Current Draw on 5v/19v/24v Light Bulbs - myLargescale.com > Community > Forums


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Old 03-23-2020, 08:30 AM   #1 (permalink)
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Default Current Draw on 5v/19v/24v Light Bulbs

Can someone provide me and all Forum users the current draw for 5 volt, 19 volt and 24 volt light bulbs used in LGB locomotives. I'm installing a Soundtraxx DCC Sound Decoder which has the following light/function specification limitations: 12 volts/100 mAmp each function output. I'm going to switch the existing three 5 volt lamps to 19 volt lamps.
5 volt bulb current draw:
19 volt bulb current draw:
24 volt bulb current draw:

Thanks
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Old 03-23-2020, 11:11 AM   #2 (permalink)
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Which specific Soundtraxx decoder are you planning to use?


If the maximum voltage the function output can handle is 12 volts, then you would need an external device to switch the 19 volt lamps anyway so that the actual current draw of the 19 volt lamp is not that important.


If I remember right, LGB specified 50ma for the 5 volt bulbs and 40ma for the 19 & 24 volt bulbs. But for incandescent bulbs you also have to consider the inrush current.
And why change to 19 volt incandescents at all?
There are LED equivalents for the 5 volt LGB bulbs that are straight replacements that you could use which would use less current than incandescents and they don't have that higher inrush current.
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Old 03-23-2020, 09:18 PM   #3 (permalink)
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Quote:
Originally Posted by krs View Post
Which specific Soundtraxx decoder are you planning to use?


If the maximum voltage the function output can handle is 12 volts, then you would need an external device to switch the 19 volt lamps anyway so that the actual current draw of the 19 volt lamp is not that important.


If I remember right, LGB specified 50ma for the 5 volt bulbs and 40ma for the 19 & 24 volt bulbs. But for incandescent bulbs you also have to consider the inrush current.
And why change to 19 volt incandescents at all?
There are LED equivalents for the 5 volt LGB bulbs that are straight replacements that you could use which would use less current than incandescents and they don't have that higher inrush current.
Hi - I'm planning to use the Soundtraxx Tsunami2 TSU-2200 which has a 2 amp capacity which should be okay for this small LGB 22604 Schoema Diesel locomotive. Per the Soundtraxx installation instructions, if using lower voltage light bulbs less than 12 volts, must add resistors. So I just bumped the bulbs up to 19 volt units and they work fine with the decoder. Alternatively, I could replace the bulbs with LEDs which use very minimal current. Do you think the 2 amp decoder is sufficient.......if not I'll have to use their 4 amp Tsunmai2 decoder?
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Old 03-23-2020, 10:39 PM   #4 (permalink)
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The Soundtraxx Tsunami2 TSU-2200 is actually not a 2 amp decoder in the way other DCC decoders are rated.
For some reason Soundtraxx still uses the stall current rating, every other decoder manufacturer I can think of uses the continuous current rating plus sometines a 20 second peak current rating.
The stall current rating is typically at least twice as high, often even higher than the continuous rating of the same decoder.
So I would conside the TSU-2200 an 0.8 - 1.0 amp decoder suitable for H0 scale and maybe for a very small LGB loco like the Field Railway locos which would only pull a few small cars.
Soundtraxx recommends this decoder for H0 to S gauge, so I would image they would not honour any warranty if you use it in a G-Scale loco.
But you could always ask them and see what they say.
Or just ask them what the continuous motor current rating is and also what the total current rating of the decoder is - ie including all function outputs.
On many decoders the motor current available has to be de-rated by the function output current.
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Old Yesterday, 07:05 AM   #5 (permalink)
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I use the Zimo 1.2 amp MX645 in single motor LGB engines. This is total current (lights, motor, etc.). Never had a problem with more than 6 engines I have installed this decoder in. Also there is a MX645P22 version that is rated at 1.8 amps total. Note that peak current is 2.5 amps on these and over 30 volt surge tolerated.
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Old Yesterday, 10:44 AM   #6 (permalink)
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Quote:
Originally Posted by krs View Post
The Soundtraxx Tsunami2 TSU-2200 is actually not a 2 amp decoder in the way other DCC decoders are rated.
For some reason Soundtraxx still uses the stall current rating, every other decoder manufacturer I can think of uses the continuous current rating plus sometines a 20 second peak current rating.
The stall current rating is typically at least twice as high, often even higher than the continuous rating of the same decoder.
So I would conside the TSU-2200 an 0.8 - 1.0 amp decoder suitable for H0 scale and maybe for a very small LGB loco like the Field Railway locos which would only pull a few small cars.
Soundtraxx recommends this decoder for H0 to S gauge, so I would image they would not honour any warranty if you use it in a G-Scale loco.
But you could always ask them and see what they say.
Or just ask them what the continuous motor current rating is and also what the total current rating of the decoder is - ie including all function outputs.
On many decoders the motor current available has to be de-rated by the function output current.
krs - Thanks for your insightful response. I've asked Sountraxx Technical Office in the past whether their Soundtraxx Tsunami2 TSU-4400 series sound decoders, rated at 4 amps max, could handle an LGB two motor locomotive. They always respond back to me to measure the Stall Current of the locomotive to determine it myself. So, you're right, they keep using Stall Current as their baseline which isn't very helpful. Since I'm going to sell the LGB Schoema locomotive on eBay to a customer, I'll play it safe and use the 4 amp Tsunami2 TSU-4400 series sound decoder instead of the 2 amp Tsunmai2 TSU-2200 series decoder. I did, however, install the TSU-2200 into an LGB Olomana recently and it works great which a friend of mine did measure it only draws about .7 -.8 amps.

Dan - Thanks also for your response. Sounds like the similarly-rated Zimo decoders are more robust than the Soundtraxx units.
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Old Yesterday, 11:07 AM   #7 (permalink)
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Tom - You can actually measure the stall current of any motor fairly easily with a good Ohm-meter that measures low resistance accurately.
Just measure the resistance of the motor (windings) and then use Ohm's law, I = E/R with "E", the DCC voltage.
Years ago, when the stall current was still a "thing" with DCC decoders, we measured the actual stall current of G-Scale locos with a scope and also using the resistance measurement and Ohm's law and the results were the same.
The tricky part is to get a meter than measures low resistance accurately. And don't forget to subtract the resistance of the test leads - on one of my meters I just checked, their resistance is 0.8 ohms.
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Old Today, 07:03 AM   #8 (permalink)
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In regards to my post, Zimo does publish a lot of info about their decoders,Max voltage/surge voltage and 20 second time, max current/surge current.
And remember a decoder current rating can be all factors motor, lights, smoke, servo current draw all added together!!! This is what zimo does.
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