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batteries in parallel

Paul 5r4

Well Known Member
I have a need for some weight forward of the CG and have decided I might as well add something useful. My current battery is an Apex and has and still is performing great but it's 5 years old. I am thinking of getting two new ones and hooking them in parallel. Is this ok and safe?

Please no suggestions of constant speed prop etc.
Thanks for your input.
 
I run a pair of PC680s in parallel on the firewall, no issues. I use the second one on the other half of the master switch, start the plane on both, switch it back off and use it as an avionics backup battery.
 
Other half of the master switch??? Can you explain. I have a cessna style master. Left is alt and right is battery. Can't switch off battery here and leave alt on.

I did find another thread where someone suggested putting in a second master solenoid so you could use one or the other. He said running them in parallel, it would be hard to know which one might be causing a problem if you can't take it offline. I liked that idea but having trouble figuring out how to wire something like this.
 
I have an old Cub with one battery and no solenoids, battery positive feeds dir to a dual 30 amp fuse block than each fuse dir to a DPDT battery master toggle, from the factory both throws fed the main bus (individually) gave you a second 30 amp fuse to power the bus if one blew. Dirt simple and never had a problem, thousands still use this original setup including me. Only time I had a 30 amp fuse pop was caused by my own accident grounding of that DPDT toggle while working on generator to Denso alternator conversion. The other pole of the battery master toggle has a jumper connecting both throws and was Gen field power, when I installed the Denso 10 years ago I cut the jumper so I could use one throw Battery only without the Alternator. A good setup, no solenoids to go bad and no issues over thousands of hours and thousands a planes still flying this way. Has no starter solenoid either, factory setup was starter is hot off the same imput to the battery side of the dual 30 amp fuse block, has a manual BIG push button starter switch with Heavy Duty contacts, like a manual finger powered start solenoid, works fine and never had an issue, the one thing you have to be careful of is the starter is ALWAYS hot, factory setup and thousands still flying today like this. The starter button is BIG and mounted under the seat from the factory, they call it the Piper anti theft switch. Works great.

So what you could do is have both batteries feeding a dual fuse block like the Piper setup except you would have a separate battery for each fuse instead of a single battery feeding both 30 amp fuses. Alternate between each battery every flight, this would give you a backup battery so you may never have a dead battery problem ever again. You would have to have two starter switches though in order to keep the batteries isolated, or a switch that breaks the connection after starting. Two good AGM batts together would really put serious AMPS to the starter though, make sure you have good brakes
 
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I have a need for some weight forward of the CG and have decided I might as well add something useful. My current battery is an Apex and has and still is performing great but it's 5 years old. I am thinking of getting two new ones and hooking them in parallel. Is this ok and safe?

Please no suggestions of constant speed prop etc.
Thanks for your input.

Nothing wrong with that approach. However, the most efficient fwd ballast is a heavier crush plate. WAY longer arm length, so less weight gives more effect. Saber makes steel crush plates in several different Weights. No harm in putting a steel crush plate on an Alum prop.

Larry
 
I have a need for some weight forward of the CG and have decided I might as well add something useful. My current battery is an Apex and has and still is performing great but it's 5 years old. I am thinking of getting two new ones and hooking them in parallel. Is this ok and safe?

Not an Apex, but I run two PC680 in parallel mounted on the firewall (RV-8). Single master switch, with an alternate emergency path if switch fails. Two starter relays control starting options for battery 1, battery 2 or both. I have charging pigtails attached to each battery individually, but have not had to use them (I fly regularly).

No issues with this setup in 350 hours, except one of the starter relays failed. A relay autopsy revealed it was likely the internal drive wire. Once I figured out this was the problem, it was a 20 minute R&R, and seemingly unrelated to the installation.
 
Yes, but...

Nothing wrong with that approach. However, the most efficient fwd ballast is a heavier crush plate. WAY longer arm length, so less weight gives more effect. Saber makes steel crush plates in several different Weights. No harm in putting a steel crush plate on an Alum prop.

Larry

No doubt it is a more "efficient" use of the additional weight for his intended purpose, but at least the second wattage source provides some additional benefit.

I'd also suggest looking at other FWF options/mods whose secondary "benefit" would be to move the CG forward: nose gear strengthening/safety mod, better performing prop, etc. There's a lot of combo's that could get the OP where he wants with some welcome secondary benefits.

My $.02.
 
Other half of the master switch??? Can you explain. I have a cessna style master. Left is alt and right is battery. Can't switch off battery here and leave alt on.

I did find another thread where someone suggested putting in a second master solenoid so you could use one or the other. He said running them in parallel, it would be hard to know which one might be causing a problem if you can't take it offline. I liked that idea but having trouble figuring out how to wire something like this.

Mine is a Cessna-style 2-switch master, two contactors. I have a separate alternator switch. This arrangement was specified by the original builder and engineered by Don Swords about 12 years ago.
 

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So MacCool. Are you saying you have a separate simple on/off type switch for the alternator and one battery contractor controlled from the 'alt' side of the master and the second battery contractor controlled from the battery side???
Seems the battery wired into the alt side would always be on and the second used as a back up? Am I thinking right? What about 2 simple on/off toggle switchs instead of the master switch. Seems then you'd be able to switch between batteries and use both 'on' for starting.

The cessna type master has that built in feature to prevent the alternator from being on and battery off. What happens if for some reason you accidentally turn both batteries to the off position and the alternator is on and running?

Sorry for so many questions. Just want to make sure I fully understand what I'm doing before getting started.
 
I wish I could tell you how it's wired, or even provide a wiring diagram, but I can't. What I know is how it works, and what both my avionics guy and the A&P who does my annual CI explained. Two contactors, one for each side of the master, and a second single-throw switch to get the alternator into the circuit.

I'm not aware that the two halves of my master switch are in any way related.
 
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I would like to think that the so called "Master Switch" in fact is of the type
that can be switched individually. No lock up between them.

Good luck
 
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