alpinestar

Hello everyone
I've got a seemingly simple problem to solve... In my new field box setup, I have two small 12v batteries. My idea is to wire the two batteries in parallel for the majority of the time,supplying plenty of 12v capacity for normal field box stuff (panel, starter, pump, etc) but have 24v available for when larger engines get stubborn & need to meet the Dynatron starter. I'd like to not have to pull the batteries, add a jumper, etc... a pair of banana receptacles on the side would be great. In my attempts of drawing the circuit capable of what I'm after I either short a battery, have uneven drain between the two batteries when using 12v, or end up with waaaay too many switches.
Any ideas from the throngs of people more knowledgable about electronics than me??
thanks!

Dr1Driver

I believe this will do what you want. That's gonna have to be a hell of a switch to handle the amps.

alpinestar

Thanks DR1! Is this an item I could find at Radio shack, or is this a more "varsity level" component than they might have?? I haven't researched the amp draw of a 12v or the 24v starter; any recommendations on what the switch should be rated for???

alpinestar

oh... one thing I noticed; this setup would supply 24V to the field box panel as well as the starter.... Any ideas how to limit the panel voltage to 12v or isolate it when using 24v power??
thanks for the help!

Dr1Driver

You could wire the power panel separately, straight from one battery. I doubt RS will have that switch. It's gonna be an industrial electrical supply shop item. Maybe something like an A/C motor reversing switch, I dunno. I have no idea how many amps a Dynatron draws when spinning a big engine. Sorry I can't help further.

Dr.1

alpinestar

thanks for the help
I might keep it simple (& cheap) by simply making a telephone-operator style assorment of banana jacks & jumpers... I won't need 24V too often & this way I can easily charge one, the other, or both.

Nice DR-1, is that from the BUSA kit??? I built the SE5a & it's turned out to be my favorite to look at & a relaxing one to fly. I have a pic in "my hanger". Got my eye on the BIG D7..... The toledo show is 3 days and only 42 miles away..

Dr1Driver

Thanks for the compliment. That's a heavily modified Flair kit. My first one was a stock Flair kit. My third one will be a Dr.1 bashed from a Flair kit using GT plans to build it.

I have more pics if you'd care to see them. Give me an e-Mail addy and I'll send you a few.

Dr.1

Hircflyer

I had the same problem....Minnflyer sent me this....works like a charm.

sfsjkid

Sullivan lists the max current at 80A.

http://www.sullivanproducts.com/StartersMainFrame.htm

This is probably a stalled condition(?), you might ask Sulluvian for clarification, or measure the current yourself. I noticed that my "normal" Hi-tork starter has the same rating, my 10A rated banana plugs, 18 gauge wire and 20A switch have lasted 4 years (this is accerated testing, as I do fly EVERY weekend). I've not stalled it (for long) but have started a Moki 2.1 with it, without ill effects so far, though I must admit, I did blow a trace on my field panel once.

I agree with DR, an 80A+ switch is going to be big and expensive, along with the proper connectors and wire. http://www.mcmaster.com/ will probably have what you'll need, albeit on the expensive side. From my experience, the gut feeling is that as long as you stay within Sullivan's operational cycle, you'll be ok, though admittedly you wil be setting yourself for a failure in the long run. Keep in mind that I run 12V exclusively. My back won't handle 2 gel-cells, so anything over say a 1.2 usually gets a hand prime, hot glow and a strong backflip, which works 90% of the time. I'll call you for the other 10%

Good luck!

Deadeye

I had the same problem. Here is what I did. Wired the batteries in parallel for 24 volts. Using the alligator clips on the Dynatron, clamp thge negative on the negative post on one battery, the positive on the positive of the other battery. There's the 24 volts for the Dynatron. I then simply clamped the power panel clips to one battery only, supplying 12 volts to the power panel. Simple, cheap, and no switches.

rcfury

My Feedback: (5)

You could just wire the batterys in parellel so the charger and panel have 12v. Then on a seperate pair of bananna plugs (female end) have those wired for your 24v. Almost to what deadeye had described but instead of using the alagator clips your plugging the starter into a bananna plug for a "cleaner" look.

alpinestar

having the batteries wired parallel & provision for 24V (series) at the same time shorts out both batteries.... I drew this on paper & that's when I realized this was a lot more complicated than I thought!!! Connecting the panel to one battery for 12v & wiring the batteries in series for 24v would work, but since I'll use 12v most of the time I was hoping to keep the two batteries balanced. I'm using two of the small 4.5 amp/hr batteries, not the normal 7 amp/hr size 'cause the two smaller ones fit inside the battery compartment of my box (GP master caddy)

Deadeye

I attached this diagram. It isn't MinnFlyer quality, but you get the idea.

liam_irish

I am thinking about using this setup in my Great Planes Master Caddy. I will be installing the 24v female banana plugs on the outside of the battery box, probably on the side so as not to interfere with the 12v power panel on the front. This 24v source will be used for my Dynatron starter when starting gas engines, while my 12v power panel will still be used for glow planes. My question is how do I go about charging both of these batteries once they are enclosed in the starter box? With the single 12v battery I currently have, I simply plug my charger (banana plugs) into the existing power panel. Would I get a second 12v charger and plug that into my new 24v output on the side of the box to charge the second battery?

Any advice/diagrams are appreciated!

Thanks,

Liam

Boomerang1

Don't use a switch, just run both batteries to two sets of large connections on the side
of your flight box to accommodate the large clips on the big starters but shielded so they
don't short. If you already have banana connections just use those.

Join them with the red jumpers for 12 volt use.

Use the green jumper for 24 volts.

Most 3 phase electric motors have a similar system for star or delta connection.

The current drain in the 24 volt mode won't be even but you could run the power
panel off one battery & the pump off the other.

Excuse the drawing (wife's laptop with crappy drawing program).

John.


Liam, the two 12 volt batteries will charge ok when wired in parallel from your existing charger
provided both are of similar age/condition, they will however take twice as long to charge.

Gray Beard

My Feedback: (-1)

Very few people bother to use a flight box to operate a starter these days. It's cheaper and easier to just go to Harbor Freight and buy a 24 volt drill battery and connect it directly to the starter. In my case I use an 18 volt on my starter and it is good for up to the DLE 30 and is fantastic for my 120 glow engines.
John Buckner got a lot of use doing it several years ago with the 18 volt and he has a couple starters set up on 24 volts. My field box is now nothing more then a tool and parts box. After my electric pump finally went dead I really have very little need for a flight box, a much smaller tool box could replace it any time.

Hircflyer

Except if you live in a place that has never heard of Harbor Freight and shipping cost are outrages

Gray Beard

My Feedback: (-1)

I'm sure HF isn't the only place that stocks electric tools and has the replacement batteries. If we had a member from India that could do it I would think anyone in the US could find a battery. Perhaps there may be a big chain hardware store on the island?? Maybe?

Redback

Sure, the motor will be trying to spin quicker, but you will have the internal resistance of the batteries in series, thereby limiting the current draw. Whereas with the batteries in parallel the internal resistance is halved.

Either way you only have the same amount of energy to work with.


Terry

liam_irish

Thanks John, I am in the process of adding the 2 new sets of female banana connectors to my field box. I just want to confirm that when I am using the green jumper for 24V, I will not short out my 12V power panel (the power panel will only be connected to one of the batteries). Is that right?

Thanks,

Liam

liam_irish

Posting again w/ quote this time -- I am in the process of adding the 2 new sets of female banana connectors to my field box (described in quote below and by diagram John provided). I just want to confirm that when I am using the green jumper for 24V, I will not short out my 12V power panel (the power panel will only be connected to one of the batteries). Is that right?

Thanks,

Liam

liam_irish

Well, I finally came to my senses and tested this configuration with my multimeter to make sure I wouldn't send more than 12V to my power panel. Works perfectly! Thanks for the advice guys!