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ANL fuses?

RV7ForMe

Well Known Member
Hey there. I have looked at old post and read a bunch about the FWF big wires and stuff. Where to put the shunt and what not...

I understand people have opinions on weather or not to use an ANL fuse. But the ones who doe use one on the B lead that is actually a bit larger than the max rated output of the Alternator.... at least I read that a few time.

lets say its a 60AMP PlanePower Alt. on the RV14 the B lead seems to go straigh to the panel and the wire from the from the batt contactor also meets it there...

If I put them in line together with one ANL that means if the ALT produces to much energy the battery will also be disconnected when the fuse blows...

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If I put them in parallel and one ANL on each I would have to put a bigger one on the battery than on the ALT or they will likely both blow at the same time??

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What do you think? I understand that I am asking for opinions here.
 
My thinking is that an ANL should protect the B lead , so mounted before the shunt and any other connection to the buss or battery.
If you remote mount the battery in the back, you could mount another ANL near it to protect the long Pos Battery lead.
If you mount the battery on the firewall & have the mast solenoid close by, it’s debatable if you really need an ANL between them, I wouldn’t bother.
Placing an ANL between the mast solenoid and buss offers no protection to the circuit if a problem happens anywhere up stream of that fuse.
The job of the ANL fuses is to protect the cables leading up to the buss, not the buss it’s self. If you wish to protect the buss from over voltage events, there are various devices you can get for that protection.
 
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My thinking is that an ANL should protect the B lead , so mounted before the shunt and any other connection to the buss or battery.
If you remote mount the battery in the back, you could mount another ANL near it to protect the long Pos Battery lead.
If you mount the battery on the firewall & have the mast solenoid close by, it’s debatable if you really need an ANL between them, I wouldn’t bother.
Placing an ANL between the mast solenoid and buss offers no protection to the circuit if a problem happens anywhere up stream of that fuse.
The job of the ANL fuses is to protect the cables leading up to the buss, not the buss it’s self. If you wish to protect the buss from over voltage events, there are various devices you can get for that protection.

Thanks for your input Ralph.

I guess my train of though was that this way in the event of a short there would not be a hot cable going past the firewall. Also I realized I had the picasso drawing missing the ANL on the B lead on the one drawing.... I added that.
 
Shunt in that location will show battery state only, how many amps it is accepting when re-charging, or how many amps it is discharging if alternator is off or off line. Most of the time after the battery is recharged, it will likely show nothing, or close to ‘0’.
If you put it between the 70a ANL fuse and battery contractor, it will show the alternator output, more dynamic indication & shows your normal operating load - this is the more common shunt installation location, better for monitoring your charging system health.
You could also put the shunt between the battery contractor & buss but would only show your operating load & not give you any indication of the health of your alternator or battery
 
Shunt in that location will show battery state only, how many amps it is accepting when re-charging, or how many amps it is discharging if alternator is off or off line. Most of the time after the battery is recharged, it will likely show nothing, or close to ‘0’.
If you put it between the 70a ANL fuse and battery contractor, it will show the alternator output, more dynamic indication & shows your normal operating load - this is the more common shunt installation location, better for monitoring your charging system health.
You could also put the shunt between the battery contractor & buss but would only show your operating load & not give you any indication of the health of your alternator or battery

I have been going back and forth on this. I read the Wiring guide by mark ausmann and it claims that the alternator health can easily determined by the Volt data. 12,x means not working 14,x working. Or is there more to it?

What else am I seeing by putting it on the p lead? it will tell me the output of the alternator (what my bus is using + what the battery is taking. No way of knowing when the battery is full)
at the battery I will see the health / charging level of my battery. This I would otherwise not know. correct?

I guess I am not entirely shure what I "need" my last Cessna had it on the battery...Doesn't mean it's the way it should be.

I guess I could do both.
 
What Ralph said...

In addition, the ANL fuses should be less than six inches from the contactor.
 

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What Ralph said...

In addition, the ANL fuses should be less than six inches from the contactor.

Alright they will be since I will have it all right next each other on the Firewall.

So if I were to do it like this. do both take a 70AMP ANL? wouldnt they both blow at the same time? in that case the panel goes dark. Would it make sense to put 70AMP on the B lead and something higher 80, 90 or 100 on the in front of the bus? This way the alt is off but the battery keeps working and the panel stays on until its out of juice...

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For some reason I am always assuming that the alternator has the potential to supply to much amps. is there a battery failure mode that will do it as well?
 
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No, the alternator cannot supply too much amps. It can supply up to it’s rated output and then a bit more sometimes. It can supply too much voltage but that is addressed another way. The thing to remember is that circuit protection (fuses, circuit breakers, etc) are there to protect a wire from burning should there be a short somewhere downstream of its location. In the case of the alternator ANL, it’s job is to protect the wire between the alternator and the battery should the alternator fail causing a short to ground. It would be out of control current flowing TO the alternator, not FROM the alternator that would burn the wire. The alternator wire itself should be sized to handle the full output of the alternator. This is why the ANL fuse is to be located near the battery.

Bevan

Alright they will be since I will have it all right next each other on the Firewall.

So if I were to do it like this. do both take a 70AMP ANL? wouldnt they both blow at the same time? in that case the panel goes dark. Would it make sense to put 70AMP on the B lead and something higher 80, 90 or 100 on the in front of the bus? This way the alt is off but the battery keeps working and the panel stays on until its out of juice...

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For some reason I am always assuming that the alternator has the potential to supply to much amps. is there a battery failure mode that will do it as well?
 
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Keep in mind, a fuse is there to protect the wire connected to it - so a high draw won’t burn up your airplane. I’ve seen my 60 amp Planepower alternator put out way over 60 amps with my (at the time) Earthex battery after a normal engine start. On that airplane, I had an 80 amp ANL protecting a 4 awg wire connecting it to my main bus. This prevented a fuse blow from interrupting a pretty much normal operation. In this installation, my ANL was just upstream, about 3” (toward the alternator) of the ammeter shunt and main bus feed.
Hope this helps.
 
Further thought on putting an ANL on the battery cable, if you do, it should be a pretty hefty one. Some starters can pull well over 100a on a cold day
 
Thanks guys,

Looks like I didn’t fully understand even with the book what the ANL actually prevent. If it’s just a shortage protection I may just do one on the P lead and that’s it. This forum is great. Thanks for the education.
 
Thanks guys,

Looks like I didn’t fully understand even with the book what the ANL actually prevent. If it’s just a shortage protection I may just do one on the P lead and that’s it. This forum is great. Thanks for the education.

Think about that poor wire routed alongside a hot vibrating engine. If the insulation wears through to metal, the battery will try to discharge through that short. The ANL melts and stops the electron flow very quickly. All you see in the cockpit is a benign alternator failure.

BTW, that's an alternator B lead. A P-lead is a magneto ground, and the term is often borrowed for EI on-off control.
 
Further thought on putting an ANL on the battery cable, if you do, it should be a pretty hefty one. Some starters can pull well over 100a on a cold day
I would expect a starter to pull more than 100A turning a warm engine on a comfortable day.
A cold engine on a cold day will likely be 200 to 300+ amps to initially get the engine moving (the point of max mechanical resistance). If you throw in a high compression ratio then it increases again.
On that basis I would not expect any value of fuse meaningful to safety to last very long in a starter circuit. One that would last would need to be so huge that it would never blow in a circumstance one would need it to.

Additionally, the higher the current the greater effect of resistance in the cable, thus reducing the available voltage at the starter (Ohms Law). Each additional connection in the line will introduce more resistance, as would the fuse itself.

Fuses in battery to starter cables? Not a practical idea!
 
I used a 80 amp ANL in the B lead with a shunt. No other ANL or shunt.
Extreme care was taken with the routing and protection of the wire feeding the fuse block on the the side of the firewall.
 
The fat wire going from the starter relay to the starter motor - the one that may see 200-300 amps, or more, during engine start - typically is not fused. It is only used for a short period of time during the start sequence. After that it’s just along for the ride and sees no current until you try to start the engine again. That wire is probably 2 or 4 awg on most airplanes, depending on where the battery and starter relay are mounted, and what kind of starter you have.
 
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Per Nuckolls schematics:
1. 8AWG direct from battery contactor to cockpit fuse block: wire not fused
2. starter contactor to alternator 6AWG: slow blow ANL40 blade type fuse
 
I would expect a starter to pull more than 100A turning a warm engine on a comfortable day.
A cold engine on a cold day will likely be 200 to 300+ amps to initially get the engine moving (the point of max mechanical resistance). If you throw in a high compression ratio then it increases again.
On that basis I would not expect any value of fuse meaningful to safety to last very long in a starter circuit. One that would last would need to be so huge that it would never blow in a circumstance one would need it to.

Additionally, the higher the current the greater effect of resistance in the cable, thus reducing the available voltage at the starter (Ohms Law). Each additional connection in the line will introduce more resistance, as would the fuse itself.

Fuses in battery to starter cables? Not a practical idea!

I actually never intended to put any ANL on the starter. But thanks for the explanation. I was wondering about putting one on the battery contactor to fuse block into the cabin.
 
I actually never intended to put any ANL on the starter. But thanks for the explanation. I was wondering about putting one on the battery contactor to fuse block into the cabin.

I put one on my bus feed and my alt. B-lead. Many people agree with this approach and many people don't. Seems there has never been an agreement on this one. Is it necessary? Probably not. Does it hurt anything? Not that I have ever heard. One more point of failure is all and I have never heard of this "failing". I'm also not worried about it because almost all modern avionics have backup batteries inside the cabin anyways.
 
I was wondering about putting one on the battery contactor to fuse block into the cabin.

You can, or make one ANL serve both tasks (see below). Depends on what you're willing to lose if a single fault took down both alternator output and main bus power.

In my case, the the EFIS has its own backup power, the GPS has an internal battery, and the ignitions are battery-direct. A popped ANL is a low probability event, and not a problem when VFR.
.
 

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Thank you!

Thanks guys. Great info.

I think since this panel has only a backup battery on the G5 it would be wise to install it in a manner that a short does not take out all the lights.

70AMP ANL on the Alternator before the shunt.

Or I can tinker about a backup battery... haha
 
What sortware

OK I should have prop drawn it up nicely from the beginning...
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RV7ForMe- can you tell me what software you used to produce this schematic? I have all of my electrical diagrams drawn in pencil and I would like to make them permanent and more professional looking, but I have not found a easy to use software to do it with. Your example looks clear and very professional.

Thanks
 
RV7ForMe- can you tell me what software you used to produce this schematic? I have all of my electrical diagrams drawn in pencil and I would like to make them permanent and more professional looking, but I have not found a easy to use software to do it with. Your example looks clear and very professional.

Thanks

Sure thing. But actually I asked the same question a few times and could not come up with a good answer so I improvised.

this works for me:

Software is Free and called EasyEDA. made to do PCBs that I have done.
then I just inserted pictures of the things the programm didn't have.
Like the Alternator and stuff is just pics I took of the internet. and croped them to shape. But you may download mine Click here !

the app does great PDF exports so I am quite happy with it.
 
Is it OK to have that 100 amp shunt between the battery and the starter? What happens to the shunt when your starter pulls 200 to 300 cranking amps?
 
I have been researching the need for ANL fuses and I’m still not sure if they are required or not. In my application, I’m using an aft mounted battery in an RV4. I’m running a Dynon panel with a VP-X Sport system. Denso alternator.

Do I need an ANL fuse? If so, what size and where should it be located?

Cheers, Tom S
 
You need one ANL (or other brand) fuse located at the starter contactor.
This fuse should NOT carry starter current, only current from the alternator.
The fuse should be big enough so that it will carry 10 percent more current than the alternator rated output.
The purpose of this fuse is to protect the electrical system from a shorted alternator or its shorted "B" lead.
See Bob Nuckolls' diagram.
The output of an alternator is self current limiting. It can not put out much more than its rated output.
 
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Thanks Joe, makes sense. Would a circuit breaker not provide similar protection?
Still not totally clear.

Cheers, Tom
 
Thanks Joe, makes sense. Would a circuit breaker not provide similar protection?
Still not totally clear.
This is similar to a question I have, that being, is an ANL Fuse/Current Limiter an acceptable alternative to a conventional high current CB?

George
 
You can use either one. I prefer fuses because they are the weak link in the
circuit and will not fail to open when overloaded. Circuit breakers are mechanical
devices that can fail. I had a circuit breaker that smoked instead of opening.
 
This is similar to a question I have, that being, is an ANL Fuse/Current Limiter an acceptable alternative to a conventional high current CB?

George

Circuit breakers are faster than fuses and a lot faster than ANLs. Aeroelectric Bob has said that an ANL is capable of carrying a significantly higher than rated load indefinitely. He recommends the same rating as the alternator. Beware using circuit protection device that will carry more than the wire that it is protecting. Then the wire becomes the fuse.

Most of the time, the wire from contactor to buss isn't fuse protected. The thinking is that opening the contactor is what protects it if the pilot smells smoke. Once again, don't put a bigger fuse there than the size of the wire warrants. It won't keep the wire from burning if it shorts.

Some folks think that they need a ton of amps available at the panel. I've got two 10" EFIS and they pull something over 3A each plus a couple of amps for radios and Xpdr. LED landing and position lights for about another 6A or 9A when I'm not wig/wagging. Pitot heat would be a biggie, but there's no way I can pull anywhere near the 70A that the OP was proposing for an ANL to the panel. A big fuse requires a big wire. I count on careful wire routing and opening the contactor, not a fuse.

Ed Holyoke
 
Another reason to use an ANL is to have the fuse located next to the battery contactor. If you use a high-current circuit breaker you must run a large wire through the firewall to the circuit breaker, then back through the firewall to the alternator (in the case of the alternator B lead). :)
 
You can, or make one ANL serve both tasks (see below). Depends on what you're willing to lose if a single fault took down both alternator output and main bus power.

In my case, the the EFIS has its own backup power, the GPS has an internal battery, and the ignitions are battery-direct. A popped ANL is a low probability event, and not a problem when VFR.
.

Caution: Rookie seeking to learn asking a (dumb?) question ...

Dan (or others),
With reference to Dan’s drawing attached, is there benefit (or risk) in taking the B lead through an ANL directly to the buss rather than to the master contactor ? I see:

+ Failure of either battery or alternator buss feed ANL (or wire) doesn’t result in losing power to the buss from both Battery and Alternator. This assumes the alternator/regulator can maintain stability without the battery in circuit. It looks to me like in Dan’s architecture, failure of the B-lead results in loss of power on the buss - Alt is grounded and the battery takes out the ANL (as designed).
- Two ANLs/wires available to fail (and both must penetrate the firewall)
- Additional weight (more wire)

Any other important considerations ?

Thanks,
Peter
 

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The drawing that you attached has a risk. If the alternator shorts out and blows the
ANL fuse, then the whole electrical system fails (no battery backup).
500 RV-12s are flying with the alternator output connected to the main power bus through a fuse.
 
The drawing that you attached has a risk. If the alternator shorts out and blows the
ANL fuse, then the whole electrical system fails (no battery backup).
500 RV-12s are flying with the alternator output connected to the main power bus through a fuse.

Not sure what drawing you are referring to?
 
What I ended up doing for anyone who may read this later...

Alright guys. thanks for all the help. I wanted to take a minute and tell you what I ended up doing and why. The thread took a bit of a drift that was not my intention. For some reason some people kept taking about an ANL on the Starter wire. THAT WAS NEVER my intention and makes very little sense.

Anyway This is what I did on the RV14.
Please note that based on Dan's suggestion to keep the ANL and Shunt close to the contactors, I actually used brass bars, so they are directly connected to them.

I decided the ANL fuse on the B lead of the Alternator. Should that short out. The rest of the ship will be isolated and still run on the battery.

I decided against another ANL fuse between the Bus bar and the battery contactor.

I decided to use a Battery Shunt instead of the Alternator Shunt.

I know most people put them on them on the Alternator but I now get a negative reading showing in AMPS that will let me know how fast my battery is being discharged. Since I set the G3X to alarm anything under 0 it will show a red BATTERY AMPS if the alternator no longer supplies power to the battery. I also have a separate warning light for the alternator. If the alternator is off I will see how many amps I am actually using from the battery and can use this information to shed the load by pulling CB's.
While the battery is charging I will get a positive reading.
I will also see a 0 AMP reading when my battery is fully charged so I know that my battery is happy and healthy.

Of course YMMV but this what experimental aviation is all about.

download
 
Almost same thing

Alright guys. thanks for all the help. I wanted to take a minute and tell you what I ended up doing and why. The thread took a bit of a drift that was not my intention. For some reason some people kept taking about an ANL on the Starter wire. THAT WAS NEVER my intention and makes very little sense.

Anyway This is what I did on the RV14.
Please note that based on Dan's suggestion to keep the ANL and Shunt close to the contactors, I actually used brass bars, so they are directly connected to them.

I decided the ANL fuse on the B lead of the Alternator. Should that short out. The rest of the ship will be isolated and still run on the battery.

I decided against another ANL fuse between the Bus bar and the battery contactor.

I decided to use a Battery Shunt instead of the Alternator Shunt.

I know most people put them on them on the Alternator but I now get a negative reading showing in AMPS that will let me know how fast my battery is being discharged. Since I set the G3X to alarm anything under 0 it will show a red BATTERY AMPS if the alternator no longer supplies power to the battery. I also have a separate warning light for the alternator. If the alternator is off I will see how many amps I am actually using from the battery and can use this information to shed the load by pulling CB's.
While the battery is charging I will get a positive reading.
I will also see a 0 AMP reading when my battery is fully charged so I know that my battery is happy and healthy.

Of course YMMV but this what experimental aviation is all about.

i did almost the same thing except my main bus ANL is right before it goes in the cockpit. So my starter current does not go thru the battery Shunt. All this stuff on the firewall is close together, so there are no long runs of unfused Bus wire. And all the wires that go into the cockpit are fused to prevent the possibility of smoke in the cockpit from an unfused power wire short. here is my schematic and a picture of the firewall. I havent finished with the sealer/firestuff, so it is not ready for flight.
 

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i did almost the same thing except my main bus ANL is right before it goes in the cockpit. So my starter current does not go thru the battery ANL.

Actually that's a great Idea. You think the Garmin Shunt will burn out with the starter? Man I thought I had this done.... thanks for sharing.
 
I think it would be better to fabricate a fusible link rather than an ANL as the likelihood of finding an ANL fuse on a X/C trip would be slim to none unless you are carrying a spare.
 
I think it would be better to fabricate a fusible link rather than an ANL as the likelihood of finding an ANL fuse on a X/C trip would be slim to none unless you are carrying a spare.

Bob. The starter will not pull through the ANL but through the Shunt.
ANL on the B lead
Shunt on the battery lead
 
Anl replacement

If the anl blows on a trip and i cant find a replacement, i can use a short piece of 22 awg wire as a fusible link in the anl holder. QED

I think the fusing current for 22AWG will be right around 50A given the short run and cold temperatures. (Book value I think is 40A)
 
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If there is a boat dealer or supplier nearby, they are available through West Marine (Blue Sea).
https://www.westmarine.com/buy/blue...protected-fuses--P009_273_004_004?recordNum=2

Nearest boat place to me is 30mi away.

IMO ANL's are not worth having and can be easily replaced with a proper fabricated fusible link. Last year I replaced an alternator cable on an RV that was built in 1993 and had a piece of automotive 16ga wire as the main alternator "cable". 28 years with that **** wire. It went to a breaker in the main breaker panel, which was fine instead of an ANL. This airplane had an OV event while I was transition training the new owners and I also had to replace the alternator with a more modern one. The most typical failure mode is an OV event, not an over-current event. If the alternator cable wiring is supported correctly, the ANL or breaker or fusible link will not likely trip. Most aircraft generally have a 50A breaker.

Also keep in mind all circuit protection devices are thermal devices. They can get hot from other heat sources and trip. Winter time is when I get calls from my certificated aircraft customers wondering why circuit breakers trip that are near sources of heat.
 
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