Author Topic: Charging at the field (Read 4203 times)

James Mills · « **on:** June 19, 2013, 03:10:49 PM »

I have seen some flyers use a car battery to run their charger at the field and was wondering how to decide what battery to use? I have an I-Charger 306b and our local flying site has no electric hookups and I'd like to be able to charge at the field as we fly.

Thanks,

James

Tim Wescott · « **Reply #1 on:** June 19, 2013, 04:11:39 PM »

Something rated for deep discharge -- real car batteries are designed to give lots of current for starting, but never sucked dry. Deep discharge RV batteries are the opposite -- they're not happy delivering hundreds of amps for a few seconds to start a car, but they're much more tolerant of being mostly discharged over and over again.

Crist Rigotti · « **Reply #2 on:** June 19, 2013, 04:12:13 PM »

Use a marine or a deep discharge battery. They are made to be discharged to a lower voltage. I usually just use my car battery if I have to charge the batteries 4 or 5 times. I can always start the car after about 6 batteries and let the car battery charge while charging the lipo's. Don't start the car with the charger connected. It doesn't need the drain and surge of starting a car.

John Hammonds · « **Reply #3 on:** June 19, 2013, 04:27:01 PM »

I'll echo the replies above, A leisure battery is the way to go. I broke all my own rules and I use a battery which came off a BMW 7 series and am still using it after 3 years with no apparent issues but generally speaking you need a battery designed for relatively low current but for a long time. (Automotive batteries are designed to deliver a lot of "Cranking Amps" for a few seconds).. Having said that a trip around a few automotive shops will get you a battery which has failed the "Drop Test" (A lot of amps for a short period) and can be picked up for next to nothing. The secret with these is to keep them fully charged (As they would be if located in there normal environment). As I said the type of battery designed for marine use or in a leisure vehicle (Caravan, motor home etc) is what you really need but if an automotive battery is available at the right price don't pass it up.

TTFN
John.

Larry Wong · « **Reply #4 on:** June 19, 2013, 07:33:26 PM »

At are field we have power supplied by the city, I can charge 4 at the same time , one power supply and 2 cell pro 10's charger's with balancer, and all this is on the city's nickel ...

James Mills · « **Reply #5 on:** June 19, 2013, 08:30:45 PM »

Quote from: Larry Wong on June 19, 2013, 07:33:26 PM

At are field we have power supplied by the city, I can charge 4 at the same time , one power supply and 2 cell pro 10's charger's with balancer, and all this is on the city's nickel ...

Okay Larry rub it in

James

Howard Rush · « **Reply #6 on:** June 20, 2013, 12:01:29 AM »

Costco had two sizes of deep-cycle batteries when I got mine. I got the smaller one. It may be inadequate. The second pair of flight batteries I charge with it (14 amps to the flight batteries when they're both in CC charge mode) causes the charger to hit its 10V cutoff.

Igor Burger · « **Reply #7 on:** June 20, 2013, 12:30:48 AM »

LiFePo4 is the key word :- )))

Howard Rush · « **Reply #8 on:** June 21, 2013, 02:05:32 PM »

Quote from: Igor Burger on June 20, 2013, 12:30:48 AM

LiFePo4 is the key word :- )))

Allow me to translate from the Slovak: that's $$$.

Igor Burger · « **Reply #9 on:** June 21, 2013, 02:14:17 PM »

yes it is about $$$ but it lasts several times longer and gives 100% paper capacity and weights only fraction of lead acit battery ... if you count it all together it comes cheaper

I can do safely 8 flights from battery which I have in the field box, sometheomes even 9 or 10

I use my battery 4 years withou any sign of lower capacity or power (resistance)

Igor Burger · « **Reply #10 on:** June 21, 2013, 02:35:27 PM »

http://pavelrichter.net/wp-content/uploads/2012/04/12v-40ah-pack.jpg

Howard Rush · « **Reply #11 on:** June 21, 2013, 03:34:25 PM »

Quote from: Igor Burger on June 21, 2013, 02:14:17 PM

if you count it all together it comes cheaper.

Yes, if I include the cost of physical therapy for my back because of lifting the lead-acid battery.

Rudy Taube · « **Reply #12 on:** June 23, 2013, 11:26:02 PM »

Igor has the very best (cost is no object) solution, by far. For around $160, +/- $30, you can get a 12V battery that weighs around 7 pounds and will charge all your batteries at the field. These are very easy to carry and charge, and will give you around 2,000 cycles at full power.

http://www.amazon.com/Bioenno-Power-E-Scooters-Wheelchairs-Appliances/dp/B009XMPTUM/ref=sr_1_44?s=electronics&ie=UTF8&qid=1372049831&sr=1-44&keywords=lifepo4+battery

This solves the problem Howard brought up: Big Car, or RV, or Marine batteries will *&

(mess?) up your back. Like Howard mentioned, when you factor in the Dr. bills for the back surgery the price of these batteries is more than reasonable.

Less expensive, compromise solution:

These are what I used before I started taking 5 ECL and 5 ERC batteries to the field. I bought 2 of these batteries and they give 3 full charges each (4 if you fly gently ;-). If you have three ECL batteries and just ONE of these 12V batteries you could get in 6 flights, which is enough for most people. 2 of them would be enough for even the most ardent competitor. They each weigh only 17 pounds. They have carry handles molded into the top of the battery that makes them very easy to carry at your side. NO back issues Howard, I promise! :-) These are sealed batteries, no leakage, store in any position, etc.

http://www.amazon.com/HR22-12-Genuine-BB-Battery-hour/dp/B002UAPDBO/ref=sr_1_7?s=electronics&ie=UTF8&qid=1372047440&sr=1-7&keywords=wheelchair+battery

Nuclear reactor solution ..... BEST :-)

Using the nuclear reactor that mother nature gave us is by far the best long term solution to charging our batteries at the field. This is what we use at one of the LA CL club sites. I'm lucky to fly at a park one block from my home here in LV, but if I had to fly far from home I would use one of these:..... Here is a link to one for your personal use. There are many options to plug into the free reactor, this is just one that seems to fit our small ECL needs. ..... Howard, Please let this forum know how these work out when you get one. :-)

http://www.amazon.com/Solar-Link-Power-Center-Collector/dp/B00B5Y1KCW/ref=sr_1_125?s=electronics&ie=UTF8&qid=1372049615&sr=1-125&keywords=lifepo4+battery

Robert-Jan · « **Reply #13 on:** June 24, 2013, 01:21:05 AM »

Quote from: Rudy Taube on June 23, 2013, 11:26:02 PM

Igor has the very best (cost is no object) solution, by far. For around $160, +/- $30, you can get a 12V battery that weighs around 7 pounds and will charge all your batteries at the field. These are very easy to carry and charge, and will give you around 2,000 cycles at full power.

http://www.amazon.com/Bioenno-Power-E-Scooters-Wheelchairs-Appliances/dp/B009XMPTUM/ref=sr_1_44?s=electronics&ie=UTF8&qid=1372049831&sr=1-44&keywords=lifepo4+battery

Be aware it is "only" 15Ah.
Depending on what battery you are using it is only enough for about 3 charges.

Greetings Robert-Jan

John Rist · « **Reply #14 on:** June 24, 2013, 10:29:50 PM »

Anybody consider a small generator? Here is one that weighs less than 25 lb. Puts out 450 W (about 4 amps at 115VAC). Cost $400.
It has the advantage of being quit.

http://www.northerntool.com/shop/tools/product_200487786_200487786

If you can stand the noise: I have one of these and at $350 I can use it as backup power for my home. It puts out 30 A @ 115Vac. It runs the air conditioner in my Coleman camper. The camper has a 12 Vdc power supply that is active when the generator is running for running chargers.
It is louder than the Honda style generators but it makes less noise then most fuel power stunt ships. O yes it is heavy @ 100 lb. Wheel kit recommended.

http://www.campingworld.com/shopping/item/champion-4000-watt-portable-generator-49-state-model/67293

Robert-Jan · « **Reply #15 on:** June 25, 2013, 07:05:32 AM »

O use a Fuel cell.
The funny thing is they work on ..... methanol!!!.

Greetings Robert-Jan

Howard Rush · « **Reply #16 on:** June 29, 2013, 03:08:34 PM »

I may have mentioned that the wife of the guy who builds my airplanes funds my modeling activities. I asked her today for funding for a small generator, pointing out that sometimes power to the house goes off in the winter, and it gets chilly. Funding was denied.

Howard Rush · « **Reply #17 on:** June 29, 2013, 03:26:48 PM »

So back to using a battery to charge flight batteries at the field. I took some measurements to see if my Costco battery is defective or just too small, hence whether I should return it and invoke my sliding-price warranty. My charger takes 29 amps from the 12V server power supply to put 14 amps into my flight batteries (two 5S batteries both on the constant-current charging phase at 7 amps each). An interesting phenomenon is that the lower the battery voltage goes, the more current the charger takes to deliver 14 amps to the flight batteries (an instability allegedly also seen on airliners and space stations). Charger input current from the Costco battery got up to 32 amps while I was watching, and the voltage to the charger eventually got to the 10V cutoff. This was on the first pair of flight batteries I charged after filling up the Costco battery. I have a fuse in the circuit, the current-measuring shunt, and an extension cord so I can leave the battery in the car while getting the charger far enough away from the car that I can still get home if a battery blows. All this claptrap was causing a 2V drop from battery to charger. I think the lesson is that hooking the charger directly to the 12V battery, although inelegant, is probably the way to go.

jfv · « **Reply #18 on:** June 29, 2013, 07:24:05 PM »

I use a charging station I put together powered by two Dell 6650 server power supplies wired in series. Max output is 72A @ 24V. 120V power is supplied by a generator. There are three power taps, one 24V and two 12V. It works great for outings as multiple chargers can be connected via a double sided buss bar that's connected to the two 12V taps.

Howard Rush · « **Reply #19 on:** June 30, 2013, 12:05:57 AM »

Very cool. I like the idea of a generator. There must be a way to wire a Prius to do that.

Larry Renger · « **Reply #20 on:** July 02, 2013, 04:09:46 PM »

How about a Tesla? Bet you'll never run that battery down.

Tim Wescott · « **Reply #21 on:** July 02, 2013, 04:55:01 PM »

Quote from: Howard Rush on June 29, 2013, 03:26:48 PM

So back to using a battery to charge flight batteries at the field. I took some measurements to see if my Costco battery is defective or just too small, hence whether I should return it and invoke my sliding-price warranty. My charger takes 29 amps from the 12V server power supply to put 14 amps into my flight batteries (two 5S batteries both on the constant-current charging phase at 7 amps each). An interesting phenomenon is that the lower the battery voltage goes, the more current the charger takes to deliver 14 amps to the flight batteries (an instability allegedly also seen on airliners and space stations). Charger input current from the Costco battery got up to 32 amps while I was watching, and the voltage to the charger eventually got to the 10V cutoff. This was on the first pair of flight batteries I charged after filling up the Costco battery. I have a fuse in the circuit, the current-measuring shunt, and an extension cord so I can leave the battery in the car while getting the charger far enough away from the car that I can still get home if a battery blows. All this claptrap was causing a 2V drop from battery to charger. I think the lesson is that hooking the charger directly to the 12V battery, although inelegant, is probably the way to go.

Suggestions:

Try lowering the constant-current setting in the charger
Keep the extension cord, but use way bigger wire. 30 amps is lots. If you have an ARRL handbook lying around it'll tell you ohms/1000 feet for various gauges of wire. If not, post how long you want the cord to be and what drop you'll stand, and I'll post you a suggested gauge
Just based on thermodynamic considerations, the current draw on the 12V side should drop if the battery voltage goes down. If not, something in that there charger is getting hot
- That's just wrong. Didn't those people do any TESTING? (Your charger people -- new airliners are just expected to crash or burn up or something)

Dean Pappas · « **Reply #22 on:** July 02, 2013, 07:38:31 PM »

Hi Gang,
I don't understand the problem ...

... I've charged 10S 5000 mAh batteries from my minivan battery quite often.
Yes, that battery requires a 15 or 20 minute idle after each charge, but a 5S 2700 should require maybe 3 charges before the car needs to be idled again.
Yes, beefy cables like Tim suggests are necessary.

Regards,
Dean P.

Tim Wescott · « **Reply #23 on:** July 02, 2013, 07:45:13 PM »

Quote from: Dean Pappas on July 02, 2013, 07:38:31 PM

I've charged 10S 5000 mAh batteries from my minivan battery quite often.
Yes, that battery requires a 15 or 20 minute idle after each charge

I think the published numbers for car batteries just don't match what we're seeing. If those batteries are 75% depleted, you should take about 12A-h out of your minivan battery, and that's the number I got for a battery to fit my car. Granted, my car is pretty small, but if you believe the numbers, that charge cycle should still be taking a bigger whack out of the battery than is healthy for it.

So either you have a new car battery sooner in your future than you expect, or once again the old engineer's maxim is true: in a fight between palpable reality and numbers from theory, reality wins, every time.

Howard Rush · « **Reply #24 on:** July 03, 2013, 12:58:30 AM »

Quote from: Tim Wescott on July 02, 2013, 04:55:01 PM

Suggestions:

Try lowering the constant-current setting in the charger
Keep the extension cord, but use way bigger wire. 30 amps is lots. If you have an ARRL handbook lying around it'll tell you ohms/1000 feet for various gauges of wire. If not, post how long you want the cord to be and what drop you'll stand, and I'll post you a suggested gauge
Just based on thermodynamic considerations, the current draw on the 12V side should drop if the battery voltage goes down. If not, something in that there charger is getting hot
That's just wrong. Didn't those people do any TESTING? (Your charger people -- new airliners are just expected to crash or burn up or something)

My interim fix is just to stagger the charging so that only one battery is in constant current mode at a time. I have to visit the charger every flight instead of every other flight. By and by I'll do some measuring to find how much the voltage drops in each piece of claptrap.

The charger is a regulator. If it puts out a given power, it will draw more current as the source voltage peters out.

I have no first-hand knowledge of this alleged DC bus instability; it's speculation by a geezer with whom I used to work. Nor do I know what the 787 problem was. One can't tell from the fix, either.

Pop the hood on your car, please, at the next contest so I can charge from your battery. Thanks.

Tim Wescott · « **Reply #25 on:** July 03, 2013, 08:44:28 AM »

Quote from: Howard Rush on July 03, 2013, 12:58:30 AM

The charger is a regulator. If it puts out a given power, it will draw more current as the source voltage peters out.

I misread your original post -- whoops. I thought by "battery" you meant "battery under charge". There are too many batteries running around for me to keep track. Yes, if the source voltage drops then the current pulled from it will increase. Switchers just work that way.

Quote from: Howard Rush on July 03, 2013, 12:58:30 AM

I have no first-hand knowledge of this alleged DC bus instability; it's speculation by a geezer with whom I used to work. Nor do I know what the 787 problem was. One can't tell from the fix, either.

The DC bus instability is a known issue with switching supplies of any kind. The only way that you can pull a constant power from a varying source is to present a negative resistance to the source. When the source's effective resistance exceeds your negative resistance, the bus is unstable.

I recognize the description of the fix on the Dreamliner. I've had to do that sort of thing myself. They shot-gunned it, and then they instrumented the hell out of it in hopes that when the real problem happens again they'll come home with enough data to implement the real fix. They pretty much said as much.

Dean Pappas · « **Reply #26 on:** July 03, 2013, 10:41:58 AM »

Quote from: Tim Wescott on July 02, 2013, 07:45:13 PM

I think the published numbers for car batteries just don't match what we're seeing. If those batteries are 75% depleted, you should take about 12A-h out of your minivan battery, and that's the number I got for a battery to fit my car. Granted, my car is pretty small, but if you believe the numbers, that charge cycle should still be taking a bigger whack out of the battery than is healthy for it.

So either you have a new car battery sooner in your future than you expect, or once again the old engineer's maxim is true: in a fight between palpable reality and numbers from theory, reality wins, every time.

My minivan has a 40 A-H battery ... actually 38 according to the label.

Tim Wescott · « **Reply #27 on:** July 03, 2013, 10:44:30 AM »

Quote from: Dean Pappas on July 03, 2013, 10:41:58 AM

My minivan has a 40 A-H battery ... actually 38 according to the label.

There you go! I guess if I switch to 'lectric I'll be getting a bigger battery for my car, or a bigger car for its battery.

Howard Rush · « **Reply #28 on:** July 03, 2013, 11:27:18 AM »

Quote from: Tim Wescott on July 03, 2013, 08:44:28 AM

I misread your original post -- whoops. I thought by "battery" you meant "battery under charge".

I figured as much.