Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Dual Battery System Question
- Thread starter f1rocket
- Start date
f1rocket
Well Known Member
I'm amazed that there appears to be no one else out there using the BatteryLink product. If you are using two batteries, how are you connecting them to your alternator? What if one of your batteries goes bad, how are you isolating it so it doesn't drag down your good one?
Just FYI for those who might be wondering, the BatteryLink ACR is a device from the boating industry that controls the charging of multiple battery banks from a single alternator. All it really is are some diodes and switching circuits so you could do this yourself I suppose. You simply connect it between both batteries and it control the flow of the alternator charging current back to the battery that needs it. If one battery sinks below a selectable voltage, the device isolates that battery automatically. It is simple, fairly small, and light weight. It does cost a about $90 though. You can even use two batteries of dissimilar composition. I thought it was a neat item so I'm using it in my build but it appears others are doing something different?
Just FYI for those who might be wondering, the BatteryLink ACR is a device from the boating industry that controls the charging of multiple battery banks from a single alternator. All it really is are some diodes and switching circuits so you could do this yourself I suppose. You simply connect it between both batteries and it control the flow of the alternator charging current back to the battery that needs it. If one battery sinks below a selectable voltage, the device isolates that battery automatically. It is simple, fairly small, and light weight. It does cost a about $90 though. You can even use two batteries of dissimilar composition. I thought it was a neat item so I'm using it in my build but it appears others are doing something different?
Dual Batteries
I have two batteries and one alternator. 2 contactors and 2 master switches and an isolator to charge both batteries equally. My theory is if I have an alternator failure, I shed power, switch off one battery and start my timer. If I start to lose power on one battery before I land I switch to the other and I know how much time I have left. Like switching tanks.
If you need more detail ask.
Ken
I have two batteries and one alternator. 2 contactors and 2 master switches and an isolator to charge both batteries equally. My theory is if I have an alternator failure, I shed power, switch off one battery and start my timer. If I start to lose power on one battery before I land I switch to the other and I know how much time I have left. Like switching tanks.
If you need more detail ask.
Ken
f1rocket
Well Known Member
Thanks Ken. This is my first time at using two batteries so I like to understand how others have done it so I can learn more. In comparing your set up with mine, they are similiar but different. My system operates just like a single battery system with a single master switch so I don't have to "think" about the other battery. I have a single switch that is set to either "primary" or "auxiliary" and this switch determines which battery is driving the system. At any time and at any switch setting, the BatteryLink is charging both and/or disconnecting one or the other from the charging circuit automatically.
The only problem I see with my approach is if my battery select switch fails open so neither battery solenoid is energized. This is really no different than if a single master switch fails to energize the battery solenoid. In effect, the battery would be removed from the circuit and the alternator current would have no place to go. At this point, the alternator controller would remove alternator from the circuit and I'd have a total electrical failure. Same goes for your typical single battery system, it is the same failure point.
Your system of dual master switches provides you with redundancy that I don't have. For me, one switch takes out both batteries. For you, one switch just takes out one battery. Hmmmm, I'm going to have to think about that.
What happens if you turn both of your battery switches on at the same time?
The only problem I see with my approach is if my battery select switch fails open so neither battery solenoid is energized. This is really no different than if a single master switch fails to energize the battery solenoid. In effect, the battery would be removed from the circuit and the alternator current would have no place to go. At this point, the alternator controller would remove alternator from the circuit and I'd have a total electrical failure. Same goes for your typical single battery system, it is the same failure point.
Your system of dual master switches provides you with redundancy that I don't have. For me, one switch takes out both batteries. For you, one switch just takes out one battery. Hmmmm, I'm going to have to think about that.
What happens if you turn both of your battery switches on at the same time?
Capflyer
Well Known Member
Like Ken I have two contactors and two master switches. I start the engine with both batteries and the alternator only on one then after start up shut off the back-up battery switch. I also have two Lightspeed ignitions and each is connected directly to a battery so they are completely out of the loop of busses and other electrical components. Using diodes each battery is charged simultaneously. I can monitor my alternator output through the GRT EIS connected through to the EFIS and a warning light.
To me this gives ultimate redundancy and a method to determine when it's time to switch to the back-up battery.
The thought of having everything go through only one circuit scares me especially since I fly IFR.
To me this gives ultimate redundancy and a method to determine when it's time to switch to the back-up battery.
The thought of having everything go through only one circuit scares me especially since I fly IFR.
tc1234c
Well Known Member
Electric Bob's article
Randy,
I did the same as Ken and Mike. Here is an article for your reference. It is written by Bob Nuckolls on multiple battery myths:
http://www.aeroelectric.com/articles/Batteries/Multiple_Battery_Myths_A.pdf
My wiring diagrams:
http://3limafoxtrot.com/technicalinformation.htm#electrical
Randy,
I did the same as Ken and Mike. Here is an article for your reference. It is written by Bob Nuckolls on multiple battery myths:
http://www.aeroelectric.com/articles/Batteries/Multiple_Battery_Myths_A.pdf
My wiring diagrams:
http://3limafoxtrot.com/technicalinformation.htm#electrical
Last edited:
tommylewis
Well Known Member
dual battery here also
I use a dual battery with a resister and Schottky Diode (NTE 585) which was listed as a 1 amp, 40 Volt max with a drop of 0.6 volts. My resistor was a 10 Ohm. This was what Paul Dye used also and has worked well for me for 480 hours now.
I use a dual battery with a resister and Schottky Diode (NTE 585) which was listed as a 1 amp, 40 Volt max with a drop of 0.6 volts. My resistor was a 10 Ohm. This was what Paul Dye used also and has worked well for me for 480 hours now.
I have the same setup as the others two masters, two solenoids, one for Batt A one for Batt B. The article from Aeroelectric jogged my memory from 5 years ago when I designed my electrical system. I am using two standard mags so I couldn't see incorporating a secondary buss. Both batteries feed the main buss and the avionics buss. I can see operating lightspeeds off two independent busses. If I loose my alternator I still have two fully charged 680's which can run everything for 30 minutes each plus the backup batteries inside the AFS 3500's give me an additional margin for the primary flight instrumentation. One advantage to the two batteries, I can play with the avionics off one while the other remains on the charger. I'm glad Bob cleared up the charging of the batteries when connected to a single buss. There is several different views floating around out there. I conducted my own scientific experiment..kinda. I hooked the batteries up parallel, read the voltage at each pole while it was charging. Both batteries were getting the same amount of voltage and both batteries charged completely, finishing the cycle controlled by the charger. So figured I was safe with my design.
Last edited:
Mike S
Senior Curmudgeon
Mine too, and I also spent time learning/understanding how to make a setup I was happy with.
I started with a project that was 90%/90%, included dual batt, and dual alternators, but no wiring or schematic.
After a lot of studying Nuckols, and talking to local aviation guys, and more than a little design/re-design work, what I came up with is -----
Main batt (Odyssey 925) is powered directly from main alt---60a. Aux batt (Odyssey 680) is powered directly from aux alt---8a. Both systems have the normal master, field switches, and regulator setup.
The items I considered to be required for normal flight------Dual GRTs, radio, xpndr, intercom, and electronic ign are all powered directly from a buss fed from the aux power circuitry.
Everything else in the plane is powered from the main buss, and the main buss feeds to the aux through a high current Schottky diode.
In addition, I have a battery cross tie contactor that I installed to facilitate starting, if the main batt gets weak. An un-intended side effect of this is that the Aux alt is able to also charge the main batt, when the batteries are tied together.
In ground testing, all seems to work well so far. I can light up the panel from either master, and switch to the other buss with no drop out of the EFIS, or radio stack. As I havent started the engine yet, the charging side of things is yet to be proven, but it is sound in theory, so all should be fine there also.
For those who noticed that the aux buss doesnt power things like boost pump, pitot heat, flaps, lighting, autopilot, and etc, correct. I designed the system so that in the event of a main elect failure it will allow me to safely fly for an hour or two if needed, until I could find a place to land, and fix the problem.
As Stein would say, my $.02.
Hope this feeds the knowledge hunger a bit.
Good luck.
Dual Batteries
Another consideration for redundancy is the avionics master. Since I decided to not use an essential buss and just use a check list to shed power if needed, I questioned installing an avionics master as well. My friends in avionics were questioning my decision saying that I could easily damage avionics if I forgot a switch on. Anyway, they said all aircraft with significant avionics have an avionics master.
So I think, dual batteries, redundant instruments, redundant radios, and I put all this on one breaker switch! Single point of failure for the whole panel. Then when I came to install the name brand breaker switch (made in China) I could not hand tighten the nut because the threads were so undercut! Wonder what the inside could look like?
That did it. I installed a 30 amp breaker in parallel with the avionics master switch. The breaker is located under the panel in an easy to reach place with the breaker pulled. If my master switch goes bad, I reach under and push the breaker. Something to think about.
Ken
Another consideration for redundancy is the avionics master. Since I decided to not use an essential buss and just use a check list to shed power if needed, I questioned installing an avionics master as well. My friends in avionics were questioning my decision saying that I could easily damage avionics if I forgot a switch on. Anyway, they said all aircraft with significant avionics have an avionics master.
So I think, dual batteries, redundant instruments, redundant radios, and I put all this on one breaker switch! Single point of failure for the whole panel. Then when I came to install the name brand breaker switch (made in China) I could not hand tighten the nut because the threads were so undercut! Wonder what the inside could look like?
That did it. I installed a 30 amp breaker in parallel with the avionics master switch. The breaker is located under the panel in an easy to reach place with the breaker pulled. If my master switch goes bad, I reach under and push the breaker. Something to think about.
Ken
f1rocket
Well Known Member
Thany you for all the posts. It is interesting designing the electrical system, no? So many options and no one single right or wrong way to do it. Thank you for the link to the Bob N. article. I had read that before but had forgotten about it. Sometimes I have a little trouble always understanding where Bob is coming from. On one hand, he proposes hooking the batteries straight up in parallel without any other devices and then he proposes a wiring diagram with crossfeed contactors, diodes, switches, etc.
I think I understand the pros and cons of a completely duplicate battery/contactor/master switch architecture. I still haven't decided how I want to wire mine, but I think I can live with the drawbacks of my approach in exchange for simplicity, intuitiveness, and fewer parts.
I think I understand the pros and cons of a completely duplicate battery/contactor/master switch architecture. I still haven't decided how I want to wire mine, but I think I can live with the drawbacks of my approach in exchange for simplicity, intuitiveness, and fewer parts.
