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B&C voltage sense feed ideal location

F1R

Well Known Member
Of those people running B&C externally regulated alternators, where is your chosen point of connection for the voltage sense line that goes into the regulator.

I am chasing an intermittent overvoltage that has frustrated me to the point of Considering running a new wire and ends.

Thanks in advance for any help.
 
B&C likes the sense wire to come from the buss bar, but after talking with them, I received their blessing to install it on the switched side of the master contactor. By doing that the installation was very easy. I didn’t have to penetrate the firewall with a new wire.
 
Your comment regarding not having to penetrate the firewall for another wire tells me you may have your regulator on the engine side of the firewall. It is not recommended to be there, so be sure to plumb some cooling air to it. Those regulators run pretty hot by themselves, sometimes even very hot to the touch, when on the cabin side of the firewall. Locating them on the engine side could cause an early failure.

Vic
 
B&C likes the sense wire to come from the buss bar, but after talking with them, I received their blessing to install it on the switched side of the master contactor. By doing that the installation was very easy. I didn’t have to penetrate the firewall with a new wire.

If you do this you need some type of protection for the wire.
But I totally agree with Vic, the B&C reg should be mounted in the 'cool' cabin somewhere.
 
I am chasing an intermittent overvoltage that has frustrated me to the point of Considering running a new wire and ends.

A high resistance at any point in the voltage sense path could indeed be a cause. Intermittents are a PITA, and although I don't generally suggest component replacement based on possibility/guesswork/suspicion, this one could be an exception. If you have enough wire length and the wire visually inspects ok, you may wish to just crimp on new terminals for a start.
 
I struggled with an intermittent overvoltage (only 15 volts, usually when cold) and traced it down to a bad connection on the sense wire at the buss/CB. The bad connection increases resistance and the regulator compensates by upping the voltage due to the artificially lower voltage it is seeing through the bad connection.

Larry
 
Having previously installed their stc’d version on a Saratoga, where the regulator is installed on the firewall, I spoke with their tech regarding the placement of mine on the firewall. I fully explained my plan, which includes some ducted air and a fused sense circuit, I received their blessing.
 
Sense?? or Field?

Of those people running B&C externally regulated alternators, where is your chosen point of connection for the voltage sense line that goes into the regulator.

I am chasing an intermittent overvoltage that has frustrated me to the point of Considering running a new wire and ends.

Thanks in advance for any help.

Electricity has a supply (+) and return (-) path. The potential is between the two, the supply side might be fine, but where is the ground coming from? Does it go from battery to engine to alternator? Looking at B&C diagram it does. There are only two wired connections to the alternator B+ and Field. The ground back to the regulator has lots of connections. A silly way we all do it. :eek:

Edit: Brain fade - -I see the "sense" for remote regulator comes from bus - - but the issue could still be the ground.
 
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B&C regulators

These B&C regulators use 1970’s manufacturing technology. Perfectly good provided the regulator is kept out of a temperature cycling and vibration environment so the typical failure modes if they are exposed to that environment would be failed solder joints and cracked circuit board traces ( intermittent failures). If you have the regulator mounted on the engine side of the firewall the most likely cause of intermittent failures is inside the regulator. I took my regulators apart and added RTV to provide support for some of the more vulnerable circuit components. Not suggesting this is necessary but mounting it in the cabin area with minimum temperate cycling and away from a high vibration environment really is.

KT
 
These B&C regulators use 1970’s manufacturing technology. Perfectly good provided the regulator is kept out of a temperature cycling and vibration environment so the typical failure modes if they are exposed to that environment would be failed solder joints and cracked circuit board traces ( intermittent failures). If you have the regulator mounted on the engine side of the firewall the most likely cause of intermittent failures is inside the regulator. I took my regulators apart and added RTV to provide support for some of the more vulnerable circuit components. Not suggesting this is necessary but mounting it in the cabin area with minimum temperate cycling and away from a high vibration environment really is.

KT

From anecdotal evidence only, I would suggest that the old fashioned B&C reg will outlive the modern internal reg by a wide margin when installed in aircraft.
Probably the #1 failure of auto alternators on aircraft is the internal regulator.
 
Regulator reliability

From anecdotal evidence only, I would suggest that the old fashioned B&C reg will outlive the modern internal reg by a wide margin when installed in aircraft.
Probably the #1 failure of auto alternators on aircraft is the internal regulator.

Would agree with both arguments. Keeping electronics out of wide range temperature cycling and high vibration environments is always a good idea. At the risk of igniting the integrated versus discrete regulator debate and comparing aviation with automotive applications, OEM quality equipment always does better than aftermarket knockoff lookalikes in the same environment. Automotive applications switched over to integrated regulators for the economic, parts count, repair time, and maintainability advantages when design and manufacturability improvements allowed acceptable reliability to be achieved with a surface mount fully machine assembled internal regulator. Remotely mounted regulators will always have lower failure rates than integrated regulators for “like for like” design and manufacturing technology.
KT
 
Having previously installed their stc’d version on a Saratoga, where the regulator is installed on the firewall, I spoke with their tech regarding the placement of mine on the firewall. I fully explained my plan, which includes some ducted air and a fused sense circuit, I received their blessing.

It's just not ideal. Yes, you can duct some cooling air to it, but it will heat up after shut down, and take some time to cool after a startup, like after a fuel stop. Heat is the enemy of electronic circuits.

Many STC's aircraft originally had the regulators on the firewalls. Many of them were "point-type" regulators, with no real electronics in them. Heat didn't bother them.

When talking about installing things for reliability, minimizing heat and vibration is always a good thing. Especially since our glass cockpits now are much more reliant on electrical power.

Vic
 
Thankfully my reg is in the cockpit. And the main bus is much closer than any other temptations. It makes it sound a lot easier than it is to find the issue.
But we will report when solved. Thanks for the posts!
 
Your comment regarding not having to penetrate the firewall for another wire tells me you may have your regulator on the engine side of the firewall. It is not recommended to be there, so be sure to plumb some cooling air to it. Those regulators run pretty hot by themselves, sometimes even very hot to the touch, when on the cabin side of the firewall. Locating them on the engine side could cause an early failure.

Vic

I spoke to TJ at B&C last week about mounting locations, and he said it was "preferred" on the pilot side of the firewall because of moisture concerns (section B step 3 of the install manual). He said if mounted on the firewall, be sure to mount terminal strip side down and install proper drip loops. He said a blast tube wasn't necessary. However, I've seen LR3D regulators mounted inside the luggage compartment of -8's, only to over heat/fail when packed with bags. I tend to agree with you that heat may result in a premature failure. I'm hesitant to mount the LR3D in the luggage compartment or behind the instrument panel for service concerns. Are there other suitable locations? Perhaps on a pilot side of the instrument panel accessible through an access door? I'm wondering what the failure rate is on the firewall if mounted with proper orientation and moisture protection.
 
Here is where I mounted the regulator in the new RV-8. The panel is dual screen SkyView HDX and is fully removable in a few minutes so access is easy.
Carl
DF54-D767-BBA6-4214-8-EEB-6-C0-DCA787-CBE.jpg
 
Having been in flight and experiencing a melt down of a voltage regulator, which was mounted inside, I’ll leave mine outside.
 
Smoke and Flames

Was that a B&C regulator?

Having taken a B&C regulator apart and traced out and analyzed the circuit I came to the conclusion that if it is wired and fused according to the instructions no fire or sustained smoke is likely following a failure of any internal component in the regulator. I haven’t done any testing or other work other than looking at the FMEA ( failure modes and effects of the components) so I wouldn't say with certainty that there wouldn't be some transient smoke but a significant event is highly unlikely. This work was part of my rationale for mounting the regulators on the sub panel behind the instrument panel.
KT
 
Resolved

Electricity has a supply (+) and return (-) path. The potential is between the two, the supply side might be fine, but where is the ground coming from? Does it go from battery to engine to alternator? Looking at B&C diagram it does. There are only two wired connections to the alternator B+ and Field. The ground back to the regulator has lots of connections. A silly way we all do it. :eek:

Edit: Brain fade - -I see the "sense" for remote regulator comes from bus - - but the issue could still be the ground.

On a few investigations, I kept looking for bad ends on the sense line. A poor crimp on the VR ground wire (at the ground bus end) was found and re crimping seems to have solved the problem.

Thanks for all the suggestions. It is quite satisfying to see a steady 14.2V on a few flights now.
 
Amazing the persistent push back by some in support of mounting the regulator forward of the firewall!

In any case, one other consideration for where to mount a B&C regulator, including how and where to mount even inside the cabin is that these have an output voltage adjustment potentiometer, mounted inside below a removable plug at the top, which you are likely to want to access some time or another. Therefore you might want to mount the regulator in such a way that you can make that adjustment with the engine running.
 
Back to the topic of where to connect the sense... Its good to understand what the sense does for the voltage regulator. It senses the voltage and then compares that voltage to the reference voltage and then tries to adjust the output voltage to match the reference voltage. Now, if you connect your sense to the output of the main contactor yes it will work, but... you will be sensing the voltage there and as a result any voltage drop between that point and your bus bars or fuse panel will not be compensated for. Which means that your alternator voltage will be slightly lower than it probably should be. Is this significant maybe not but that would depend on the amount of voltage drop you have. It's always better to have "remote" sense to compensate for any voltage drops that would be in the wiring. These voltage drops vary with current since the wire resistance is fixed for a given wire size selection. Now you may say that you can just turn up the output voltage to compensate which is only partially true since again the current will vary and the resultant voltage will vary.
 
The voltage you want to regulate is the main bus or circuit breaker input. The sense point should be protected, i.e. separated from the main bus by a breaker or low current fuseable link - the sense itself draws very little current. An easy way to do this is to include the sense lead on an innocuous breaker that feeds a consistently low current load that is also relatively unlikely to go short and trip the breaker. The sense will then very closely deliver the main bus voltage to the regulator. The voltage drop across the breaker is going to be low enough to not warrant sensing with a dedicated breaker. And if you are really neurotic about it, use a fuseable link and sense directly on the main bus.
 
My Thinking

With an all electric panel, curious why the sense point needs to be at the circuit breakers. I am using a Garmin panel and I can’t think of one instrument/display/avionics that needs to have a precise voltage. In addition, the current draw from the Garmin stuff is pretty consistent and low compared to the old days of analog: even the landing light draw is greatly reduced with LEDs.
However, for long life, the battery seems to want a charge voltage that is within a few tenths of a volt, and has a current range of 30 amps or so. It seems to me, the most critical voltage to sense would be near the battery since the current fluctuation is the largest and the battery is the most sensitive to voltage variations.
What am I missing?
 
49clipper

Your comment regarding not having to penetrate the firewall for another wire tells me you may have your regulator on the engine side of the firewall. It is not recommended to be there, so be sure to plumb some cooling air to it.

Vic, That's interesting (and somewhat obvious), however I just purchased a B&C Alt and LCE regulator and ask about mounting the reg in the cabin. the guy said that would be 'nice' to have it on cabin side of Firewall, but not neccesary at all. Its made to take the heat. Straight from B&C.
 
With an all electric panel, curious why the sense point needs to be at the circuit breakers. I am using a Garmin panel and I can’t think of one instrument/display/avionics that needs to have a precise voltage. In addition, the current draw from the Garmin stuff is pretty consistent and low compared to the old days of analog: even the landing light draw is greatly reduced with LEDs.
However, for long life, the battery seems to want a charge voltage that is within a few tenths of a volt, and has a current range of 30 amps or so. It seems to me, the most critical voltage to sense would be near the battery since the current fluctuation is the largest and the battery is the most sensitive to voltage variations.
What am I missing?

Agreed, equipment doesn't need to have precise voltage, and measurement directly at the battery would be the theoretical best, and the sense point doesn't need to be at the bus/breakers. Measuring at the bus is a convenience and a minor compromise based on the assumption that the battery gets to the main bus/circuit breakers via a relatively very low resistance path and therefore delivers very close to the actual battery voltage, without having to run the sense wire through the firewall and protect it with a fuse or fuseable link there. That's assuming you mount the regulator inboard.

It continues to be surprising the persistence of the "break-it-over-your-knee-I want-to-put-the-regulator-on-the-engine-side-of-the-firewall-the-B&C-folks-said-it's-OK" view. Sure, the regulator may survive there, but again 1) Why put electronics out there unnecessarily and subject them to the temperatures and temperature cycles; 2) Makes it much harder to reach and adjust the regulator - assuming B&C; 3) Mounted Inside - One wire going out to the field connection, Mounted Outside - Field Power input, ground, O/V indicator light, O/V circuit breaker (pins 3,5,6,7) all wires going through the firewall.
 
Guess younare right

So maybe the best sense is at the bus bar since it is inside the cabin and then only the field wire goes thru the firewall. I have to think about what happens when the main fuse blows, and if the battery will over voltage. I need to know more about the B&C regulator in failure mode scenarios before deciding.
 
Agreed, equipment doesn't need to have precise voltage, and measurement directly at the battery would be the theoretical best, and the sense point doesn't need to be at the bus/breakers. Measuring at the bus is a convenience and a minor compromise based on the assumption that the battery gets to the main bus/circuit breakers via a relatively very low resistance path and therefore delivers very close to the actual battery voltage, .

Apologies for the thread drift, but on this note...
I’m wiring my RV10 and have been pondering where to run the sense as well.
On the bus is fine and nice and close to the regulators which are on the sub panel. However the batteries are down the back so about 10-12’ away and could be at a lower voltage.
As you point out, the avionics are ambivalent to 14.1 or 14.8v but the batteries are more fussy.
Should I contemplate running sense down to the back? Will I get voltage drop in the sense wire too? :eek:
Going around in circles now...
 
Richard,

No you won't get voltage drop in the sense wires. Those inputs are high impedance meaning there is very little current carried on those lines.
 
Should I contemplate running sense down to the back?

If the battery is in the back, then running a sense wire to the back may be a good idea. Just include a fuseable link right at the battery in series with the sense lead. It can be a very low current link, say 1 amp, and it is more reliable than a fuse. And concerning failure modes, if the sense opens up, which is highly unlikely, an over voltage would be recognized quickly enough by the regulator, which will then "crowbar" - short/trip the field breaker and stop the alternator from charging. BTW, there is nothing wrong with testing this kind of failure scenario as long as the battery is good and connected, as the over voltage will be short and easily limited in time and by the battery as well as the typically low OV threshold of the regulator, well within the range of most of the modern avionics.
 
If the battery is in the back, then running a sense wire to the back may be a good idea. Just include a fuseable link right at the battery in series with the sense lead. It can be a very low current link, say 1 amp, and it is more reliable than a fuse. And concerning failure modes, if the sense opens up, which is highly unlikely, an over voltage would be recognized quickly enough by the regulator, which will then "crowbar" - short/trip the field breaker and stop the alternator from charging. BTW, there is nothing wrong with testing this kind of failure scenario as long as the battery is good and connected, as the over voltage will be short and easily limited in time and by the battery as well as the typically low OV threshold of the regulator, well within the range of most of the modern avionics.

Great. Thanks for the input. Helpful
 
If the battery is in the back, then running a sense wire to the back may be a good idea. Just include a fuseable link right at the battery in series with the sense lead.

It would be silly to run a sense wire all the way to the back, the voltage drop thru the large gauge supply wire (for start current) will have an insignificant drop in normal ops.
 
It would be silly to run a sense wire all the way to the back, the voltage drop thru the large gauge supply wire (for start current) will have an insignificant drop in normal ops.


But I'd want that large gauge wire to only be live(powered) when the starter is on..............
 
Interesting thread. I was scratching my head because I didn’t remember running a voltage sense wire when I installed my voltage regulator. Turns out it’s connected directly to the alt field terminal on the regulator with a jumper. It’s been working great that way for the past 13 years. I double checked with B&C and was told that this was an approved method at that time. The only downside being that the low voltage warning light (if used) will not work. My low voltage warning is from the G3X so this is a non issue for me.
 
But I'd want that large gauge wire to only be live(powered) when the starter is on..............

So you got 2 fat wires running up front instead of 1?
I'm pretty sure the start contactor is located on the firewall for most 10's.
 
It would be silly to run a sense wire all the way to the back, the voltage drop thru the large gauge supply wire (for start current) will have an insignificant drop in normal ops.

I wouldn't label it silly without data and an understanding of what really happens. It turns out that sensing back at the battery isn't necessary and at the bus is actually a good location, but not because of the large gauge of the wire going back to the battery. The reason is that in stable operation the charging current will be pretty much exactly the same as the load current, i.e. charging current from the alternator goes directly to the loads on the bus and the current coming from the battery is close to zero, so the sensed voltage at the battery will be the same as at the bus. So, that's the steady state case.

Now, thinking about the situation after a start or for that matter a hard start or low battery, there can be significant current, say 40 or more amps going to the battery. Say you have 15 feet of number 4 going to the battery, at 45 amps that will drop .17V (or twice that if the battery is not grounded to the fuselage and a second cable is run up front), so if the regulator is set for 14.4v, the battery will see 14.23V. The consequence of not sensing at the battery then will be that it will take a bit longer to reach full charge, because the alternator will be happy to put out only the lesser current necessary to bring the bus to the regulation point, not the battery. Probably not an issue. The battery will still be charged to the regulation point.
 
I wouldn't label it silly without data and an understanding of what really happens. It turns out that sensing back at the battery isn't necessary and at the bus is actually a good location, but not because of the large gauge of the wire going back to the battery. The reason is that in stable operation the charging current will be pretty much exactly the same as the load current, i.e. charging current from the alternator goes directly to the loads on the bus and the current coming from the battery is close to zero, so the sensed voltage at the battery will be the same as at the bus. So, that's the steady state case.

Now, thinking about the situation after a start or for that matter a hard start or low battery, there can be significant current, say 40 or more amps going to the battery. Say you have 15 feet of number 4 going to the battery, at 45 amps that will drop .17V (or twice that if the battery is not grounded to the fuselage and a second cable is run up front), so if the regulator is set for 14.4v, the battery will see 14.23V. The consequence of not sensing at the battery then will be that it will take a bit longer to reach full charge, because the alternator will be happy to put out only the lesser current necessary to bring the bus to the regulation point, not the battery. Probably not an issue. The battery will still be charged to the regulation point.

The second case here is what I had in mind. Is it possible that the rapid charge at 14.2 isn’t as damaging to the battery as a permanent trickle at 14.2? We know that kills odysseys early.
 
The second case here is what I had in mind. Is it possible that the rapid charge at 14.2 isn’t as damaging to the battery as a permanent trickle at 14.2? We know that kills odysseys early.

I'm not sure under what conditions you are considering a permanent trickle.

Charging in any case will only be happening when the battery is low - say from sitting around and having lost charge, after operating electronics on the ground without the engine running without an external supply, and particularly right after a start, when a significant chunk of energy has been drawn from the battery. With the engine running, the regulator takes the sensed voltage and shoves field current into the alternator to produce whatever current is necessary to push the sense voltage back up to the regulation point, however that is set. Strictly speaking, it isn't exactly like that, as there is some elasticity built in, there are rpm and alternator capacity limits that come into play, etc. Again, steady state in flight, the battery is not charging at all - the alternator simply supplies all the load current exactly. In any case, the regulator does not see or have any direct knowledge of the alternator output current, which ultimately gets determined by the battery characteristics, specifically its effective series resistance, as well as the overall battery circuit resistance, including the cables to the battery. Lithium batteries in particular have lower internal resistance and therefore are know for higher re-charging currents after starts.

Now, if you are talking about the application of an external trickle charger for example to keep the battery full when flown infrequently, yes, steady state trickle chargers are not good for any batteries as they will lead to overcharging and generally irreversible chemical damage, reducing life expectancy. But, there are special chargers for storage applications that circumvent this with a variety of pulse and intermittent charging techniques, such as those made by a company called Battery Tender. I have one on a car I store through winter in the hanger, and it works great.
 
I'm not sure under what conditions you are considering a permanent trickle.

Charging in any case will only be happening when the battery is low - say from sitting around and having lost charge, after operating electronics on the ground without the engine running without an external supply, and particularly right after a start, when a significant chunk of energy has been drawn from the battery. With the engine running, the regulator takes the sensed voltage and shoves field current into the alternator to produce whatever current is necessary to push the sense voltage back up to the regulation point, however that is set. Strictly speaking, it isn't exactly like that, as there is some elasticity built in, there are rpm and alternator capacity limits that come into play, etc. Again, steady state in flight, the battery is not charging at all - the alternator simply supplies all the load current exactly. In any case, the regulator does not see or have any direct knowledge of the alternator output current, which ultimately gets determined by the battery characteristics, specifically its effective series resistance, as well as the overall battery circuit resistance, including the cables to the battery. Lithium batteries in particular have lower internal resistance and therefore are know for higher re-charging currents after starts.

Now, if you are talking about the application of an external trickle charger for example to keep the battery full when flown infrequently, yes, steady state trickle chargers are not good for any batteries as they will lead to overcharging and generally irreversible chemical damage, reducing life expectancy. But, there are special chargers for storage applications that circumvent this with a variety of pulse and intermittent charging techniques, such as those made by a company called Battery Tender. I have one on a car I store through winter in the hanger, and it works great.

Sorry I don’t think I worded that quite right.
When the aircraft is in flight and the alternator is supplying all the power it is still holding the bus voltage (and the battery) at 14.2 even though the battery is not drawing any charge current. Is this bad for the battery long term?
 
Sorry I don’t think I worded that quite right.
When the aircraft is in flight and the alternator is supplying all the power it is still holding the bus voltage (and the battery) at 14.2 even though the battery is not drawing any charge current. Is this bad for the battery long term?
No, the battery voltage will stay right at the regulation point. If that is 14.4V, and the battery is in the back, the battery in steady state will also be at 14.4V. The drop to 14.2V charging or so would only occur for a short while during, say heavy re-charging, and from there will climb up to the regulation set point as the charging current drops off. PM me for a phone number if you wish to discuss further.

Reinhard Metz
 
No, the battery voltage will stay right at the regulation point. If that is 14.4V, and the battery is in the back, the battery in steady state will also be at 14.4V. The drop to 14.2V charging or so would only occur for a short while during, say heavy re-charging, and from there will climb up to the regulation set point as the charging current drops off. PM me for a phone number if you wish to discuss further.

Reinhard Metz

Thanks Reinhard
 
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