Electric IMAC Plane poll?

[rmarsden]

	Quote: Originally Posted by Judge
	My battery is a 54 amp-hour battery. So with a 200 amp-hour I might get 4 full charge cycles like the above. Your theoretical 13 charges ignores the voltage depression under load that the 12-volt battery will sustain. That will limit the actual number of charge cycles to something well less than the numerically calculated number which ignores the voltage depression.

You have run up against a battery property lnown as Peukert's law. It relates the effective capacity of a battery to its discharge rate. For a typical lead-acid batttery rated at 54A-Hrs, discharging the battery at 24 Amps actually reduces the battery's capacity to around 30A-Hrs (plus a minus a bit depending on battery design, quality, and prior usage). This is why you can only get one+ charge from your 54 A-Hr battery. By charging at a high rate from a samll battery, you reduced its capacity to only 56% of its labeled capacity. Note: lead acid battery capacities are usually specified for a discharge rate of C/20.

In contrast, if you were using a 200 A-Hr battery and discharging it at 24 Amps, the capacity only falls slightly to around 180 A-Hrs.

So, it is important to chose the right battery to charge the batteries you so carefully chose to power your boats and planes.

[Judge]

	Quote: Originally Posted by rmarsden
	So, it is important to chose the right battery to charge the batteries you so carefully chose to power your boats and planes.

Or just get a generator. Using a battery simply does not cut it when you need to do a lot of charging at high rates with lots of packs. I use a 2KW generator and a 90 amp power supply. Problem solved.

[Radioactive]

Bill, tell us more about your generator! price, etc.. thks don

[rmarsden]

	Quote: Originally Posted by Judge
	Or just get a generator. Using a battery simply does not cut it when you need to do a lot of charging at high rates with lots of packs. I use a 2KW generator and a 90 amp power supply. Problem solved.

Sure, one problem is solved - sourcing power. But now I need a vehicle large enought to transport the plane(s), generator, fuel for the generator, and power supply. And I need to be sure that no one will object to my generator noise and exhaust.

The 200 A-Hr battery is sufficient to get even your plane through a weekend IMAC contest, and the battery is smaller, lighter, and less expensive than your generator with power supply setup not including the additional cost to buy a bigger car, truck or add a trailer. I can fit my 35% plane, 200 A-Hr battery and all other necessary flying gear in my Ford Explorer. Somehow, I think your setup would be a bit too large for my Exploder.

Hope to see you at the April 4 EMAC at the SEFSD Mission Bay field!

[Judge]

Here is the generator: http://www.kipor.com/prouducts_detail.asp?info_id=87

About $800 on Amazon

Amazon.com: Kipor IG2000 2000 Watt Inverter...

://www.amazon.com/Kipor-IG2000-2000-Inverter-Generator/dp/B000RUOXYW/ref=pd_bbs_sr_7?ie=UTF8&s=home-garden&qid=1238599031&sr=8-7
They make a 1 Kw as well and it is less. It can be had for around $500 to $600.

Noise is rated at 54-59 dB so the folks at the field should not complain. Run a long extension cord and put it away from people and there will be even less notice given to it.

Yamaha and Honda also make similar products, but theirs go for nearly twice the price.

They are about the size of a 5-gallon gas can. No big deal. Just about anyone should be able to easily find plenty of room in the vehicle for it. It is not much larger than say a 200 amp-hour 12 volt battery and weighs much less.

For those still wanting to use a big battery the Odyssey brand are very good. This is their 126 Ah

http://www.odysseybatteries.com/battery/pc2250.htm

126 Ah = 86 pounds.

Or their 214 Ah battery: http://www.odysseybatteries.com/battery/pc1800.htm

214 Ah = 132 pounds.


1Kw generator = 31 pounds
2Kw generator = 48 pounds

75 amp P/S = 8 pounds

So 39 to 56 pounds versus 86 to 132 pounds.

And sorry Randy, I cannot make it to San Diego this weekend, but I will be at the Riverside pattern contest April 18 & 19, hope to see you there. Steve says he is coming!!

[rmarsden]

	Quote: Originally Posted by Judge
	And sorry Randy, I cannot make it to San Diego this weekend, but I will be at the Riverside pattern contest April 18 & 19, hope to see you there. Steve says he is coming!!

Great info on generators and batts.

Sorry to hear you won't make it for the EMAC. If I can finsh my Krill Spark in time for the pattern meet, I'll be there. But at my usual rate of construction, next year's meet is more likely

[Judge]

	Quote: Originally Posted by rmarsden
	But at my usual rate of construction, next year's meet is more likely

Ah, somebody who builds like I do!!!

[gareth.ky]

rmarsden, I like the idea of the battery solution. If I had a trailer that I could mount a couple in that's what I would do.

Judge is right about the comparative weight of a generator vs. batteries. Batteries are much heavier. I've seen the little Kipor in action and its not too loud but not quiet either. The energy density of batteries vs. gasoline means that is unlikely to change or a while.

Also if the 200Ah turns out not to be enough you kinda screwed. With the generator you can go get more gas. You can also use it to run other things in camp, like a hot dog cooker or a big fan.

Is the battery significantly cheaper than the generator?

[nate540]

I bought my 225ah batts for 79.00 each 4 years ago and they are still going strong. I guess it comes down to do you have the room and do you want to listen to a generator. They both have there pros and cons. like I said before I have two batts and a 300 watt inverter. Just last night we spent about 6 hours at the field charged several receivers a bunch 2700 3s packs and ran the inverter the whole time with florescent lighting, radios and other things. At the end of the night there was almost no drop in voltage on the batts. again you have to decide what is best for your app. all I can tell you is what I am doing but that may not work for you. Just my .02

[Royster]

I think a generator is not a bad thing as most of the complaints we get is from planes in the sky not on the ground!

Just as in camping sites here you can run an extension cord from the geny to your charger if you dont want to bother other campers, but at a club with screaming glow engines it wouldnt be a problem.

[rmarsden]

	Quote: Originally Posted by gareth.ky
	Also if the 200Ah turns out not to be enough you kinda screwed. With the generator you can go get more gas.

For a quick field recharge I just run jumper cables from the big battery to the car battery and run the car for 30 minutes. The big alternator charges the battery faster than most battery chargers and the car is very quiet compared to most generators.

Our field, SEFSD, in San Diego is inside Mission Bay Park so we fly only electric aircraft. A generator would be the loudest thing around except for the jet skis, ski boats, Harley's, etc. cruising on or around the bay.

[rmarsden]

Charger efficiency: just checked one of my Hyperion 1210i chargers for effciency.

Volts in: 13.25
Amps in: 8.65
Power in: 114.6Watts

Volts out: 19.81
Amps out: 5.00
Power out: 114.6Watts

Efficiency = 99/114.6 = 86%

This is not quite as good as I had hoped but not terrible. The newer chargers when run from 24V will likely be a bit more efficient.

[BoneDoc]

I fly 50cc conversions, and I drive my generator to the field . Not the most environmentally clean option, but I have no pretense that I fly "to save the planet" .

[Judge]

And again, people have to keep in mind what we are talking about here. If all you need t do is charge your receiver and transmitter pack and maybe some foamy packs, then a battery is fine.

But when you start talking about charging multiple big packs in a hurry, then a generator starts to make more sense. It also depends on the pack count in your plane (or whatever) 1P or 2P and the cell count. Running a 10S2P set up that you need to charge in under an hour requires 2 chargers each pulling around 25 amp at their peak. Even a big battery can only do that maybe twice. Sure, you can charge fewer packs and/or charge slower, but in a contest you may not have that luxury.

So again, it really depends on what you are charging, how many of them you have to charge, and how fast you need to charge.

[powerlines]

My Bud has the 3DHS 87'' SHP. It's BY far the best flying plane I have EVER flown..