Help w/ battery please...

[RCvolt]

Specs for a stock BJ motor and ESC ( see link below ) indicate that they will both handle 21 volts which is the rating for a fully charged 5 cell lipo (right?). I posted an inquiry (below) asking if the boat can handle the 2.8lb weight of 2 x 5 cell packs in parallel on the Blackjack forum but got no answer


https://forums.offshoreelectrics.com/...ead.php?t=8228

Motor:
http://www.proboatmodels.com/Product...ProdID=PRB3310

ESC:
http://www.horizonhobby.com/Products...ProdID=PRB3309

Reason I’m asking is… just like each and every person reading this, I’v gotten the bug. I now know that this hull is not the best and looking down the road, I’m hopeing I can use the lipo for something better.

This is my first boat that is not from ToysRus. I tried to learn as much as I can by reading as much as I can on different forums but I guess the question is............ just too bizarre to acknowledge????

If the question is throwing some people off balance, I assure you that I do not know enough to throw a line like this as a joke (i.e. “will this be to much weight? / can I throw a 55 gal barrel in the trunk for a gas tank?) I really don’t know! ( I can always put bigger tires, bigger motor, wider frame, etc, etc, short of sinking the car/er boat, right!?

PLEASE!!!!! I would really appreciate it if somebody can set me straight. I can handle the embarrassment better than spending big $$$ on the wrong stuff!

I know I’ll end up buying the big batt if I don’t get any advice

[Brushless55]

There are a couple threads on here where some have gotten away with 6s !
not that I recommend that..

[bwells]

5 cells gets you 18.5 volts, well under the stated 21 volts and paralleled is even better as it doubles the Mah, longer run time. Weight can be controlled by the placement of the batteries but be sure to see the posts on removing the stock trays and lowering them. Opps, weight can't be be controlled, I miss spoke! I like the 5 cell idea in parallel and I think you are on the right track and remember the fast guys throw in a gps and data logger that has to have some weight also

[Rumdog]

%s will work. disconnect the bec and run a receiver pack. dont worry about the excess weight, just find your cog and you'll be fine.

[Rumdog]

haha, i mean 5s

[bwells]

After thinking for a while, I run 2 8.,4 NiMH in series and it goes fast enough for me. The extra 2 volts can make a difference so stick the 3 pack to the back and the 2 pack in front but you are talking big bucks here but I'll bet it will scream. Let me know how it works so I can dream about what to buy when I hit the lotto!!!

[RCvolt]

Thanks for fast reply.

But my main concern is weight of the battery ...2.8 lbs on a blackjack 26.

Here are my excusses

1) Have a 2-3 year old matched pair of 2s 3700 polyrc in series that’s not all there anymore and want to move up.


2) First thought of doing a 2s and a 3s in series but again the weight distribution issue….one side will be substantially heavier. I thought about using the extra weight to counter the prop torque? But not too sexy??

3) I’m concerned about ability to adjust CG with batteries mounted parallel to transom between the motor.

4) Also, that leaves me with a 2cell and a 3 cell battery. I don’t know, but it just dosen’t feel right. Much better with a matched pair I think.

5) Tons of warning against 6 cells on this boat. The BJ26 is a good boat for the learning curve that will keep the midnight lamp burning…but I’d really like to keep an eye on my purchases with particular attention to a part or products application for future projects.
My next boat will not be a RTR.

I know one 5s battery will run the boat but will end up with serious weight distribution issue unless, if it will even fit ( that pack is a brick!), I mount the one 5s battery about 33% to the back of the boat parallel to the transom? I don’t think I want to do that. So Like you said, just get two 5 cells, parallel them, get long run time, and gentle on the battery. And when the time is right, I can series them on a nice exotic european cat …in my dreams
I’m not ready to start a new build, but I’d like to get ready.

Back to the subject….
Will a 26” blackjack handle a 2.8 lb battery? don’t really want to end up with a retriever / tug boat or espresso machine on the lake after going crazy on upgrades.
1 step forward, 2 steps back…get a bigger boat for the new batt? omg. I have 2 young kids. Help me out…2.8 lbs of battery on a 26” boat, will it work?

[Brushless55]

Are you saying one battery is 2.8lbs or the total of two?
That is alot of extra weight..
My total weight for 2 2s batteries is just over 1lb

[cyberhoops]

In my opinion I don't think the weight will be a problem. I have seen 26 inch hydros that have a total weight from just over 4lbs to nearly 6.5lbs and all of them run just fine.

[RCvolt]

After thinking for a while, I run 2 8.,4 NiMH in series and it goes fast enough for me. The extra 2 volts can make a difference so stick the 3 pack to the back and the 2 pack in front but you are talking big bucks here but I'll bet it will scream. Let me know how it works so I can dream about what to buy when I hit the lotto!!!

I checked the dimension of the battery. They will not fit parallel to the transom.
As for the cost, really not to bad – see link below

http://www.hobbycity.com/hobbycity/s...idProduct=7654

[RCvolt]

In my opinion I don't think the weight will be a problem. I have seen 26 inch hydros that have a total weight from just over 4lbs to nearly 6.5lbs and all of them run just fine.

I seem to remember Fluid mention something about adding a little weight ot the boat to actually improve performance. Am aware that it will vary depending on hull and setup, just didn’t know how much is too much for this boat…. Better to use battery as ballast instead of lead right?

[RCvolt]

Are you saying one battery is 2.8lbs or the total of two?
That is alot of extra weight..
My total weight for 2 2s batteries is just over 1lb

Weight of each battery is 1.4 lbs each x 2 = 2.8lbs total

[RCvolt]

I made a mock up of the battery using specs / dimension posted. I might have to relocate the water outlet for the cooling system. It will be tight but doable. But like I said the battery is like a brick and will be sitting up high bringing center of gravity up with it. Now worried about roll over issues which is why battery tray is removed, right?
I know, I know….want to have the cake and eat it too.

Man…this hobby get’s expensive really fast and it’s never enough!!

[RCvolt]

p.s.

can somebody tell me how to do a multiple post?