Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[RickTheBlue]

I want to put 2 11.1v batteries into my speedboat and assume I need to wire them via some kind of  Y connection. Do I buy one, if so from where or can I make my own.


I know this seems a question that's been asked a million times but Im new and not very bright so help please


Rick

[TomHugill]

Are you wanting to join in series of parallel? Ie longer run time or more voltage. Wha connectors are you using? Lots of y harnesses available, use google!

[RickTheBlue]

Hi Tom
Thanks for the reply, I think the connectors are the large white rc car type but as the batteries are in the post I'm not 100% yet. I think I want run time over power at the moment but that might change once I try it out if the speed isn't enough. I understand that there might be a way to fit a switch that would allow me both but I don't really understand the ins and outs.


I've tried a google search but don't seem to get the right response, can you suggest a search term that would work?


Regards
Rick

[TomHugill]

http://eBay.co.uk/itm/400677350563

Does this help? They sound like tamiya connectors so googled tamiya y harness parallel 

[boatmadman]

Be careful if you think about using a switching arrangement, depending on battery capacity and stall current of the motor(s) there is the potential to draw significantly high currents through the circuit.


If you know the max burst current the batteries can supply, you will need a switch in excess of that capacity so as to allow a safety margin.


Also, you need to think about the load capacity of connectors, if they are underrated its not unusual to have the solder melt in the connector with subsequent loss of power.


Ian

[RickTheBlue]

Thanks very much Tom and Ian.


I've ordered a y connector from eBay and will see how that works out first. I have managed to obtain two sets of batteries both sets with a discharge of 30 to 40 c. One pair are 7.4 2200 mah and the other pair 11.1 4000mah so wil do a bit of trial and error I think until I find the best set up.


I don't expect to get much running time from either set given the performance I expect from the motor but can afford mega expensive batteries


Thanks for your insight, I appreciate it


Rick

[Netleyned]

How do you go about balancing two lipo packs in series or parallel.
I understand that each pack has its balance plug to balance the cells
in each pack, but how do you balance one pack to the other?


Ned

[Subculture]

I wouldn't run lipos like that. One pack will discharge quicker than the other,a nd the then the other pack will start to charge it, with no current limiting. Really good way to start a fire you can't put out until the boat is burned to a cinder.

If you want more capcity, buy a bigger pack.

[TomHugill]

Be careful of how much current your pulling through those tamiya connectors. I melted the ones in my Najade running it on 14.4v. If your looking for more performance I would look at other connectors (deans, xt60, 4.0mm bullets etc). Regarding batteries you can get get lipos off hobbyking uk very cheaply.

[TomHugill]

I agree with sub, I always run matching packs when going in parallel 

[RickTheBlue]

Thanks lads.... Back to the drawing board!!!

[Bill D203]

Action do a parallel battery set up. I use two 11.1volt 5000mah lipo batteries on one of these and it works OK but it is only driving a 900 brushed motor , not megger amps.
Never use Tamiya connectors they overheat and burn up. I use Deans type connectors which work fine But i repeat  not big current load.

[Bill D203]

Here is the link.
http://www.action-electronics.co.uk/pdfs/P103.pdf

[boatmadman]

Even with those relatively low capacity batteries, you have the potential for large circulating currents.


For example, the 4000mah batteries with 40c rate have a burst current max of 160 amps. So, you need the rest of the circuit components to at least equal this current carrying capacity. That means an esc of at least 175a, allowing for a safety margin. Connectors...4mm bullet connectors have a max load capacity of 150a, so 6mm is prob the best bet.


I have a bit of experience with these esc  things burning out, single phasing, connectors melting, batteries bursting into flames etc and its expensive if you dont get it right.


One VERY important thing to get right is getting the connections soldered onto the cable properly. I thought I had it sorted but was going through esc's at an alarming rate until I discovered that my connector soldering wasnt as good as it should have been, causing arcing in the connector, overheating, melting, battery swelling and esc failure due to single phasing.


Get it all right and they are a great power set up, get it wrong and it costs money, and if you are really unlucky, may get you a burnt out boat!


I recommend you read up on the safety instructions on Lipo batteries, along with charging advice.


Here is an interesting video:


http://www.youtube.com/watch?v=5J96ywv7yAM


Not trying to put you off, just want to make sure you are aware of the risks these things carry with them.


Ian

[Subculture]

4000mah batteries with 40c rate have a burst current max of 160 amps. So, you need the rest of the circuit components to at least equal this current carrying capacity. That means an esc of at least 175a, allowing for a safety margin.

Don't agree with that. You should fit a fuse to guard against short circuits. ESC rating should be based on the maximum current draw of the motors you have hooked up to them, plus a safety margin of about 50-100%, e.g. if you have a 10A draw I would go for at least a 15A or 20A (continuous) controller to ensure long term reliability.

Most ESC's can handle considerably more than that for very short periods e.g. the time it takes for a fuse to blow.

[malcolmfrary]

Don't agree with that. You should fit a fuse to guard against short circuits. ESC rating should be based on the maximum current draw of the motors you have hooked up to them, plus a safety margin of about 50-100%, e.g. if you have a 10A draw I would go for at least a 15A or 20A (continuous) controller to ensure long term reliability.

Most ESC's can handle considerably more than that for very short periods e.g. the time it takes for a fuse to blow.

+1  Its the motor and whatever is loading it that determines current draw, not what the battery is theoretically capable of delivering.  So the ESC is determined by the load it is to drive, and the fuse protecting the battery from a faulty ESC needs to be between expected max draw and what the ESC is capable of handling.  The wiring needs to be man enough to survive whatever blew the fuse, should that ever happen.

[nick_75au]

Ok I tried hooking a fully charged Lipo and a flat one together in parallel a while ago to prove a point, they were 3 cell 5000 mah packs. I had absolutely no spark, hot wires or anything. Even 200 AH lead acid connecting flat ones to charged ones has very little of anything happening.


 I would not hook a set of packs together in series with different charge levels and then draw current but charging with balancing is OK.


To series charge Lipos needs a special balance plug or board, my charger came with one, it is critical to get the balance plugs right or you will burn the board.


Parallel charging is preferred, there are boards available from HobbyKing and others to make it easy.


Lipos can come as paralleled packs they will have a 2P designation, no board or diodes or anything. Not as common these days with the availability of larger capacity packs.


Dont connect different capacities together, connecting 2 voltages IN SERIES is ok as well for discharge IE a 4 cell (4S) and 3 cell (3S) to make a 7 cell (7S)for example. ONLY 2 batteries of the same capacity and voltage can be connected in parallel.