Duel battery installation

[yateselden]

I am in the planning stage of changing to a duel battery set up from a single Odyssey 680. Looking at the Blue Sea systems off/on/both and their ACR (automatic charge relay). Also the Earth X battery/batteries but may use the pc680 as the backup. It doesn't have quite enough power for starting. Tho it will start, it's lazy. Q, do I need to fuse the charge wires from the ACR to the batteries? Earth x batteries have over charge protection from what I read. I have fuel injection and want reserve in case of alternator failure. Has anyone done similar?

[PaulSA]

What you do need is over-voltage protection on the alternator - mandatory from the EarthX manual. This gives you 3 levels of protection - the third being manually shutting down the ALT field.

I'm not sure if the electronics in the EarthX will react well to being tied to another battery ........

[svyolo]

I have EFI/EI and am installing 1 battery to start, but will probably add another. I will have automatic backups for 1 thing, fuel pumps, and will probably add another for 2 batteries. Bob K's logic on his circuits usually have the second battery on a diode, and a switch, in parallel. If the primary battery falls below a certain voltage, the backup kicks in automatically, or manually with a switch.

I am doing the same with the dual fuel pumps. I have a low pressure switch which turns on the backup, in parallel with another manual switch which also turns on the backup.

[JimParker256]

I don't get the whole "two batteries" thing. Batteries are either heavy and cheap, or very expensive and lightweight. A battery is a BACKUP electrical supply, except during engine start, when it's the primary. The rest of the time, it's there just to absorb "peak" loads that the alternator cannot meet. And with a properly engineered electrical system, those can be minimized or eliminated. If you're worried about an alternator failure, followed by a primary battery failure, why not install a backup alternator instead? B&C makes some nice accessory-pad mounted alternators that would be really nice. They're about the same cost as a good battery, weigh about the same, and are pretty much a "one-time" expense, versus having to check/replace the "spare" battery every annual. The secondary alternator has its voltage regulator set for 1/2 to 3/4 volts lower than the primary alternator, so it is turned on automatically (no pilot action) when/if the primary alternator fails. The idea is to reduce cockpit workload during the failure. A battery failure on the ground is a non-emergency (and easily solved with a lightweight and inexpensive "jump pack" these days). A battery failure during flight is likely to go completely unnoticed until/unless the alternator fails as well. And THAT would be a potential emergency for an all-electric (or electric-powered FI system) airplane.

[AKKen07]

I agree with you for the most part Jim, frankly, yet I am still opting for a dual battery setup. My reason is pretty simple: I wanted a backup electrical source and a brownout battery. I am setting my system up with two equal lightweight (and expensive) batteries which I can isolate during engine start using one for the starter and one for the electronics. That keeps my engine gauges protected and available even if my start battery gets a bit low prior to starting. So even though as a in flight backup it isn’t as logical as a 2nd alternator it will provide more juice than I will have fuel and give me other options that an alternator won’t prior to engine start. That’s my rationale anyway.

[Battson]

You will still need to maintain a second alternator, they take more work than a modern battery?
It will be running (rotating) all the time, so gets worn out at about the same time as your other alternator, increasing the risk of a double failure.

[Burgerilla]

Jim, I completely agree and thoroughly support each point you make here. I completely understand the other points of view expressed, but I spent many years working on Part 25 airplanes that had all these redundancies, and if someone feels they gain more reliability or safety with them, I feel they were providing me with more job security. I strongly support your comment here.

[svyolo]

I sort of went down the same logic path with respect to a second alternator and second battery. The vast majority, probably way north of 75% of alternator failures, are actually voltage regulator failures. Since I am planning on flying in mostly remote places, and my airplane needs electricity, I thought I would just carry an extra voltage regulator as a spare. But then I thought, why not just mount it, and put in on a switch? So that is what I am doing. 1 alternator, and two, switchable VR's. I get most of the redundancy of 2 alternators, with less weight and money.

Same with the battery. I thought I would carry a jump pack, to jump start if I, or somebody else needed a jump. But if I am going to carry a jump pack, why not mount it, and wire it to a switch? It can still be removed for jump starting. It will only be wired to be a "load" to stabilize the alternator output if the main battery fails.

[JimParker256]

I sort of went down the same logic path with respect to a second alternator and second battery. The vast majority, probably way north of 75% of alternator failures, are actually voltage regulator failures. Since I am planning on flying in mostly remote places, and my airplane needs electricity, I thought I would just carry an extra voltage regulator as a spare. But then I thought, why not just mount it, and put in on a switch? So that is what I am doing. 1 alternator, and two, switchable VR's. I get most of the redundancy of 2 alternators, with less weight and money.

Same with the battery. I thought I would carry a jump pack, to jump start if I, or somebody else needed a jump. But if I am going to carry a jump pack, why not mount it, and wire it to a switch? It can still be removed for jump starting. It will only be wired to be a "load" to stabilize the alternator output if the main battery fails.

Interesting approach with dual (switched) voltage regulators. I'm probably just going to use alternators with built-in regulators (B&C or – ahem – "NAPA") because they seem to be cheaper and far more reliable (when's the last time your car's voltage regulator went bad?). If both fail, well, that's why we have batteries.

But then, I'm not flying IFR, and not planning to use electronic fuel injection (though intrigued by some of the recent developments in aftermarket EFI), and the PMags I plan to use will self-sustain after starting the engine... So your mileage may vary!

[svyolo]

VAF has an "Alternator reliability poll" in the electrical section. It is a good read. It backed up my own experience with alternators - it is usually the regulator that fails. I was originally going to carry a spare. But then I thought why should I have a regulator laying around somewhere when I can mount it permanently?

I asked the B&C rep at SNF the same question, and he said the same thing. The vast majority of the time the failure is the VR.

[whee]

I am in the planning stage of changing to a duel battery set up from a single Odyssey 680. Looking at the Blue Sea systems off/on/both and their ACR (automatic charge relay). Also the Earth X battery/batteries but may use the pc680 as the backup. It doesn't have quite enough power for starting. Tho it will start, it's lazy. Q, do I need to fuse the charge wires from the ACR to the batteries? Earth x batteries have over charge protection from what I read. I have fuel injection and want reserve in case of alternator failure. Has anyone done similar?

Mine is quite similar; Dual batteries, Perko Switch, diode to isolate the batteries, single alternator.

Take a look at the reviews of the Blue Sea switch. They have a pretty good reputation for breaking; ie it’s not a matter of if but when. I chose to use a Perko switch instead.

I was going to use a Blue Sea ACR but after emailing the AeroElectric guy I decided to just install a diode. I found a diode on digiKey that works great. Alternator is feeding the diode which then feeds both batteries. ACR would work too but this was simpler, light, cheaper. I can’t remember for sure but some ACRs combine the batteries and some keep them isolated. If you want to use one 680 and one earthX it might be a good idea to keep the isolated. But maybe it doesn’t matter, IDK. My diode maintains isolation of the batteries.

I did not install a fuse in the change circuit but I think installing one is a beat practice.

[Bdflies]

There are lots of IFR Certified electrically dependent airplanes out there. How do Piper, Cessna, Beech and Mooney deal with this issue? I built mine as a VFR aircraft and my Emag is self sustaining, so one battery and one alternator is good for me. Frankly, I'm surprised at speculation about different approaches to electrical security. I would’ve thought this issue was settled science. What am I missing here?

Bill

[zkelley2]

I sort of went down the same logic path with respect to a second alternator and second battery. The vast majority, probably way north of 75% of alternator failures, are actually voltage regulator failures. Since I am planning on flying in mostly remote places, and my airplane needs electricity, I thought I would just carry an extra voltage regulator as a spare. But then I thought, why not just mount it, and put in on a switch? So that is what I am doing. 1 alternator, and two, switchable VR's. I get most of the redundancy of 2 alternators, with less weight and money.

Same with the battery. I thought I would carry a jump pack, to jump start if I, or somebody else needed a jump. But if I am going to carry a jump pack, why not mount it, and wire it to a switch? It can still be removed for jump starting. It will only be wired to be a "load" to stabilize the alternator output if the main battery fails.

Because with a jump pack like an XPS you can do a lot more than just power your airplane with it.

We did a real long range trip once and stashed 50 gal of gas on a beach. When we went to use it we just plugged into the XPS battery to power a 8gpm fil-rite.
That XPS also kept the in reach and portable gps charged for over 2 weeks.
Then it still had the power to crank the IO-360 that was on that plane.

The model I carry is rated to jump a 7.3 Diesel.

[robcaldwell]

I decided early on that I would go with the dual Light Speed Electronic Ignition. When discussing the design and layout of my panel with Jason Smith at Aerotronics, he highly recommended a split bus system (hot bus / main bus / avionic bus) with a single alternator and dual batteries and a 3rd backup battery. His recommendation came from his close relationship with Klaus Savier, the founder of Light Speed Engineering. This is what Klaus prefers. Below are the pics of my panel and confirms why it was built this way.

I suppose you could say the independent battery switches are the same as a Perko Switch. Bill is correct that we are continually debating this electrical arrangement. Having read some of the above comments, I am wondering if I should have a backup alternator now. I'm really at the point where I wish we could reach a consensus on the subject. I'm not enjoying the continual doubting.

IMG_1823.JPG

IMG_1822.JPG

[Burgerilla]

WOW!! That is one beautiful panel, Rob!

[svyolo]

It is probably better to grab a big bucket of popcorn and some adult beverages and read the long and sometimes contentious threads on VAF. Then decide for yourself what you are comfortable with.

[yateselden]

I should have mentioned, there is no option for a second alternator. I'm running a Mazda 13B, it is shunted / amp gage installed. At this point, I'm dependent on one alternator and one battery. Im just looking to increase my odds. Thought about a booster pack but they are expensive for a good one and heavy. This subject is my extreme weak point. Maybe just add another battery on a switch and call it good. Im VFR only, the main thing is to power the EFI to where I can land safely.

[svyolo]

Whatever kind of 2nd battery I end up with, that is how it will be wired. I wouldn't call it a true second battery, just some extra capacity if I need it. I have been leaning toward a lithium jump pack. Mounted but removable to jump start my self, or somebody else. It won't even be set up to be charged unless it is switched on for use.

[Battson]

*imagines two batteries having a duel*

I have kept my PC680 and installed a small EarthX for a dual setup. The EarthX is only big enough for backup, not starting.

For better or worse I sometimes switch them together to start in winter - it makes a HUGE difference compared to just using one battery. I bet it's hard on the weaker / smaller of the two though. If anyone knows more about this risk, I am all ears.

I have fused the smaller battery so it is disconnected if its starting current exceeds a 10A fuse rating, which it regularly does when cold.

Just having the initial impulsive power of two batteries to get the prop swinging fast makes a difference. Having a carbon prop, I have little rotational inertia, so it has to fire first go, which it normally does.

[svyolo]

Yeah, sorry, too simple a comment. No problem with a simple, basic votlage regulator charging a lithium battery (through its BMS). Charging a lithium and lead acid in parallel with some of the features that we, or the VR manufacturers (crowbar, over voltage protection etc), might not play well together. It might be fine 99% of the time. The over voltage protection might kick in on the VR, or the BMS (this would disconnect the lithium battery).

I am not sure, and don't want to be the test pilot. If you could select the lithium and Lead acid to charge one at a time, no problem.

B&C VR's supposedly have some issue with VPX's. I can't remember what it is but I think there is a fix.

[JimParker256]

Seems like I remember reading that the EarthX folks want the VR set slightly higher for recharging their LiFePo batteries than is typically used for charging Lead Acid batteries. Combining the two might either require over-charging the Lead Acid battery or under-charging the EarthX. Not sure either one is a great idea. Probably something could be done with an in-line resistor (or something like that) to drop the voltage supplied to the Lead Acid battery. (But I am NOT an expert in this area, and would STRONGLY recommend checking the the AeroElectric Connection community before attempting to mix battery types with a single alternator/VR recharging both systems.)

[Battson]

Per my original post, I am charging a Pb and Li-X battery in parallel with no adverse affects. Hundred + hours now.

[rodsmith]

"I suppose you could say the independent battery switches are the same as a Perko Switch. Bill is correct that we are continually debating this electrical arrangement. Having read some of the above comments, I am wondering if I should have a backup alternator now. I'm really at the point where I wish we could reach a consensus on the subject. I'm not enjoying the continual doubting."

I doubt there will ever be a consensus. Each of us is designing our electrical system to meet our perceived needs. Most of us are building a much more robust, fault tolerant system than what we have flown with in certified aircraft. Beautiful job on the panel Rob.