Over voltage required for EarthX battery

[jaredyates]

Kalibr, I wasn't meaning to implicate your responses there... I'm continuing the discussion via PM with the member I was thinking of.

[Blain]

Maybe some clarification for a EarthX user.

Using a Denso alternator. Concerned about runaway voltage lighting off the LiPo bomb (kidding). On firewall so a bit safer then the aircraft that started this thread.

Also have a AFS 4500 so I assume it will yell at me if voltage exceeds XX? I'll check settings when I get to hangar.

Now if I understand what I've read so far, the field wire that I have after a breaker and toggle switch is only a signal? That the field actual draws necessary current from the B lead? So disconnection of the field wire will not stop a runaway alternator? Again, in this case, a Denso, same as Vans.

Enlighten me, please.

[Chkaharyer99]

Originally Posted by Blain

Also have a AFS 4500 so I assume it will yell at me if voltage exceeds XX?

I have an AFS 4500 and it has an alarm/alert for low voltage. It worked on one occasion when I left my Alt field switch off and flew for about 15 mins in that condition.

It also has a high voltage alarm but I've never heard it alert.

[jliltd]

We bought an Earth-X battery frok Wicks at Oshkosh 2017. Ended up triggering a BMS Earth-X warning on the G3X GEA 28 interface LRU. Called Kathy af Earth-X and couldn't be more impressed. First off a real human in charge answered the phone and determined that based on our serial number the battery we bought was very old without the latest battery monitoring software with the sensitivities updated for G3X compatibility. So Kathy took the time to make the problem her own (as is appropriate) and didn't hesitate to send out a brand new unit at no cost for exchange. She was super cool and totally involved. A very human experience. A breath of fresh air that harkens back to a time when a manufacturers stood behind their products and focused on customers. Not even a whiff of back room bean counters screwing the whole thing up. You are talking to a person where the buck stops. No blow offs. No excuses. Just factual interaction with a new friend. This is almost too good to be true. I dearly hope that Earth-X can expand upon the volume of happy customers without becoming just another modern company.

Meanwhile the new replacement was exactly as promised. Works great without B. Betty complaining about it.

Jim

[DanH]

Originally Posted by Blain

Now if I understand what I've read so far, the field wire that I have after a breaker and toggle switch is only a signal? That the field actual draws necessary current from the B lead? So disconnection of the field wire will not stop a runaway alternator? Again, in this case, a Denso, same as Vans. Enlighten me, please.

The field wire is a power supply. The issue is how the internal voltage regulator is designed.

Traditional auto alternators of this type draw power via the field wire for initial excitement during startup, then switch to self-excitement at operating RPM. That's not exactly the same thing as "draws from the B-lead", but conceptually close enough...after start, the field gets its power internally, via the regulator.

The preferred alternator for our application always draws all its field power via the field wire/switch/breaker. An overvoltage device installed in that field line will sense voltage rising above the desired level, and disconnect the field power almost instantly by shorting the field line to ground and popping the breaker.

A Plane Power has the OV device built into the internal regulator, same function.

Assuming you do not have a Plane Power, here is the easy test to determine what you do have. Turn on the master. Note buss voltage, which is battery voltage alone. Now fire up the engine. With the alternator switch and breaker closed, buss voltage will rise to some higher figure, typically 13.8 to 14.5V. Now, with the engine running, open the field switch or pull the breaker. If buss voltage does not drop back to battery voltage, you must wire a disconnect contactor in the B-lead. If buss voltage does drop back to battery voltage, wire an OV device into the field lead.

[Blain]

Originally Posted by DanH

The field wire is a power supply. The issue is how the internal voltage regulator is designed.

Traditional auto alternators of this type draw power via the field wire for initial excitement during startup, then switch to self-excitement at operating RPM. That's not exactly the same thing as "draws from the B-lead", but conceptually close enough...after start, the field gets its power internally, via the regulator.

The preferred alternator for our application always draws all its field power via the field wire/switch/breaker. An overvoltage device installed in that field line will sense voltage rising above the desired level, and disconnect the field power almost instantly by shorting the field line to ground and popping the breaker.

A Plane Power has the OV device built into the internal regulator, same function.

Assuming you do not have a Plane Power, here is the easy test to determine what you do have. Turn on the master. Note buss voltage, which is battery voltage alone. Now fire up the engine. With the alternator switch and breaker closed, buss voltage will rise to some higher figure, typically 13.8 to 14.5V. Now, with the engine running, open the field switch or pull the breaker. If buss voltage does not drop back to battery voltage, you must wire a disconnect contactor in the B-lead. If buss voltage does drop back to battery voltage, wire an OV device into the field lead.

Thank you, Dan. Now I get it.
Do you suppose with the EFIS screaming "Check voltage" the meat servo could react fast enough to keep from frying the EarthX?

[Bill Boyd]

Originally Posted by DanH

The field wire is a power supply. The issue is how the internal voltage regulator is designed.

Traditional auto alternators of this type draw power via the field wire for initial excitement during startup, then switch to self-excitement at operating RPM. That's not exactly the same thing as "draws from the B-lead", but conceptually close enough...after start, the field gets its power internally, via the regulator.

The preferred alternator for our application always draws all its field power via the field wire/switch/breaker. An overvoltage device installed in that field line will sense voltage rising above the desired level, and disconnect the field power almost instantly by shorting the field line to ground and popping the breaker.

A Plane Power has the OV device built into the internal regulator, same function.

Assuming you do not have a Plane Power, here is the easy test to determine what you do have. Turn on the master. Note buss voltage, which is battery voltage alone. Now fire up the engine. With the alternator switch and breaker closed, buss voltage will rise to some higher figure, typically 13.8 to 14.5V. Now, with the engine running, open the field switch or pull the breaker. If buss voltage does not drop back to battery voltage, you must wire a disconnect contactor in the B-lead. If buss voltage does drop back to battery voltage, wire an OV device into the field lead.

Keep in mind there's been some speculation that a regulator _could_ fail in some way that changes this behavior - a unit that formerly powered down with removal of external field current when tested _might_ become non-controllable in the event something fries internally. (Can't prove a negative and there's no way to know for sure.) For this reason, even though my IR Denso alternator does power down when I open the field switch, my crowbar circuit from now on both trips the field breaker and opens a B-lead contactor. Belt and suspenders.

[bobnoffs]

blain,
i am counting on a pilot's reaction to be ample to disconnect the charging source from a battery before the battery goes over the edge.my system is designed for 2 earth x batteries.i think i have plenty of time after a flashing light to turn off the field and pull [push pull type] the breaker that disconnects the alternator's charge from the battery.the instant response used to be required [so the old beliefs go] that the avionics would/could be fried by anything slower than a crowbar device.

[DanH]

Originally Posted by Blain

Thank you, Dan. Now I get it.
Do you suppose with the EFIS screaming "Check voltage" the meat servo could react fast enough to keep from frying the EarthX?

Can't speak for the EarthX, but you might fry some avionics.

Given the low cost and simplicity of OV devices, going without is like trusting a fart.

[rv7charlie]

Originally Posted by Bill Boyd

Keep in mind there's been some speculation that a regulator _could_ fail in some way that changes this behavior - a unit that formerly powered down with removal of external field current when tested _might_ become non-controllable in the event something fries internally. (Can't prove a negative and there's no way to know for sure.) For this reason, even though my IR Denso alternator does power down when I open the field switch, my crowbar circuit from now on both trips the field breaker and opens a B-lead contactor. Belt and suspenders.

Hi Bill; hope you don't mind me quoting you to expand on that.

I hope this pic link works; I tried to copy it from a post by Ross F in another thread.
http://www.vansairforce.com/communit...6&postcount=55

The line labeled 'S' is the control line to the regulator (what almost everyone here is calling the 'field terminal').

Look down & right, at the coil symbol at the bottom of the image (below the star-shaped 3-coil system). This is the field winding in the alternator. Note that the wire from the left end of the coil is tied directly to 3 diodes, fed by that 3-coil network. This is DC going to the B-lead (output) of the alternator. Note also that this B-lead voltage is fed directly into the 'IC regulator'.

Now follow the wire from the other end of the coil, into the blank box labeled 'IC regulator'. In order for the field winding to generate a magnetic field (which, along with rotation, is what makes the alternator make power), that DC path must be completed to ground. It's not shown in the drawing, but inside that blank box there's a transistor that is a 'gate keeper', and controls the current flowing through the field winding and out of the blank box, on the wire just below the coil, to the ground symbol in the drawing.

Here's the point of all this:

If that (undrawn) 'gate keeper' transistor shorts out, ask yourself what happens to the field current. Then ask yourself how you shut down the alternator, with that transistor shorted.

Now, there may be some internally regulated alternators on the market that aren't wired this way. But I hope it's obvious that with this particular design, if the regulator fails, there is no certainty that it can be shut down by removing power from the 'field' terminal. It should also be obvious that being able to shut it down using the 'field' terminal *while it's working properly* is no guarantee that you'll be able to do it after a regulator failure (which is what causes an overvoltage event).