12V batteries in Series for 24V

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Kevin Holbrook

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I have recently begun working with a hangar mate on an RV-10 project that I will likely become partner in. It is an older build with steam gauges that we are upgrading. Need to replace battery.

The electrical system is 24 volts, and changing that seems daunting.

The current battery is a Concorde RG24-16, and a new one is about $700. I have previously had PC680s in the two RV-6s I built, and I keep thinking about how well they have served me and that they cost about $130.

I am wondering about the feasibility of running two PC680s in series. About the same weight and footprint, a couple of extra amps, and less than half the cost.

Any reason not to do this?
Any thing to look out for if going this route??


All input gratefully received; would especially love to hear from @weirdjim !!!
Thanks in advance,

Kevin
 
There are several Velocities flying with Odysseys in series. Screen Shot 2019-09-20 at 11.49.45 PM.png
 

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I have that. exact setup (two PC680’s in series) for about a year now.
<<<<
Many owners of my type do as well (that’s where I got the idea, the type club)

I consider them a sensitive battery.
The charging voltage is higher. Much discussion with...Enersys? to establish how to handle them.

you can’t use just any old maintainer, $250 batteryminder..... specific for Odyssey.

there is not a ton of reserve, some panel activity, and 2-3 gear swings -and it would barely turn the prop.

The charging V is 29.5 to 30 for maintaining, and from ship’s system...in flight.
Be sure to measure the voltage the battery sees while the a/c is running ie voltmeter on the battery terminals. It is common to have a volt drop from there to your panel voltmeter. So the vom might read only 29v on your panel but your battery might actually be fine, at 29.7
You will have to tweak your vregulator upwards, to get that 29.5-30V as most are set for lead acid batteries, 28v or so.

If it is set ahead of your ewcg, the swap will worsen any aft-cg tendancy.
 
That's what's in the Beech 18. Two 12 volt batteries in series. Just regular 35 series? 12-volt aviation batteries x 2.
 
Let'sgoflying! said:
those are in series? not seeing it.
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donjohnston said:
Yeah, looks like a parallel install to me.
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That's what I thought too. But maybe one is a RH battery and one a LH. Can't see any + or - stamps but noticed the PC680 labels are on opposite sides. If series, it looks like it's being tapped both 12v & 24v.
 
timwinters said:
That's what I thought too. But maybe one is a RH battery and one a LH. Can't see any + or - stamps but noticed the PC680 labels are on opposite sides. If series, it looks like it's being tapped both 12v & 24v.
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The two terminals on the right are red, and the two on the left are black. Also the larger cables on the right are marked + and the left is marked -

I find that wiring very odd, but there’s no way it’s series.
 
odysseys need special voltage and special maintainers? Why? Is that a 24v thing?
 
The batteries look wired as separate 14 volt circuits...I cannot tell where the positive cables are going. If they are both connected to the battery relay, I suppose this was a parallel arrangement in order to double the cold cranking amps..maybe?
 
Capt. Geoffrey Thorpe said:
Bolted one into my ride, nothing special anywhere. Don't use a maintainer since it rarely sits more than 6 months without flying (and spins right up after 6 months).
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I’ve had one in my 180 for 20 years. Same pirep. When this one quits I’ll switch to EarthX. Now THAT one is a little more sensitive to charging but both planes use B&C alternators-regulators so no worries on my part.
 
Doug Reid said:
The batteries look wired as separate 14 volt circuits...I cannot tell where the positive cables are going. If they are both connected to the battery relay, I suppose this was a parallel arrangement in order to double the cold cranking amps..maybe?
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Looks like a starter battery and a house power battery style arrangement.
 
But in any case, the nominal voltage for a lead acid cell is about 2 volts. If you want a 6 volt battery, you put three cells in series. For a 12 volt battery you put 6 cells in series. For 24, it's 12 cells. It doesn't matter if the cells are all in one case or divided between 2 or more boxes.
 
99% of the underground equipment I work on is 24v. 2, 12v, 4D batteries they weigh about 100lbs each. Not fun to change out climbing up 8 feet to install. Alternators are 120amp. Some of the alternators are even water cooled, $3,500 each.

Good eye @Let'sgoflying!
 
Doug Reid said:
The batteries look wired as separate 14 volt circuits...I cannot tell where the positive cables are going. If they are both connected to the battery relay, I suppose this was a parallel arrangement in order to double the cold cranking amps..maybe?
Click to expand...
That would be my guess.
 
That's the way my Caterpillar is wired up for 24 volts.
Don't fly too good though.
 
Datadriver said:
There are several Velocities flying with Odysseys in series. View attachment 78035
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timwinters said:
That's what I thought too. But maybe one is a RH battery and one a LH. Can't see any + or - stamps but noticed the PC680 labels are on opposite sides. If series, it looks like it's being tapped both 12v & 24v.
Click to expand...

That's a parallel install. Don't know why it has two positives going off. Maybe just an easy way to take the power to two places. The negative terminals are on the left on both batteries, note the black kind of a star underneath the terminal post. Red on the right side means positive.

Edit: now I'm thinking the two cables are both going to the same battery master. I'm guessing that the batteries are quite a distance from the starter and the two cables are to reduce voltage loss.
 
timwinters said:
That's what I thought too. But maybe one is a RH battery and one a LH. Can't see any + or - stamps but noticed the PC680 labels are on opposite sides. If series, it looks like it's being tapped both 12v & 24v.
Click to expand...
. That’s my guess They’re taking 12v off of the top battery (left and right leads) and taking 24v off the pair (two right hand leads).

Probably a mix of 12 and 24v equipment on that bird.
 
Bill Jennings said:
. That’s my guess They’re taking 12v off of the top battery (left and right leads) and taking 24v off the pair (two right hand leads).

Probably a mix of 12 and 24v equipment on that bird.
Click to expand...

I don't think you can get 24 volts off that set up. Pretty sure in fact but I never state anything positively when it comes to electrics because that's my weakest area of mechanics.
 
alfadog said:
I don't think you can get 24 volts off that set up. Pretty sure in fact but I never state anything positively when it comes to electrics because that's my weakest area of mechanics.
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It is hard to tell, but I dint believe they are paralleled. There is a jumper on the left side, but none on the right side. Could be that the right two leads are tied together somewhere out side of the picture. Dunno.

Not enough info given lol c
 
One of those batteries might be the reserve for the glass panel, the other being the main battery. A diode setup would see that both get charged off the alternator, but the non-avionics systems would not be permitted to draw off the reserve.
 
Let'sgoflying! said:
those are in series? not seeing it.
Click to expand...

LOL. For the record this photo was taken in 2016 at the Velocity Open House. The factory had this bird all opened up and was making an engine maintenance video on it. They were also fidgeting with the panel.
 
There was discussion here about the charging voltage (either a maintainer, or ship's power).
Here is some documentation and research done by Enersys (Odyssey batteries).
Battery will last longer if charged correctly:
 

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I spent more time than I thought necessary figuring out that battery rig.

First, the two batteries were different lots or different factories, labels are quite different. Otherwise, the are electrically the same. As previously noted, the plastic around the terminals are red on the right, and black on the left, so the polarity of each is the same.

The plus cables on the right are different guage, and the heavy one should be the cranking battery, the smaller one, the panel electric supply. This keeps the voltage surges and inductive spikes from the starter from reaching the electronics. In the modern world, a very desirable feature.

The left cable is the same size as the cranking cable, and is the common for both loads. Since the electronics are usually not on until the engine is started, there is no problem with the shared cable.

The system is definitely 12 volt, and as has been said, the charging circuit will have diodes in it to charge from one alternator, but be isolated otherwise.
 
Think youll be happier in the long run if you just get a 24v batter vs all this nonsense.
 
Yes, because you need 14V to charge a 12V battery so your equipment better be able to operate over that range (and perhaps a little less volts as well).
 
kgruber said:
The system will be 14V, or 28V.
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Well, we like to call lead-acid chemistry batteries "two volt nominal" per cell, hence the 12 and 24. Only aircraft call the systems by 14/28 (which is a little closer to reality).
 
I’ve seen a 12V to 24V aircraft inverter for sale, used. I think it originally came from Aircraft Spruce. The conversion will consume power; but you could have 24V equipment on a 12V system. But aren’t most avionics 12 or 24 V capable already?
 
I have two PC680’s in the venture in series for 5 years now with no problems. They don’t quite have the cranking amps when cold I’d like but they work.
 
Crashnburn said:
I’ve seen a 12V to 24V aircraft inverter for sale, used. I think it originally came from Aircraft Spruce. The conversion will consume power; but you could have 24V equipment on a 12V system. But aren’t most avionics 12 or 24 V capable already?
Click to expand...

Most modern units are dual voltage, but many older units were one or the other.
 
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