A123 Battery Pack in the U-1

[chessmonster]

I have a bunch of a123 cells and if can i would love to run the cells in my new U-1.

Since the cells are 3.2 volts each, my best option would be to run 3 cells for 9.6 volt packs. I think this might be ok since from what i have read a123 cells put out less volatage out than the 3.2..something like 2.6.

My first question has anyone run higher voltage packs in the u-1 will this cause the esc controller to shut down. Will i have to replace the esc to run these a123 packs?

Will the extra weight of the 123 packs over lipo be too much for the boat?


Thanks for any advice anyone could give.

[Bill-SOCAL]

Well, the UL-1 is a 4S lipo boat, or 14.8 volts nominal. So you would need 4 A123 cells @ 3.3 volts per cell nominal and that would only get you 13.2 volts. Five cells would get you 16.5 volts.

But the issue then becomes capacity. The largest A123 are 2300 mAh cells. I am not sure if there is room for 10 A123 cells, which would get you to 4,600 mAh.

[chessmonster]

I think i could easily get 2 packs of 5 to fit pretty easily.

Does anyone know if this boat could handle that kind of weight?

A 10 cell pack would weight about a pound and a half.


I was thinking of running two 9.6 volt packs (3 cells per side 6 cells total) for a total of 19.2 volts...could i get a way with this?

[Bill-SOCAL]

I would not worry about the weight. A 4S 5,000 30C pack weighs about 19 ounces.

But you cannot put more than 4S lipos voltage to the ESC according to Aquacraft:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVSV4&P=ML

So you might want to give some thought to the A123 option.

[Flying Scotsman]

Bill is on the button

Douggie the stupid one

[sailr]

A123's haven't proven to be very good in "instant demand" situations. I also fly R/C aircraft. Experiments with larger brushless power systems have shown that if the throttle is advanced too quickly, 'demanding' instant current, the A123's won't do it... the ESC sees an undervoltage situation and shuts down. A close friend of mine in China is a chemical battery engineer that works for a company making the LiFe batteries (same as A123). He has confirmed to me that this is indeed a problem with the technology.

I was all hyped about them in the beginning and have a bunch of cells. Not sure what I'm gonna do with 'em. They're big, heavy, low capacity, and don't deliver. Beyond that I guess they're just fine.

[chessmonster]

Ok so created a pack 5 cells for a total of 16 volts. A big a123 pack. Its only a 2300mah pack and as expected its heavy. It is one big pack that i mounted with velcro in front of the motor. I was afraid it would sink the boat or upset its cg but it didnt :)

I also recieved a couple of regular lipo pack direct from hong kong at 3300 amp hours. 20 c packs. 7.4 volts.

Yesterday at the pond i tested both packs back to back. Running the lipos the boat was fast..probably close to the 45mph other people have been reporting out of the box. I kind of skimpled on the batteries..getting lower amp hour and only 20c..by the way i found these 2 packs on ebay 70 dollars for the both of them shipped straight from hong kong...

With the a123 the weight was not such a big issue because it actually made the boat more stable holding it down in the water..it seemed less likely to flip with the a123 pack..but the boat was considerably slower. This was kind of suprising since a123s are suppose to have a 30c discharge rate. I would say the boat was going at most 30mph with the a123.

I didnt have any cut offs yesterday with the a123 just disappoiting performance.

Of course the big plus with the a123 was i can charge the pack safely in 10 minutes using 10 amps. Also this pack is suppose to be good for 1000 charges so price per use is very low. But the poor performance just kills it.

A very knowledgable racer guy at the park who is a type who is at the different ponds racing and talking racing every weekend and has been doing so for years says he has never known anyone to run a123 packs in racing boats. That speaks volumes..if it was practical..then people would be running a123.

Regarding regular lipo...Do you guys think if i upgraded to a 5000mah pack i woiuld bet even a bigger boost in performance? If this is all about the amp hours then it would definately be worth it to spend the $ on a larger pack.

[Bill-SOCAL]

A very knowledgable racer guy at the park who is a type who is at the different ponds racing and talking racing every weekend and has been doing so for years says he has never known anyone to run a123 packs in racing boats. That speaks volumes..if it was practical..then people would be running a123.

I am not surprised by the results. BTW - where are you located in California and who was the fellow you are talking about here??

[chessmonster]

I am in San Francisco...

Oh...just realized he gave me a business card!

His name was Randy Naylor BBY Racing...he usually races in fremont he said and has well over 100 boats.

THanks for all the great information by the way Bill...you pretty much called it that the a123 cells wouldnt work...but i had the cells so i figured its worth a try...by the way..no way to fit 10 cells in that hull...

[sailr]

More AMPS pushes the voltage through faster and more efficiently. 5000mAh packs will give you a boost over 3600mAh packs.

The latest and best lipos will allow you to charge them at at least 2C (30 minutes) and some at up to 4C (15 minutes) BUT!!!! Keep an eye on 'em. I would NOT try this with the batteries from Hobby City, etc. You have to PAY for good batteries!

A123 (LiFePO4) batteries are not worth the expense, hassle, weight, etc.

[engineerjoe]

Well, i had the UL-1 out yesterday for the first time, man what a blast!!

I have a bunch of A123 packs from other RC's in different configurations. I'm not going to race and like A123's for the quick charge and durability. Here's what i found:

3000 NiMH 6 cell packs would get on plane but ran out of steam quickly

4s1p A123 (2300mah) would get on plane and were faster than the nimh but not by much. these cells fit in there great.

4s2p A123 (1100mah) same as above

Let me just say this, i got a great deal on this boat and figured I'd give 5s a shot on the stock ESC. If you payed retail for your boat (or don't want to take the chance of frying something) I would suggest getting a BEC and doing the red wire mod (this is what I did on my SV27)

5s2p A123 (1100mah cells) - this is where the boat came alive!! i would say it was hitting the upper 30's without any tuning, on the stock prop. With only 2200 mah of capacity run times were short, 4-5 mins. Everything stayed cool and the boat seems planted to the surface of the water.

[sailr]

Interesting results from the A123's. They work great in cars because the motors are geared way down. On an airplane, or boat, that demands quick response, the A123's "choke". Can't deliver the juice quickly. I have a good friend in China who is a battery design engineer. He has confirmed to me that this is a problem with the A123's.

Upper 30's is really slow for the UL-1. If you get a chance to try lipos, you will find it is an entirely different boat!

Well, i had the UL-1 out yesterday for the first time, man what a blast!!

I have a bunch of A123 packs from other RC's in different configurations. I'm not going to race and like A123's for the quick charge and durability. Here's what i found:

3000 NiMH 6 cell packs would get on plane but ran out of steam quickly

4s1p A123 (2300mah) would get on plane and were faster than the nimh but not by much. these cells fit in there great.

4s2p A123 (1100mah) same as above

Let me just say this, i got a great deal on this boat and figured I'd give 5s a shot on the stock ESC. If you payed retail for your boat (or don't want to take the chance of frying something) I would suggest getting a BEC and doing the red wire mod (this is what I did on my SV27)

5s2p A123 (1100mah cells) - this is where the boat came alive!! i would say it was hitting the upper 30's without any tuning, on the stock prop. With only 2200 mah of capacity run times were short, 4-5 mins. Everything stayed cool and the boat seems planted to the surface of the water.

[theShark]

I also have lots of A123 for planes, helis etc...I'm using 5S2P in the UL-1.