is connected. However, if the battery is, initionally, not connected, the regulator will not start!
• The SD8, connected to my diagram, with a diode between it and the battery, will not start on its own. Just a 'flick" with a wire from the battery to the + of the regulator and it comes alive. Ones it is running you can remove the battery and it will keep putting out power. The voltage is less steady than with the battery connected and wanders between 14,5 and 15,5 V. But it's good to know that if, for some reason, the battery is disconnected or "kaput" the alternator will keep feeding the Electronic ignition. One more reason not to connect the EI to the battery, but to the bus.
• There was a 0,8 V drop across the diode that I was using (15 A, 200 V), causing the charging current to be much less than without the diode, thus charging the battery a lot slower. This could be rectified by adjusting the regulator, but I choose not to do that.

I know there is a "self agitating" circuit on the Aero Connection webiste, but it's more complicated. So I decided not to use the diode, but go for the standard circuit. I can monitor the Voltage on the EFIS (back-up power) and use a switch to monitor the current on the EMS (switch between Main and Aux), if necessary.

I hope others can learn form this to, but use the information at your own risk!

Regards, Tonny

Yes I have read

a lot about this..after I installed the SD8 the standard (non-self exciting) way.

But then I had to think why would I need it to be self exciting?..I mean I have an audible alarm on the Dynon EMS that tells me the battery volts has dropped to 12V, which it will do pretty quickly.

So there should be plenty of oomph in the battery to excite the SD8.

I run a plane power primary and the SD8 as the backup and run electric fuel pumps only..No mechanical pump.

Oh an I fly IFR..I have proven the SD8 will run the GNs 430, transponder, single fuel pump and the Dynon EMS (the D100 is battery backup up) and holds 12 Volts at 2600RPM.

If you add this lot up it comes to about 12Amps..Not a bad little unit..

Frank

I left the master on and needed a jump to start my RV6 one dark night away from home. The engine started and I used minimal intstruments to help recharge the battery as I taxied out and launched with only position lights (no taxi or landing light).
Every thing seemed just fine until I turned on my landing light in the pattern at my home airport. Everything went black. The landing went fine as per training, I had to use a flashlight to taxi.

What happened was that we jumped the engine at the solenoid on the engine/instrument terminal side, no juice ever reached the battery. The battery had no power to hold the solenoid closed to recharge the battery. The isolated alternator and instruments were just fine until I overloaded the alternator breaker by switching on the landing light.

Question?

I have just completed the first run up with my Plane Power-IO-360 RV-7, I show a 4-5amp draw from the alternator when powering up before start. Is this normal?? Do you leave the Alt. Field breaker pulled until start??

I have gone over the wiring, it all done per drawings, everything else works well.

Thanks for your time.

Steve