Batteries

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Viewing 8 posts - 1 through 8 (of 8 total)

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15 July 2008 at 15:08 #14694
Dan Walker
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@danwalker
Hi Guys,

Many of you may have read my previous posts and noticed i am building a Speedline 1:12th Trent Lifeboat Kit. I have finally got the prop shafts in etc and am ready to now start fitting out the motors and electronics. I have purchased the following…
- 2 x MFA Torpedo 850’s
- 2 x Electronize FR30HX ESC’s (30 amp)
- 2 x 30 Amp Inline Fuses
- 2 x 12v 7.0 Ah Lead Acid Batteries
I have bought 2 x 12v 7.0 Ah lead acid batteries thinking i would benefit from excellent playing time, using one for each motor and speed controller. I have based this on other builds of the severn speedline kit, one by phil locke and the other by terry small. The only difference is that they use 4 motors in total for the severn as appose to 2 for my trent. Am i best only using one battery or two? I also plan to have a water pump system for each exhaust regulated by the ESC and also a sound unit or two again being run off the 12v batteries. Space isnt that much of an issue as i effectively have a football pitch to put all my electronics into, balance and how she sits in the water is an issue though.

What do you think?

Dan
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15 July 2008 at 16:52 #14701
60watt
Participant
@60watt
Hello Dan,

I think the 30 amp rated fuses will not prevent catastrophic damage in the event of a fault.If you do your homework on fuses you may find they require a considerably long time to blow at even twice the normal rated current.

I would also avoid a fuseholder with a low temperature thermoplastic housing.I have seen cases where they melt and cause an open circuit at normal

For protection I would use a 12/16 volt polyswitch with a current rating just above the normal full-throttle motor current, to ensure stall protection.

tom edison
20 July 2008 at 23:43 #14761
JC Uknz 1
Participant
@jcuknz1
I use these 7.2Ah 12v batteries [the heavy brutes ] and find that they run all day [ even though mine are ‘junked’ ones from another purpose] ….the boat I’m thinking of is powered by a single 24v motor so consumption well down on your project. I would have thought it better to arrange the batteries in parrallel rather than one for each motor. The greater capacity will give you a ‘working power’ longer as they eventually run down.
21 July 2008 at 17:29 #14777
60watt
Participant
@60watt
Quote… "I would have thought it better to arrange the batteries in parrallel rather than one for each motor. The greater capacity will give you a ‘working power’ longer as they eventually run down."

Electronize speed controller instructions say in a paragraph titled "WIRING" that you should not do this on account of the "common negative ground connection between receiver circuit and speed controller".

Apart from the interference problem,a bad negative connection results in upwards of ten amps through the connections to the receiver……ouch.
21 July 2008 at 21:00 #14789
JC Uknz 1
Participant
@jcuknz1
Yes but I don’t use these gadgets and normally control speed with the tried and true ‘Bob’s board’ type of controller so such problems do not occur. I did buy a built-up Electronize but not particularly happy with it compared to my home made BB style controllers .. one problem are fuses continually blowing, a problem I do not have with BB’s which are not fitted with fuses.

My BB’s are simply a sheet of brass track board with 5 watt resisters to adjust the voltage .. very easy to build.and cheap compared to the electronic variety. There is one drawback in that except at the ‘off’ position one is drawing full current off the battery .. but my models are big enough to have big batteries to which this is not a problem in practical terms.

I would have thought that the idea was to not have bad connections in any circuit and paraleling the batteries merely increases capacity and a single battery could provide the feared ten amps in the wrong’ situation.
22 July 2008 at 18:01 #14806
60watt
Participant
@60watt
Hello JC,

Although I quoted your post of the previous evening,my post of 17:29 on the 21st was really directed to Dan (Fatcat) to caution him not to follow your suggestion of connecting drive batteries together.

In his twin throttle drive,such a connection would create a negative ground loop )or a parallel connection from receiver ground to the drive battery ground).

Apart from increased interference there is the possibility of the full motor drive current passing from through the servo cables and plugs(black wires) of each speed controller,through receiver negative rail and through the thin signal ground tracks inside the speed controllers.

I’ve seen it happen twice.It melted off insulation of the servo cable negatives,welded a servo plug to receiver and fused open the copper circuit board track on one speedo.

My inference from Fatcat’s first post in this thread is one 7.0 Ah battery for port and one for starboard.In such a case there is no increased capacity to be gained by cross connection.

Tom
31 July 2008 at 12:23 #14984
Dan Walker
Participant
@danwalker
Right, i think i might just leave them as they are then as theres talk of things welding together etc. ive had a play in the pond with the current setup and have had one blown fuse due to a friggin empty bread wrapped which stopped the motor dead. no damage to other components.

Thanks for the advice.

Dan
9 January 2009 at 19:20 #1652
Dan Walker
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@danwalker
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