Print

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

[kiwimodeller]

My Steam Picket boat has a 4 cell 4.8v NiMh pack to operate the servos which control the rudder and throttle and reverse the steam engine. I have recently acquired a sound module which a friend is assembling for me from a kit. Two problems have arisen - the first that the module needs 12volts (but very low amps) and the second is that the module is operated by a push button switch. I could get around the second problem by installing a micro servo to operate the switch as I have spare channels on the R/X but I was wondering if it was possible to wire the module to the R/X? As for the voltage I need a way to have 12v for the module and no more than 9.6v for the R/x. I would have room in the cabin for another small battery pack but not for an SLA. If possible I would like to stick with NiMh or similar but I would consider changing to Lipo if I had to. Whatever I use I will need a suitable charger unless a 12v SLA charger or my Hi Tec CG 325 multi voltage charger could be used.as my present. Any help to get this working would be much appreciated. Thanks, Ian.

[malcolmfrary]

NiMH AAA batteries are generally available. 10 cells for 12 volts. SLA is not the only battery technology capable of giving 12v.  Or run the entire system from a 12 volt battery and use a UBEC to supply the 5 volts for the parts of the system that need it.
Without knowing the size and shape of the model and what the sound unit is and what it is intended to do, there is a lot of guesswork.
The switch can be replaced by the contact of a switcher which does the job of a servo plus microswitch.
Most audio amps will run on reduced voltage but usually at reduced power.  Sound power out is directly related to electrical power in (no free rides), so generally, little power in gives little sound out.

[Bob K]

If space and/or weight is a problem you might like to consider a small 9V PP3 battery, the press stud terminal type.  Not quite 12V but may be enough to run your sound system amplifier.  At around a Fiver worth trying.

[kiwimodeller]

Thanks for the suggestions gents. Excuse my ignorance Malcom but what is a UBEC? Could you perhaps post a link to show me what they do and also the Switcher. A suggestion on where do get them would also be of value. I had thought that the idea might be to run a 12v pack of AAA NiMh's and then use a step down of some sort to run the R/X and servos. Is this what the UBEC does? When the unit is assembled I will try it on a 9.6v pack as I have one of those in another boat. That would be the easy way out as I have battery packs and a charger and my R/X is rated for that but if the sound is not good I will look at getting a 12v pack made up and use the UBEC to power the R/X. Cheers, Ian

[malcolmfrary]

It is a Battery Eliminator Circuit.  But importantly, unlike "ordinary" BECs, does not regulate by losing power as heat, but acts more like the speed controls that we have all been using the last quarter century.  This effectively means that the usable power out of it is almost what goes in, without the heating problems of earlier linear BECs.  Regulating to a lower voltage than the source is always easier than trying to get a voltage increase from a low voltage battery.
Lots more info here after a quick google - http://www.wattflyer.com/forums/showthread.php?t=39138

It would help to know what the sound unit is going to be doing - something continuous like a motor sound can often use more power than the motor driving the boat, and needs a battery capable of handling the current.  Occasional sound at a higher pitch is much less demanding.

[kiwimodeller]

Thanks again, the module will only be making the two chime steam whistle sound. As soon as my friend has assembled the kit I will get the literature back and check what the current draw is but from memory it is less than 1 amp. It was the need for 12 volts that was worrying me but I will try it on 9.6v first. If all else fails I will make up a ten cell AAA NiMh pack and feed the module separately using an extra servo to turn on and off the module switch mechanically.  Cheers, Ian.

[malcolmfrary]

For something like an occasional whistle, if the 9 volt battery doesn't do the job, one of these - http://www.toolstation.com/shop/p92000?mkwid=s1IRXIKrA_dc&pcrid=46305642023&pkw=&pmt=&gclid=CIX7oIOM6cwCFYIK0wod_1QMuw - might.  Remembering to turn it off between sessions would be important - even a trickle taken by an amp just sitting there doing nothing does add up. 
If the amp does not have an electrolytic capacitor connected across its power input, fitting one of about 1000μF will help overcome any shortcomings of a low amperage battery.  Quite often, just turning the wick up a bit on the volume control makes up for volume lost due to low voltage, as long as that voltage is stable enough.  Nothing should be too critical, it isn't Hi-Fi.

[kiwimodeller]

Great, thanks for the help, will do a post when I get it working. Cheers, Ian.

[Netleyned]

Steam Engine, why not a steam whistle?


Ned

[malcolmfrary]

Nobody can hear a scale steam whistle.  Physics & resonant lengths.

[kiwimodeller]

Ned, many reasons - I was given the kit, there is not much room for a vertical steam whistle in the right position, there are no more threaded fittings in the steam dome and I just wanted to try it out as a couple of my other boats already have real steam whistle. Malcolm, if we cant hear it I will see if I can source some scale ears! Cheers, Ian.

[inertia]

Ian
I found this while looking for something else - and thought of your steam whistle. http://www.componentshop.co.uk/11-1v-350mah-20c-continuous-discharge-lipo-battery.html
It weighs barely more than an ounce and has all the power your whistle module would need.
Dave M

[kiwimodeller]

Thanks for the link, it does look like it will do the job but I would hesitate for two reasons - the first being that I have no experience with Lipos but understand you need to have a special charger and a bag to put it in while charging. The other problem is getting it, if you look at the shipping tab on the web page it says they cannot be posted. I will try local suppliers but will try the easy route with a 9.6v or a NiMh pack first. cheers, Ian