Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Southern Sailor on August 04, 2019, 08:25:35 pm
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Could someone please tell me what current a grain of wheat light bulb draws? Thanks. Brian
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A quick check online suggests 80ma for a 12v version.
Colin
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Thank you Colin. I will be running off 12V but it seems that doing so will shorten the life of the bulb so I will reduce that to say 9V. I assume a simple resistor will do the trick. Oh dear these electronics - not my strong point! Happy sailing. Brian
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Hi I did a quick envelope calculation and you want a minimum 1 watt resistor value 180 or 220 ohms. One for each bulb. Not critical but if the resistor is too small in size it will get hot and burn out.
It might be worth trying 2 bulbs in series to see if they are sufficiently bright?
You could buy 6 off AAA dry cells and they will run for a long time but depending on number of bulbs.
Another solution is to buy a voltage reducer unit suitable for 12 volts input and adjustable output. They have a button function to adjust o/p voltage and an LED readout of output voltage.
I think someone posted about these units previouly, but I have never used one. They are not dear less than a fiver and will run a lot of bulbs.
regards
Roy
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Using a calculator rather than the envelope, to lose 3 volts at 80mA, a 37.5 ohm resistor is needed, rated at about 0.5 Watts. Nearest readily available values are 33 ohms or 39 ohms. 39 is probably preferable. One per bulb.
Running 12 volt bulbs on effectively 9 volts will make them last much longer, but they will run fainter.
Just to add confusion, they do come in a range of voltages - [size=78%]https://www.ebay.co.uk/itm/291657153591 (https://www.ebay.co.uk/itm/291657153591)[/size] - but require very much the same current.
You could use a forward only speed control (should be rated for 12 volts) driven by a servo tester (powered from the BEC hopefully in the ESC) as a controlled voltage source.
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OOPs sorry about that I got a bigger envelope and it worked out as Malcolm has said.
How many bulbs are you operating?
regards
Roy
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Instead of resistors much better to use a buck dc to dc convertor to lower the voltage, they are cheap
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Instead of resistors much better to use a buck dc to dc convertor to lower the voltage, they are cheap
Like these?
https://www.amazon.co.uk/LM2596-Converter-3-0-40V-1-5-35V-Supply/dp/B01GJ0SC2C?ref_=fsclp_pl_dp_3
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Gentlemen thank you for your help. I have 9 bulbs on the Portgarth mast. I'm switching them by an electronic switch activated by channel 5 or 6 on my transmitter. I have planned to use the mast itself as the negative and bring the positive leads down into the deckhouse. Hence they are planned to be all in parallel. While this does increase the current drawn it also avoids all bulbs going down if one fails.
However, from what you have said, there is merit in using a buck converter to reduce the voltage. I did think of grouping them into three parallel groups of 3 in series in each group but the buck converter can drive them all in parallel and will take care of reducing the voltage. I need to make sure that the electronic switch can handle the buck converter and the current for all 9 bulbs. Will post the final solution and perhaps a photo. Thanks again. Brian
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I never heard of a "buck" converter until I checked that link but doesn't component shop or model radio workshop make a 4 or 5 channel switcher exactly for this? Think I did it really easy before with an action switcher but they're defunct now.
Rich
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I have ordered 12 post free for under a tenner and not from China.
Regards Howard
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Thank you Colin. I will be running off 12V but it seems that doing so will shorten the life of the bulb so I will reduce that to say 9V. I assume a simple resistor will do the trick. Oh dear these electronics - not my strong point! Happy sailing. Brian
Get a rechargable PP3 battery, 9v right there.
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Get a rechargable PP3 battery, 9v right there.
9v but not for long running several bulbs in parallel. 9 at 75mA each equals nearly 700mA, not something that a PP9 can sustain for more than a very few minutes.
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9V PP3 is normally 110 or 150mah so quite right, not going to last long. 10 mins ma @ 700mA
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9v but not for long running several bulbs in parallel. 9 at 75mA each equals nearly 700mA, not something that a PP9 can sustain for more than a very few minutes.
Nah, you can get two 600mah rechargeable Li ion PP3 for a tenner. That's nearly 2 hours use swapping one out for the other given the draw you have stated.
https://www.ebay.co.uk/itm/Genuine-EBL-2-4-6-8-pcs-9V-600mAh-Rechargeable-Li-ion-PP3-6F22-Battery-UK-STOCK/153505205743?hash=item23bd9f8def:m:m0X4dtXyta7LE2lpuBjwpIw
Admittedly Im running 6 leds which have a lower current draw, on one such PP3 in my heli and it lasts.
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Nah, you can get two 600mah rechargeable Li ion PP3 for a tenner. That's nearly 2 hours use swapping one out for the other given the draw you have stated.
https://www.ebay.co.uk/itm/Genuine-EBL-2-4-6-8-pcs-9V-600mAh-Rechargeable-Li-ion-PP3-6F22-Battery-UK-STOCK/153505205743?hash=item23bd9f8def:m:m0X4dtXyta7LE2lpuBjwpIw (https://www.ebay.co.uk/itm/Genuine-EBL-2-4-6-8-pcs-9V-600mAh-Rechargeable-Li-ion-PP3-6F22-Battery-UK-STOCK/153505205743?hash=item23bd9f8def:m:m0X4dtXyta7LE2lpuBjwpIw)
Admittedly Im running 6 leds which have a lower current draw, on one such PP3 in my heli and it lasts.
....but he's getting 12 of the regulators, each one of which will do the job, for under a tenner. It looks like modern technology has come up with something genuinely useful. Costs less, does the job, simpler to use that the traditional solutions.
The link shows one PP3 for a tenner, so that becomes £20 for two, but doesn't mention the appropriate charger.* I can't help but feel a bit of uncertainty about Li-ion 9 volt batteries - the chemistry just doesn't allow for actually hitting 9 volts. If it is 3 cells internally, that is over 11 volts, which could well not be good in many uses, in this case offering more volts than wanted thus negating any value of not running directly off the main 12 volt battery. The adjustable regulator also allows the brightness to be adjusted to suit the users preference.
How sensitive are Li-ion batteries to over discharging?
I used to run the nav lights on my small tug (3 LEDS in a series chain with a liniting resistor and bypass resitors to even the current) which drew 15mA, and a non rechargeable PP3 used to last over two seasons sailing.
*there is one on the link under the "related items", £8.99.
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I would run LED's, they last a lot longer and use much less current and run them off the 5 volt receiver bus, that way you have a nice regulated voltage.
Try 130-200 ohm current limiting resistors for each LED. That will limit current to around 15ma per LED.
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Think I did it really easy before with an action switcher but they're defunct now.
Rich
Which ACTion unit is that, Rich? All of the switchers which were available twelve years ago are still available now, although the single and twin relay ones are to be updated with SMT components. The P62 Quadswitch will operate four totally independent relays selectively from just one RC channel. https://www.componentshop.co.uk/p62-quadswitch.html (https://www.componentshop.co.uk/p62-quadswitch.html)
DaveM
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....but he's getting 12 of the regulators, each one of which will do the job, for under a tenner. It looks like modern technology has come up with something genuinely useful. Costs less, does the job, simpler to use that the traditional solutions.
The link shows one PP3 for a tenner, so that becomes £20 for two, but doesn't mention the appropriate charger.* I can't help but feel a bit of uncertainty about Li-ion 9 volt batteries - the chemistry just doesn't allow for actually hitting 9 volts. If it is 3 cells internally, that is over 11 volts, which could well not be good in many uses, in this case offering more volts than wanted thus negating any value of not running directly off the main 12 volt battery. The adjustable regulator also allows the brightness to be adjusted to suit the users preference.
How sensitive are Li-ion batteries to over discharging?
I used to run the nav lights on my small tug (3 LEDS in a series chain with a liniting resistor and bypass resitors to even the current) which drew 15mA, and a non rechargeable PP3 used to last over two seasons sailing.
*there is one on the link under the "related items", £8.99.
Yes, that's fair enough, different strokes for different folks. I just offerred an alternative off the shelf option which is simple, needs no work and doesnt have 12 points of failure.
Whatever floats everyone's boat. :-))
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Which ACTion unit is that, Rich? All of the switchers which were available twelve years ago are still available now, although the single and twin relay ones are to be updated with SMT components. The P62 Quadswitch will operate four totally independent relays selectively from just one RC channel. https://www.componentshop.co.uk/p62-quadswitch.html (https://www.componentshop.co.uk/p62-quadswitch.html)
DaveM
...Sorry Dave, think I probably meant "Hunter Systems" being not available now rather than ACTion. I can picture the unit I have in my mind, but not anywhere near to check! Of course, I'd still make a personal recommendation for ACTion and Model Radio Workshop. And for a few tiny bulbs I'd just use a separate small battery or a few tiny resistors -KISS, but appreciate it's not always that way these days.
Rich
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I have installed the DC-DC converter as shown. The photo also shows two electronic switches feeding control boards one for the radar motors and one for lighting. Sorry about the untidy mess but wiring still needs to be finalised and connected up. Brian
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Hi Gents,
Just to say my 12 arrived this morning £9.97 posted only ordered them very late Wednesday night so really just three days very pleased. cant see me ever needing any more 12 boats is enough for any one.
Regards Howard
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I have ordered 12 post free for under a tenner and not from China.
Regards Howard
Hi Howard
Sorry to ask but could you please post a link, as I am in the need of some.
Thanks in advance
Fred
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Will try Fred as I don't know how. http://www.ebay.co.uk/itm/312701076422 try that Regards Howard
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Hi Fred the price is £9.79 for 12
Regards Howard.
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Hi Howard
Thank you for the link, have just ordered some.
Thanks again
Fred