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Electrical diagram/relays

Scott Hersha

Well Known Member
I have a question or two about the simple wiring diagram I’m working on for my RV6 build. This is going to be a simple VFR panel with a GRT Horizon 10.1, a GTR200B radio, Sandia remote transponder, 2-axis GRT autopilot. B&C 40a alternator, PC680 main battery, 5 ah SLA backup battery.

My question has to do with the use of relays, and whether or not I need a couple of them. Diagram below. There is a switched bus tie relay(BTR) that feeds secondary power to the Aux bus that will also charge the Aux battery. There is another switched relay for the Aux battery feed to the Aux bus. These wires will probably carry no more than 5 amps when charging the Aux battery, and less than 3 amps when not charging. Can I just use a toggle switch for these two runs and eliminate those two relays? There is about an 85 ohm resistance through these relays and Aux battery charging will be affected. The switches are Carling switches from Stein, and are rated for 10a @ 250 VAC, 15a @ 125 VAC. How does this translated to 14 v-dc?

I plan on keeping the avionics bus relay. The drawing is crude, and I’ll probably be adding a couple things I haven’t thought of. The main battery is forward of the firewall, Aux battery aft of FW. Main bus feed through firewall is protected by a 50a maxi fuse, and the alternator B lead wire is protected by an ANL current limiter. In the event of an alternator failure, I’ll simply open the Aux bus switch, and the SureFly will be the only thing running on the Aux battery.

Comments?

6B5488A1-B3A8-40CD-B368-294875932F03.jpg
 
I have a question or two about the simple wiring diagram I’m working on for my RV6 build. This is going to be a simple VFR panel with a GRT Horizon 10.1, a GTR200B radio, Sandia remote transponder, 2-axis GRT autopilot. B&C 40a alternator, PC680 main battery, 5 ah SLA backup battery.

My question has to do with the use of relays, and whether or not I need a couple of them. Diagram below. There is a switched bus tie relay(BTR) that feeds secondary power to the Aux bus that will also charge the Aux battery. There is another switched relay for the Aux battery feed to the Aux bus. These wires will probably carry no more than 5 amps when charging the Aux battery, and less than 3 amps when not charging. Can I just use a toggle switch for these two runs and eliminate those two relays? There is about an 85 ohm resistance through these relays and Aux battery charging will be affected. The switches are Carling switches from Stein, and are rated for 10a @ 250 VAC, 15a @ 125 VAC. How does this translated to 14 v-dc?

I plan on keeping the avionics bus relay. The drawing is crude, and I’ll probably be adding a couple things I haven’t thought of. The main battery is forward of the firewall, Aux battery aft of FW. Main bus feed through firewall is protected by a 50a maxi fuse, and the alternator B lead wire is protected by an ANL current limiter. In the event of an alternator failure, I’ll simply open the Aux bus switch, and the SureFly will be the only thing running on the Aux battery.

Comments?

View attachment 22782

I don't normally comment on other people's designs because I don't know the mission/objective and everyone makes different tradeoffs.

However, I will point out that every device (switch, fuse, relay) and it's connections are potential failure points. Adding simplicity increases reliability.

For example, the relay/switch that connects between you main bus and aux bus should be replaced by a power schottky diode. Otherwise, your aux battery will try to backfeed the entire electrical load if the main battery feed fails. This can run down your aux battery before you notice the failure and flip the switch.

VV
 
I agree with Vern. I have a very similar, very simple VFR panel. My "aux bus" is a TCW battery, which includes a diode to ensure that it's charged when the alternator is generating electrons. I have the EFIS/EIS/Surefly connected to it and the main bus, and I power that up first before engine start, and it's the last thing I turn off.

If I have a massive failure, I'll be able to navigate and watch my engine. I won't be pinging out the ads-b or talking on the radio. The pmag generators will keep the engine running. I'll land as soon as possible. No flaps. No trim. No lights.

If you chose to keep more running, you can buy a bigger TCW battery.
 
I used a Schottky diode on my RV4, and it worked fine, except that there is a voltage drop across the diode, and the Aux battery didn’t get a full charge. I think there was only supposed to be about a 1/2 volt drop, but in reality it was about a full volt. I was trying to get away from that, but your probably right - keep it simple. Maybe the B&C diodes are a little better.

Thanks.
 
I agree with Vern. I have a very similar, very simple VFR panel. My "aux bus" is a TCW battery, which includes a diode to ensure that it's charged when the alternator is generating electrons. I have the EFIS/EIS/Surefly connected to it and the main bus, and I power that up first before engine start, and it's the last thing I turn off.

If I have a massive failure, I'll be able to navigate and watch my engine. I won't be pinging out the ads-b or talking on the radio. The pmag generators will keep the engine running. I'll land as soon as possible. No flaps. No trim. No lights.

If you chose to keep more running, you can buy a bigger TCW battery.

Yep. Maybe I’ll look into the more expensive TCW. I had one of those on my RV8 and liked it.

Thanks.
 
Since your previous diode dropped one volt, it was probably a P-N diode, not a Schottky diode. What was the diode part number?
Relay contacts do not have any more resistance than toggle switch contacts.
The 85 ohms is coil resistance, not contact resistance. They are two separate circuits.
The coil resistance will have no affect on aux battery charging.
Neither one of those relays is needed, unless you desire remote control.
Like others have said, use a Schottky diode between the two buses instead of a switch or relay.
 
Consider connecting the avionics to the aux bus and doing away with the avionics bus.
The aux battery will prevent brownout during engine cranking.
Does the Sandia 165R have ADS-B Out?
 
Consider connecting the avionics to the aux bus and doing away with the avionics bus.
The aux battery will prevent brownout during engine cranking.
Does the Sandia 165R have ADS-B Out?

Looks like I’ll get a Schottky diode from B&C and not use those two relays. I have an avionics bus because I prefer to have those items not powered during engine start. My Aux bus prevents brownout of my EFIS and EIS during engine start, which will be powered by the Aux bus as well as the main bus. I don’t need my other avionics powered when starting. My ADSB in/out comes from a uAvionix Echo/GRT SafeFly compliant GPS that is fastened right on the back of the Horizon EFIS. It uses the mode C from the Sandia transponder. The SureFly ignition will be the primary user of the Aux battery. In the event of an alternator failure, I’ll isolate the Aux battery and other items on the Aux bus will likely fail due to a lower voltage it sees relative to the main bus voltage. I’m doing this preemptively with thoughts of using dual SureFly ignitions somewhere down the road and I want to provide at least one dedicated battery source.
 
Scott,

Consider giving B&C a call before placing an order; I don't think theirs is a Schottky diode. Someone else here may be able to provide a spec or part number for a suitable Schottky and potential suppliers.

Regards,
Rob
N706DR
 
Scott Hersha; post #1 said:
... The switches are Carling switches from Stein, and are rated for 10a @ 250 VAC, 15a @ 125 VAC. How does this translated to 14 v-dc?...

Bob Nuckolls has a document on that, Switch Ratings, What's it all Mean? “In a nutshell, 125 VAC ratings equate favorably and conservatively to 14 VDC ratings - as long as the switch has a healthy "snap" action… all toggle switches and most rocker switches do.”

Scott Hersha; post #8 said:
Looks like I’ll get a Schottky diode from B&C...

B&C does not sell a Schottky diode. There are many choices. DSS2x61-0045A is what I am planning. Put it on a Wakefield 401K heatsink and it's easily good for 20A on the hot side of the firewall. I connect both diodes in parallel since there are two in the case.

========================

The starter button goes to B+, not ground. Ref Cole Hersee 24021 intermittent duty contactor.

You could ask you questions on the Aeroelectric List hosted by Matronics.
.
 
Bob Nuckolls has a document on that, Switch Ratings, What's it all Mean? “In a nutshell, 125 VAC ratings equate favorably and conservatively to 14 VDC ratings - as long as the switch has a healthy "snap" action… all toggle switches and most rocker switches do.”



B&C does not sell a Schottky diode. There are many choices. DSS2x61-0045A is what I am planning. Put it on a Wakefield 401K heatsink and it's easily good for 20A on the hot side of the firewall. I connect both diodes in parallel since there are two in the case.

========================

The starter button goes to B+, not ground. Ref Cole Hersee 24021 intermittent duty contactor.

You could ask you questions on the Aeroelectric List hosted by Matronics.
.

The B&C website calls it a Schottky diode, and so did the last one I bought from Mouser. Maybe it wasn’t a Schottky either. Where do I get the one you recommend? I also want the Wakefield heat sink. Mine will be on the cold side of the FW. My diagram is weak. I know that the start button triggers the +V to engage the solenoid (vs ground it). It was late and I had drawn the thing about 4 times, so mistakes were made……. again. Thanks for answering my questions, and I hope to find a suitable diode.

Thanks,
-S
 
The DSS2X61-0045A Schottky diodes are on back order at the electronic suppliers that I searched.
However, both new and used ones are available on eBay.
 
Wow!! I found that diode on a few sites online and the lead time (Mouser, digikey, outsource) has long lead times - over a year. There’s one source that has used ones with shorter lead times, but I don’t want to buy someone else’s problems. Guess I have to rethink this whole thing.

The part number you mentioned and I looked up looks exactly like the one I bought from Mouser (or Digikey) for my RV8 3+ years ago and has performed fine, except for the voltage drop, which may not have been a full volt, but was at least .75 volt. Guess I’ll just have to live with that, if I can find one.
 
Scott Hersha; post #11 said:
The B&C website calls it a Schottky diode...
-S

Sorry but B&C does not call theirs a Schottky but simply Essential Bus Diode. The latest Z schematic, Z101, calls it NTE53016 or equivalent, it’s a silicone diode bridge rectifier commonly used in home appliances that Bob Nuckolls specifies because it’s low cost, easily available, easy to mount, compatible with a heat sink, electrically isolated case. Expect voltage drop ~1.1
.
 
Sorry but B&C does not call theirs a Schottky but simply Essential Bus Diode. The latest Z schematic, Z101, calls it NTE53016 or equivalent, it’s a silicone diode bridge rectifier commonly used in home appliances that Bob Nuckolls specifies because it’s low cost, easily available, easy to mount, compatible with a heat sink, electrically isolated case. Expect voltage drop ~1.1
.

Yep, you’re right. I thought it was a schottky, and that’s what I searched, but it’s not. However the one I bought from Digikey, or Mouser for my last RV8 said it was a schottky, and it looked identical to the one spelled out above. Unfortunately, it’s not available for more than a year. I’ll be ready to fly in 2 months. I might just buy a used one on eBay. It still drops the voltage a measurable amount.
 
I used a Schottky diode on my RV4, and it worked fine, except that there is a voltage drop across the diode, and the Aux battery didn’t get a full charge. I think there was only supposed to be about a 1/2 volt drop, but in reality it was about a full volt. I was trying to get away from that, but your probably right - keep it simple. Maybe the B&C diodes are a little better.

Thanks.

The diode I use is the V30100S-E3. Rated for 30A, 100V. Right tradeoff between forward voltage drop and reverse leakage. About 0.5V drop at 10A and 0.2V at 1A. That will bring a lead-acid backup battery to close to full charge.

I use a BP1.2-12-T1 battery for the ignition bus. It's only good for 1.2A-hr (single ignition), but you may want more. My EFIS has it's own backup battery.

Parts are from DigiKey.

VV
 
DSS2x61-0045A

Newark says they will have 43 each DSS2x61-0045A arriving on 5/18 and they have the 401K heat sink. Looks like you can back order and they reserve it.

You need a dab of thermal paste between diode and heat sink, local computer repair shop or hobbyist will have it.
.
 
863-MBRF20L45CTG is suitable for powering a device from two power sources.
$1.66 each. It will drop 0.4 volts when conducting 5 amps.
 
Thank you all. I’ve found the MBRF diodes and the Vishay ones in stock, and they are cheap - 1.66 & 1.79 - but they are both surface mounted I think (through hole mounting style). I suppose they would need to be soldered to some sort of perf board. Not sure how I would mount a heat sink to that, or how I would use it in my configuration. The IXYS diode is will be available at Newark, as previously mentioned, in a about three months. So I’ll back order it. I should be flying before then, so I’ll connect the two busses with a toggle switch for now. I realize that in the event of an alternator failure, my Aux battery will feed the main bus if the main battery voltage is lower. However, an alternator failure would be indicated by a drop in voltage right away, which will be annunciated. The procedure will be to open the Aux battery/buss switch. That will isolate the Aux battery to the SureFly, which is the goal. The IXYS diode is the one I used on my RV8. There are actually 2 diodes on that one, and it mounts with screws to the heat sink.
 
Here's how I mounted mine. The two breakers are for the coils and controller of my Electroair ignition.

VV

BKR_0002.JPG
 
Here's how I mounted mine. The two breakers are for the coils and controller of my Electroair ignition.

VV

View attachment 22854

It looks like the two legs of the diode are soldered together onto the feed wire. I thought one leg was the anode, and the other one was the cathode. It also looks like the copper bus bar on the cb’s is your heat sink. Is that right?
 
Some TO-220 devices have the metal tab with screw hole connected to one of the terminals.
I believe that the mounting tab on TO-220-3 FP case is isolated from the 3 terminals.
 
This diode uses the case (tab) as the cathode and the other two terminals as the anode. It's all in the datasheet.

This is why I use it. it mounts directly on the essential busbar as shown. The connection from the anode pins to the master bus is short and does not need fusing. Minimal connections, minimal parts, to increase reliability.

Also, the copper bussbar provides an excellent heat sink. I like things that are multipurpose.

VV
 
This diode uses the case (tab) as the cathode and the other two terminals as the anode. It's all in the datasheet.

This is why I use it. it mounts directly on the essential busbar as shown. The connection from the anode pins to the master bus is short and does not need fusing. Minimal connections, minimal parts, to increase reliability.

Also, the copper bussbar provides an excellent heat sink. I like things that are multipurpose.

VV

That makes sense. Nice compact installation.
Thanks Vern
 
DSS2X121-0045B are available

snipped
My question has to do with the use of relays, and whether or not I need a couple of them. Diagram below. There is a switched bus tie relay(BTR) that feeds secondary power to the Aux bus that will also charge the Aux battery. There is another switched relay for the Aux battery feed to the Aux bus. These wires will probably carry no more than 5 amps when charging the Aux battery, and less than 3 amps when not charging. Can I just use a toggle switch for these two runs and eliminate those two relays?

Scott,
Bob N's basic rule of thumb is that any circuit which carries over 5 amps, should use a relay. Since your circuits won't, you don't need the relays.
FYI, you can get a brand new IXYS brand DSS2X121-0045B Schottky diode
at the links below:

https://www.ebay.com/itm/284612298033

https://www.ebay.com/itm/203793825459

I've purchase quite a few items from eBay members in China and Hong Kong. Shipping is usually 10 days to 17 days [to SE Florida] when paying with PayPal. I've been happy with my purchases.

Another advantage of this unit is that it is actually two diodes in one package. So you are actually carrying around a spare, if it dies away from home. Just switch the wires to the two unused terminals. PM me with your email address and I can send you the Product Data Sheet for it.
 
Last edited:
This diode uses the case (tab) as the cathode and the other two terminals as the anode. It's all in the datasheet.

This is why I use it. it mounts directly on the essential busbar as shown. The connection from the anode pins to the master bus is short and does not need fusing. Minimal connections, minimal parts, to increase reliability.

Also, the copper bussbar provides an excellent heat sink. I like things that are multipurpose.

VV

I suggest you rethink this. Those two tabs are very fragile, and your mounting will most likely result in fatigue failure.

There a very nice heat sinks that can be used such that the associated wiring can be secured. Making the leads longer helps as well. For example instead of soldering one wire across the tabs you can use a female molex connector, one for each, each having a output wire. The wires anchored close the diode package to eliminte relataive motion between the diode package on these short runs of wire.

Carl
 
Scott,
Bob N's basic rule of thumb is that any circuit which carries over 5 amps, should use a relay. Since your circuits won't, you don't need the relays.
FYI, you can get a brand new IXYS brand DSS2X121-0045B Schottky diode
at the links below:

https://www.ebay.com/itm/284612298033

https://www.ebay.com/itm/203793825459

I've purchase quite a few items from eBay members in China and Hong Kong. Shipping is usually 10 days to 17 days [to SE Florida] when paying with PayPal. I've been happy with my purchases.

Another advantage of this unit is that it is actually two diodes in one package. So you are actually carrying around a spare, if it dies away from home. Just switch the wires to the two unused terminals. PM me with your email address and I can send you the Product Data Sheet for it.

Charlie,
Thank you for that information. I did download the data sheet for that diode, and in fact that’s the one I used on my last RV8. As you said, I don’t need relays for this Aux bus power, since the normal load will be no more than 2 amps, so I’ll just use a toggle switch to tie the two busses. No need for the diode in this installation like I originally thought.
 
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