Converting 12VDC-24VDC

[Resasi]

I had bought a 12V battery that was an ideal size for where I wanted to put it in order to use it with a 12V prerotator. It appears now that due to some unsorted issues we will actually now going with a 24V prerotator.

I was going to try to sell our new high performance Odessy and buy two smaller cheaper 12V batteries, but a thought did occur. I am aware that one can convert 12VDC to 24VDC. Are there any small compact converters that are not too heavy that might do the job.

I am in the process of finding out just what the motor needs.

[Caribean_gyro]

I use 2 from ameriking coverter for my 28 volt retarctable landing light. they are power hungry and a bit expensive. you have to check amp loading. becasue you might need to have 2 in parallel

chuckP

[Caribean_gyro]

http://www.aircraftspruce.com/menus/av/convert.html

a link

[brett s]

Something that can handle the current draw of a prerotator would likely be heavy & expensive.

[lanichol]

You defeating your own purpose. volt x amps = watts. Double the volts you need half the amps, but if you start with 12 volts and convert to 24 you get half the amps and you have not changed anything. I have seen a single odessey batteries replace two batteries in a diesel pickup. The odesseys are great, but you can not use a trickle charger or it wil ruin the battery.

[Resasi]

Thanks for that Chuck.

Larry I was just on that very subject on a second thread. Robert had told me about being careful about charging them. Does that mean I have to get a special and presumably expensive charger especially for this type?

OK sounds as though my idea isn't feasible then. Pity because I am now going to have to find two smaller 12V ones and find somewhere safe/good to put them.

It fitted really neatly, was safe, and close to the thrustline, which at 13lbs was good.

I suppose a + might be that I can now use the two to try and fine tune the CG position.

Bret, I was trying to find out what the draw is, and yes the weight and cost had occurred to me.

[lanichol]

Thanks for that Chuck.

Larry I was just on that very subject on a second thread. Robert had told me about being careful about charging them. Does that mean I have to get a special and presumably expensive charger especially for this type?


No any charger, just not trickle. We have a local landowner that is actually an odessey rep. in Texas that sell batteries to the farmers. The smaller batteries have a pretty good punch as the farmers run lots of things with their 4-wheelers; sprayers, seeders, winches. Two 4-wheeler batteries do not take much space.

[Aviomania]

Leigh,
The prerotator draws 100A. a 12v to 24V step up of 3-10A is easy and cheap to make.......but 100A!!!! it will cost a 4 digit amount!!! plus extra weigh, plus losses, plus heat, pluss...........

the 2 small 12V batteries i am suggesting cost $40 both, weigh 10 lbs both (lighter than the Odyssey) and if mounted next to each other measure 6" long x 5" wide x 4" high OR 12" long x 2.5" wide x 4" high, depending how you want to install them.

[Resasi]

Thanks Nicolas, had emailed you but you saw this first. OK that is the final word on it. And if you give me the required specs for the two replacement batteries I will start looking.

Brand new unused Odessy is now looking for a new home. Taken out of box and put on the gyro where it was sitting waiting for the pre-rotator.

Just talked to Stuart, the box and papers got dumped in the garage clear-out to store stuff for the Parents-in-law move and we took the gyro to Zephyrhills.

Will ship to anywhere in US. I will look for the credit card receipt then give a reduced price on that. Shame it looked like a really good battery

[vickijohnk]

Resasi, I once had a battery system for starting a jet engine race car that had two large 12V batt. They operated in parallel normally and charged from the truck electrical system, and in series (24V) to start the engine. I think I did it with two heavy duty relays.

John K.

[lanichol]

Interesting, not sure how you switch the relays with the engine running. What if one of the relays sticks?

[vickijohnk]

lanichol, I think the setup had one normal battery that ran the truck and the two jet start batteries. When the start switch was on, the jet start batteries were isolated from the truck, switched to series (24V), and power was directed out the power cable. When the start sw was off, they went back to parallel. There was also a "control power switch" to isolate the jet start system while starting the truck. We though the extra power (12V) from all three batteries might damage the starter motor.

John K.

[Resasi]

Now looking for smaller, powerful 12V Batteries that are not as costly as the Odessy. Found these Scorpions.

Anybody had any experience with them?

http://www.batterystuff.com/batteries/motorcycle/sYT5L-BS.html
Dimensions: 4 1/2" L x 2 13/16" W x 4 1/4" H
Polarity: [- +]
Actual Weight (lb.): 4
Shipping Weight (lb.): 5
DC Output Voltage: 12 V
Amp/Hr: 4
C.C.A.: 110
OEM Ref: YTX5L-BS, YT5L-BS
Manufacturer: Scorpion

[C. Beaty]

4 AH means the battery will supply 4 A for 1 hour or 1 A for 4 hours.

At 100 A, duration = 4/100 = 0.04 hours or 144 seconds.

Unfortunately, as current draw increases, AH capacity decreases due to internal losses in the battery (burned up as battery heating).

Also unfortunately, C.C.A. (cold cranking amps) rating allows battery voltage to sag to, I think, 8 volts. Google it to find out the exact number.

It is my guess that you need huskier batteries.

[Aviomania]

Leigh,
they are heavy for there capacity.
There are a lot of brands that makes 12V 8AH sealed lead acid batteries and they weight 4.8 lbs.

The motor draws max current only for about 15- 20 seconds (From 60-120) RRPM the rest of the time the PWM controller and the airspeed accelerating the blades drops the Amps down. average Amp draw from start to take off is around 50 Amps

here is a lick for the battery. this a 7.5 Ah... you can find 8 Ah. We have been using this batteries for more than 160 hours and have no problem.

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2147

[Resasi]

Thanks Nicolas, those look good as well. I assume from your comment re weight for capacity that the one's you are recommending have a better weight to capacity ratio? Or good enough for the job at a better cost possibly.

If you have been using them with no problems that would seem a sound enough recommendation. The price is certainly better.

I guess the 100A draw was variable and falling then Chuck, which allows for the smaller capacity. My electrical knowledge is very basic.

[vickijohnk]

Resasi, Do you intend to use the system "Total Loss" or are you going to charge the batt while flying? Does your engine driven generating system need the battery in the system to operate correctly? What is your target weight for the batt system? (LBS please). Could you run the gyro with a 24V system?

John K.

[Resasi]

John you are speaking to a neophyte wet behind the ears. As I know it the engine driven generating system does not need a battery in the system and will provide power for it's own ignitions. It will charge a 12V battery if one is in the system

I am hoping to be able to charge both these 12V batteries in flight.

[Aviomania]

Leigh.

The system will work like a normal 12V system and the batteries will be charging and have a constant 12V supply to the instruments. It will give 24V ONLY to the prerotator when operated without stopping the 12V supply to the instruments.