Calling all electrical "experts" please.

I have a semi-unique situation/question. I'd appreciate any input (especially from Dan (Horton) that all know about as I have done so many of his recommendations). I designed my electrical system about 15yrs ago using Bob's Z-13 wiring diagram (with some changes) for my 8. Please see attachment. Was basically running a 680 battery, SD-8 backup and dual Plasma I (like Plasma III) electronic ignitions. One of the major changes I did was connected the ignition wires directly to/from the battery (with fuselink to the breakers) without going through any buses as I wanted the most direct simple path for the ignition in the event of any electrical problems.

Fast forward to about five years ago when I replaced the 680 with a lithium battery from Aerovoltz (love their batteries). I used that battery for 4 1/2 years with no problems; but that was when they first came out and didn't have all of the internal protections that they have now. About 7 months ago I switched to their updated/upgraded battery (AVAI-480), which has all the bells and whistles as far as protection goes. I thought that would be better than having no protection and thought, though nothing wrong with the old battery, probably time for a change.

Getting ready to do my annual and there are couple things I have thought about, but haven't "fixed" yet to have a good reliable backup in case something happens to the battery. Since doing the annual, now is the time to get er done, and should have done it when installed the nice high feature battery!

Several of my concerns are if I get a low voltage warning from my voltage regulator from B&C, it is set to 12.7 volts. That's ok for a lead acid battery, but very bad for a lithium battery as there will be very little stored power at 12.7V (something different between the two batteries). B&C has said no problem for them to adjust that higher on the VR. Maybe 13.2 or 13.3V -- whatever I want. Not sure what I want? I do know that sometimes when I land and pull the power back to idle, I will get the low voltage warning. I just turn off the fuel pump and wig wags and it goes away. Don't really want to have that warning come on on short final because the warning has been changed/bumped higher. Normally not at idle on final, but think you get what I mean.

A bigger concern is if the battery has an auto shutdown for some reason, I wouldn't be able to excite the SD-8 (switch must be turned on) because once that battery turns off, it won't accept power (from the SD-8) or deliver power (to the ignitions since connected directly to the battery) -- not good! It depends on which gate it gets turned off for as to whether it will turn back on once the condition goes away. Low voltage it won't get turned back on until it's reset on ground (or I can make a pushbutton reset for in air, but not imperative if I have a good backup).

Have read a lot of info on the forums. The TCW seems like a good option, but I also like Dan's thought of almost a regular sized battery (though space is very limited in the 8 as he and we all know). Doesn't matter how it's mounted and very, very light in weight, so I would be able to make that happen.

Just trying to figure out the easiest and most reliable way of doing this given the SD-8, dual EI and ignition wires connected directly to the battery. Was very comfortable with this set-up with a lead acid battery, but am very uncomfortable now with the newer lithium batteries and their auto shutdown features. I believe the EarthX batteries are the same?

I wonder if maybe the easiest thing to do is add a same size battery with a battery switch or some kind of rigged up automatic switch over feature so no interruption (if that's even possible)? Have to probably do something with those directly connected ignition wires to the main battery also.

Thoughts? Thanks guys (and Dan I hope)

Attachment size

Looks like the attachment might be a little hard to see? Not sure what to do about that? If anybody wants to see it in detail, feel free to email me at [email protected] Might not even be important to see it given the explanation? Thank you.

Dave,

You have identified the Achilles Heel of a ship power dependent engine and single battery install. As you rolled the dice on this setup for several years, consider yourself lucky and go by a lottery ticket.

As you point out, the proper approach is to have one ignition wired directly to two identical batteries (I use PC-625s in my projects). The two ship battery step provides for direct power for your ignitions, greatly simplifies maintenance and offers options for providing redundant power delivery to your panel (well suited for IFR work).

On my RV-8 I have one PC-625 mounted in the forward baggage compartment well, and one in the normal aft location. For my IO-360-M1B, Hartzell BS prop and Grove Gear, the W&B worked out very well. For normal operations both batteries are run in parallel with the alternator. The panel gets power from each battery on the battery side of the master solenoid, each half the panel on one battery (the battery is selectable). On any electrical fault POH immediate action is to open both master solenoids. This isolates each battery establishing the mosl reliable configuration. Battery capacity is adequate for 2-3 hour of continued IFR flight. On this RV-8 I do have the nice MonkWorx generator on the vacuum pad as the standby alternator.

I share your concern about ship power dependent engines and any of the lithium options. A BMS that shuts down the battery as self protection, resulting in the fan stopping, is not an attractive system design feature.

I replace one PC-625 every three years - so that neither battery exceeds six years of service. This is the best way to have confidence in battery reserve capacity. The pulled batteries go on to a second life in one of the neighbor’s John Deer.

Carl

...and

"...I share your concern about ship power dependent engines and any of the lithium options. A BMS that shuts down the battery as self protection, resulting in the fan stopping, is not an attractive system design feature..."

...and a lithium fire from a battery that doesn't protect itself is worse.

Unless there is a manufacturing fault in the BMS, there are not many ways that this can happen. One example is:

The BMS is set to disconnect at 16.0 volts for 2 seconds. The OV protection in the voltage regulator is set to 16 +/-0.25 volts, and should trip in around 40 milliseconds. IF the regulator senses 16.1 volts and it is on the high side of the set point range, the OV protection in the regulator doesn't trip the alternator field. This allows the battery BMS to see a voltage greater than the 16.0 v trip point, and will likely see it for the requisite 2 seconds. The BMS then takes the battery offline. In a normal situation, the OV protection in the regulator would trip the alternator field long before the 2 second delay required for the BMS to take the battery offline.

It would seem that an obvious solution would be to reduce the OV set point voltage in the regulator, thereby ensuring an OV trip before the BMS could disconnect the battery. An OV set point of 15.8 +/-.25v would probably work just fine and eliminate the possibility described above, while maintaining a high enough threshold to prevent nuisance trips.

Again, it comes down to risk mitigation. There is no possible way to design or build a perfect system; if you drill down deep enough, there will ALWAYS be a potential unacceptable failure mode.

I'm surprised the previous guys didn't mention replacing the SD-8 with a Monkworkz; PM generator that doesn't require excitation.

Was looking to install a Thielert engine (which gives you an idea about how long ago) and had to look at the scenario of a single battery having the battery become disconnected. At the time they were lead acid, but the concern was that the battery cable had become a single point of failure which is pretty much what happens when the LIPO goes into protection mode.

While I'm with Carl in that I'd really prefer a dual bus, or at least two batteries, the solution at that time was to add a small sealed lead acid battery isolated with a diode ( 1 or 2 aH) to the system who's only job was to excite the alternator, that way if you lost the main battery you would have a way to get the system back up, and keep the watts flowing indefinitely. It can be quite small since as soon as the alternator starts working again, it starts getting charged from the bus through the isolating diode.

Its probably the smallest change to your existing system that gets you back to the original design.

Edit: or this

Freemasm said:

I'm surprised the previous guys didn't mention replacing the SD-8 with a Monkworkz; PM generator that doesn't require excitation.

Click to expand...

Wow. Great responses guys. Thank you.

Yes Carl (and Bob and Derek). I was on borrowed time but felt comfortable given the SD-8 and lead acid battery. My thought was I'd get the low voltage warning and simply (never simple, right) flip the switch to excite and go to essential power (very reduced minimal loading), and I could land ASAP. Lead acid batteries generally don't just go dead and turn off like lithium. As mentioned, it's all a risk mitigation thing. Gonna continue to watch this post and come up with a solution.

There is a work around I believe to get the SD-8 excited (through Z-25 diagram) automatically (spoke with TJ at B&C) that some of Bob Nuckoll's followers came up with (rather clever according to TJ).

I'm not the sharpest electrical guy, but I can follow a wiring diagram to make it all work once something is figured out Thx.

Hi Dave. Good to hear from you.

Have a thread going right now with a system design partially driven by the switch to EarthX or similar with an internal BMS. Like you, I was concerned with the possibility of the batteries going off line. You'll find a Monkworkz MZ-30L set up with a DPST switch and a relay or contactor, which allows it to reside on the hot side of the contactor without draining the battery when parked (regulator has a parasitic draw).

When enabled (switch contacts closed), it wakes itself when the battery side voltage drops below its set point. Battery voltage can be low (main alternator off line) or zero (main off line and a BMS disconnect). Either way it should pick up the ignition load attached to that battery. Self starting, and current limited at 30 amps.

I do recall someone cooking a way to make an SD-8 do the same, but I've not explored the option.

rocketman1988 said:

"SNIP….In a normal situation, the OV protection in the regulator would trip the alternator field long before the 2 second delay required for the BMS to take the battery offline.

Again, it comes down to risk mitigation. There is no possible way to design or build a perfect system; if you drill down deep enough, there will ALWAYS be a potential unacceptable failure mode.

Click to expand...

Assuming the OV protection works. In the one and only alternator over voltage incident I had the OV protection did not work. My Odyssey batteries sat there and absorbed the over voltage condition long enough for me to figure out what was going on so I could trip the alternator. This took a lot longer than a few seconds as I suspect it would for anyone. Buss voltage was well north of 17vdc.

Careful design will mitigate probable failure risks.

Carl

Carl Froehlich said:

Assuming the OV protection works. In the one and only alternator over voltage incident I had the OV protection did not work.

Click to expand...

Perhaps a useful data point. What sort of OV protection was it?

DanH said:

Perhaps a useful data point. What sort of OV protection was it?

Click to expand...

Alternator output routed to and firewall mounted solenoid. The solenoid powered via a 5amp pull breaker - that had a crowbar circuit to trip the breaker on over voltage to open the output solenoid (right out of Nuckoll’s book at the time).

Carl

I would use two batteries, each with its own contactor and switch, to feed a main bus and power electronic ignition from the main bus. Battery and contactor/switch redundancy essentially eliminates the risk of losing battery power and the ability to isolate a faulted battery from the bus eliminates the problem with direct battery-to-ignition setup.

So...

Carl Froehlich said:

Alternator output routed to and firewall mounted solenoid. The solenoid powered via a 5amp pull breaker - that had a crowbar circuit to trip the breaker on over voltage to open the output solenoid (right out of Nuckoll’s book at the time).

Carl

Click to expand...

So now we can't rely on OV protection, either?

Getting kind of ridiculous...

Freemasm said:

I'm surprised the previous guys didn't mention replacing the SD-8 with a Monkworkz; PM generator that doesn't require excitation.

Click to expand...

SD-8 can be wired to not require external excitation. Knuckles has a drawing with parts to do this. Think it required a rectifier bridge, as the SD-8 output is AC and the VR does the conversion to DC, unlike a typical alternator that has the bridge /conversion built in.

Possibly partial good news

All good points and appreciate you jumping in too Dan.

Was chatting with a buddy today and he brought up a very good point. It might be a moot point about the battery dropping off and then the SD-8 being of no use.

If you look at the wiring diagram (as you can see from the first thread post), the SD-8 power (when energized) goes to the left side of the battery contactor directly to the battery. Since the leads for the electronic ignition are attached to the same post as the wire from the battery contactor post (and then to the SD-8), through physical contact, it shouldn't matter what happens to the battery theoretically because the juice will just continue past the battery?

Next time I am at the hangar, I plan on testing this on the ground, which should be very easy to do. Will start the engine with battery master, then excite the SD-8, and then turn off the battery and see what happens. I know the more RPMs there are on the engine, the more amps the SD-8 will produce. We'll see what happens. Thx. It's better news if it does work (like it use to), but still am going to figure out a new/better way.

db8 said:

All good points and appreciate you jumping in too Dan.

Was chatting with a buddy today and he brought up a very good point. It might be a moot point about the battery dropping off and then the SD-8 being of no use.

If you look at the wiring diagram (as you can see from the first thread post), the SD-8 power (when energized) goes to the left side of the battery contactor directly to the battery. Since the leads for the electronic ignition are attached to the same post as the wire from the battery contactor post (and then to the SD-8), through physical contact, it shouldn't matter what happens to the battery theoretically because the juice will just continue past the battery?

Next time I am at the hangar, I plan on testing this on the ground, which should be very easy to do. Will start the engine with battery master, then excite the SD-8, and then turn off the battery and see what happens. I know the more RPMs there are on the engine, the more amps the SD-8 will produce. We'll see what happens. Thx. It's better news if it does work (like it use to), but still am going to figure out a new/better way.

Click to expand...

So run the system with no battery?
A good chance of the system going overvoltage is my prediction.

No battery on line!

What happens when you disconnect the battery from the power bus with the
alternator connected.
The voltage regulator will then have a difficult situation to maintain the voltage set point 14 V.
You can compare it with the water tower in your city.
The water comes from a lake and is supplied to the water tower (reservoir) by pumps. Your kitchen tap is connected to the water tower.
Removing the water tower from the line, will cause large pressure variations
on the tap in your kitchen. This is because the user side flow is changing.
Any change in the demand of water/ amps from the user side will cause
lower or higher pressure/ voltage.
Modern avionics have built in over voltage protection BUT there is a limit
where the protection just can´t stand it. 30 V to a 14 V fuel pump ?

Modern aircraft with electronic ignition, fuel injection and EFIS only
demands a stronger electric system than the old C172.
This would probably require dual everything, batteries, alternators and power buses. It depends on what level of safety you require.

Good luck




Good luck

Agree with Freemasm

The more specific performance range of the Lithium battery is telling you the SD8 is not providing power at or around idle (by design). Its a good backup Alt but not designed for what you are using it for. Too many slices of cheese lined up before you take off. Twin Batteries or Twin Alternators go well with Electronic Ignition

lr172 said:

SD-8 can be wired to not require external excitation. Knuckles has a drawing with parts to do this. Think it required a rectifier bridge, as the SD-8 output is AC and the VR does the conversion to DC, unlike a typical alternator that has the bridge /conversion built in.

Click to expand...

@ Larry, I respect your knowledgeable opinion as always. While I can't prove this statement, I do not believe the SD-8 was ever intended to keep an electrically dependent aircraft airborne. More likely, it was probably intended to keep some critical avionics lit.

A little drift but I expect the Monkworkz product to kill most everything in the related market. Over 3X the output from essentially a self contained unit at only a marginal cost delta and slightly less weight. We'll see what the competition does to try and keep up.

I love market disruptors. Besides the tech gains, they help keep their related market honest.

Come on weekend.

Blaplante, wouldn't obviously want to do that in my situation and that might have been said tongue & cheek.

Freeman, I know when I was doing the research on the SD-8 many years ago, I believe Bob (from B&C) said it was originally designed for the cub or some small plane without a battery to run a radio or small electrical item (whenever engine running). That might be good and true for that situation, but it's turned into a good choice as a backup in our homebuilt application (I believe).

Avanza, nice analogy. Like it when it is put in simple terms like that. Don't think I can have the alt field on AND the battery off with the setup I have through manipulating any switches.

VNS - thinking an extra battery thing might be best. Very unlikely but if the main battery failed (lithium), the engine quit (say with duel EI) and wasn't windmilling, how would you get the power to energize the ignition for a restart, even with a SD-8 or Monkworkz because they are tied into an operating engine (not sure if they would produce enough power with a windmilling prop)? You couldn't, could you?

I did install the voltage regulator for the SD-8 and the capacitor. I'm just looking for something that can keep the engine/backup attitude indicator (the other thing I have connected to the battery directly through a fuseling and switch breaker) till I land.

Freemasm said:

@ Larry, I respect your knowledgeable opinion as always. While I can't prove this statement, I do not believe the SD-8 was ever intended to keep an electrically dependent aircraft airborne. More likely, it was probably intended to keep some critical avionics lit.

A little drift but I expect the Monkworkz product to kill most everything in the related market. Over 3X the output from essentially a self contained unit at only a marginal cost delta and slightly less weight. We'll see what the competition does to try and keep up.

I love market disruptors. Besides the tech gains, they help keep their related market honest.

Come on weekend.

Click to expand...

The intentions of it's design is really not relevant. The SD-8 has pros and cons and the DESIGNER needs to determine how it will fit into a design and the unique goals of that design. I have one (a homemade version almost identical) and 8 amps is enough in my design to support flight in my elec dependent plane in a worse case scenario.

I was not suggesting that this be used for anyone's redundancy plan, only disputing an incorrect claim that this unit required an external power source to get it to work

db8 said:

All good points and appreciate you jumping in too
If you look at the wiring diagram (as you can see from the first thread post), the SD-8 power (when energized) goes to the left side of the battery contactor directly to the battery. Since the leads for the electronic ignition are attached to the same post as the wire from the battery contactor post (and then to the SD-8), through physical contact, it shouldn't matter what happens to the battery theoretically because the juice will just continue past the battery?

Click to expand...

Hi Dave,


A little more from my story for you. Since changing the electrical system required updating a whole bunch of documents, the first thought we had exactly yours. Since we were in a program, we did of course have to test the theory. The test matrix was planned for a few days, and the the first few tests went well, but we eventually fell down even without introducing a second failure (which was out of scope). Different airplane, different equipment so you may get different results.

I won't tell you that you need a full deal dual system, indeed there are electrically dependent certified airplanes that don't, but I wouldn't be comfortable flying after just a single test on an alternator without a battery, in an airplane that is electrically dependent.

Consider in your case, which is a bit worse than a simple disconnect of the battery if the BMS kicks off, since odds are pretty good the either something bad has happened to the battery or the electrical system immediately prior, so you many not be starting from a stable system.

Try also to consider the worst practical cases and consider testing those.

For example, you are at low RPM on approach (the most exciting time for a further failure), and then hit any and all high load items. Don't assume the pilot won't brain fog and be smart enough while heavily saturated to not do that. At a minimum you will know which switches to be scared of in that mode.

I don't know, and I've never read any analysis what the transient voltages are going to look like but its a fair assumption that there will be a lot more noise in the system with the battery disconnected. Flipping big loads around, may or may not create voltages that could break things - in an emergency we live with it, during testing we like to keep costs down. Consider turning the expensive stuff off and using more tolerant loads like landings lights, pitot, motors as a proxy for things like com transmit and other loads, at least for the 1st tests.

Let us know how it goes.

Derek

Love this forum!

Ir172. Not sure if when you say "this unit" if you are referencing the SD-8 or Monkworkz. All I do know for a fact is the SD-8 must be excited to work. There is a work around where that can happen (I believe automatically). I'm just repeating what TJ said a couple of days ago from B&C when I first started looking into this (and before the post).

Derek, all great, realistic points that need to be taken into consideration. Completely agree there will be more "noise" in the system with the battery gone (TJ even mentioned that). Am going out to crank her up today and I like your thinking. One of the tests (second one) I was going to try was see if the essential bus would pick up the load with the throttle pushed up (SD-8 excited, battery off and switch position in "essential power"). Can look in notes but think the load was maybe 4 amps without the EI. Am not going to do that test now because of your good points on possibly harming some components (if I took that correctly). And, that doesn't really matter because I am going to add something more substantial (like an extra battery) to pick up that essential power load in a true deteriorating situation. I did do all this within first 10 or so hours and it worked fine 12 years ago, but that was momentary and haven't messed with it since. I will, however, see if it will pick up the electronic ignition and stby attitude indicator (not continuing the switch forward to the "essential bus" position). Don't think it will harm them and will do it only momentarily. Then will test it in the air at altitude once I get the other backup in place (again thinking second battery - considering size now).

Thanks gents. A bit of a slippery slope as lots of different good suggestions here, and when I do go with what I go with, so people are going to question it. All good though because that's what home building is all about! Do the research, listen to those smarter than you, and go with which one you like!!

Started up the plane, excited the SD-8, turned off the battery (which also had the alternator off line) and the SD-8 had no problem at any RPM keeping the engine running - both EI's and stby att had no glitches or hiccups. I should really check this at least once a year at annual (or maybe more often -- don't think each flight or anything).

Given this result (like when I first checked it in 2011), I am looking at adding a smaller battery as a second backup (or should I really say 1st backup for it and second backup for the SD-8). The TCW 6ah battery looks pretty good, but will have to do some research. Will have to try to figure out where/what configuration the electronic ignition, stby attitude indicator and the SD-8 wires need to be placed or changed to optimize the new system. As mentioned earlier, not an electrical expert but can certainly follow a wiring diagram when building a harness/electrical system.

Thanks in advance for any thoughts and discussions.

Exciting the SD-8

I found this drawing from many years ago that solved the problem of exciting the SD-8 independently from the main battery. I used a small .8 ah battery that is about the size of a deck of cards and an oil pressure switch to prevent it from discharging between flights. I tried the self exciting circuit that Bob Nuchols suggested, but the voltage was very unstable.

View attachment Standby Alternator System.pdf

Good to know Ken. Thanks for posting that.

Trying to think about keeping the "update/upgrade" as least intrusive to the existing wiring as possible. I'm ok with self exciting the SD-8 with a switch, especially knowing I'm adding an extra battery, along with the use of the current battery and voltage warning before the main battery drops off. I just need to look at my essential bus (how many amps), and use the added battery to run it and the SD-8 backup for the electronic ignitions and STBY att.

Hi Dave,

I like the TCW kit, and have one in my Glasair. If you just want a reliable battery setup you can put it between the ESS and one ECU and the ATT and it will give you a simple reliable last chance backup until the battery runs out.

You can ask TCW but I suspect they will advise against have the the SD-8 on the "backup" side of their box, since the charging is meant to come in through pin 5.

If you want to energize the SD-8, Ken's approach is likely the cleanest with the fewest changes. You could also just use a "SD8 energize" switch to replace the oil switch. The main reason its on the oil switch I suspect is to make sure its charged when you need it. A good checklist could be a alternate for that.

All depends on what you want to do and feel comfortable with.

Derek

Silly me

As per my post on 2/24 (test run), I could have turned off the SD-8 and the engine would have still been running. Know why?

Just because I turned off the ALT field and battery master switch (and had the SD-8 excited), that didn't mean the three things (L & R ignitions wires and Stby Att wire) connected directly to the battery positive post were running on the SD-8 only. They WERE running on battery power because they were directly connected to an operational battery! So, the test was basically worthless.

There is no way (that I can think of) to truly test the SD-8 in my configuration (two EIs and Stby att connected directly to battery) unless the BMS turns it off? Anybody disagree with that statement? I'm not saying it's absolutely correct, but that's my best guess.

I have decided to keep this "fix" simple.

1) I have sent the B&C regulator to them to increase the low voltage warning light to come on from 12.7V (lead acid battery) to 13.4V (Lithium battery). I could pick any number but TJ and I came up with the 13.4) since the regulator should keep the charge at 14.4V.

2) Looking at changing voltage warning in EIS and EFIS also.

3) Get the TCW Technologies 6ah backup battery to run one of the EIs, while leaving the other EI and Stby Att like it is.

Will leave the SD-8 just like it is also. If/when I get the low voltage warning (13.4V), I'll excite the SD-8 and start troubleshoot the problem. Depending if in VMC or IMC or how close to an airport, will figure out what to do. VMC, just ensure the Alt Field and battery master are off (so have one ignition and stby att for as long as possible) and use iPad to navigate. If in IMC, still turn Alt Field and battery master off and switch to essential power bus and land as soon as possible.

This seems like the best setup to me. Always open to any thoughts or suggestions because I know there's a buch of them out there!! Thanks.