I purchased this to try out in my next Blunami install. 18 VAC in and got 24 VDC out. I'm waiting on a speaker to do the install.
Todd
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Please post details and pictures as you progress!
I've used similar items for other purposes, such as adding smoke units. One question - how do you adjust the output voltage? The units I use have a small adjustment screw; I didn't see one in the pictures.
@Mallard4468 posted:I've used similar items for other purposes, such as adding smoke units. One question - how do you adjust the output voltage? The units I use have a small adjustment screw; I didn't see one in the pictures.
That is NOT a voltage regulator, just a rectifier and capacitor filter.
The voltage out is directly tied to voltage in with no adjustment. The output voltage difference is easily explained by AC RMS input VS Peak rectified voltage output- especially under light to no load conditions. RMS is less than peak voltage- it's the average on the AC waveform. Again under no or very light load, the capacitor will charge to at or near peak voltage hence the difference- 18V AC RMC VS 24V DC Peak voltage. I might add- this is how you can blow up electronics- hitting them with a high peak voltage- higher than they are rated for.
If you need a lower voltage, you need 3-4 functions in the circuit- rectify AC to DC, then bulk filter capacitor to get pure high voltage DC, then regulate down the voltage, and possibly more final filter (caps).
As an example- way more steps and components
@Vernon Barry posted:That is NOT a voltage regulator, just a rectifier and capacitor filter.
The voltage out is directly tied to voltage in with no adjustment. The output voltage difference is easily explained by AC RMS input VS Peak rectified voltage output- especially under light to no load conditions. RMS is less than peak voltage- it's the average on the AC waveform. Again under no or very light load, the capacitor will charge to at or near peak voltage hence the difference- 18V AC RMC VS 24V DC Peak voltage. I might add- this is how you can blow up electronics- hitting them with a high peak voltage- higher than they are rated for.
If you need a lower voltage, you need 3-4 functions in the circuit- rectify AC to DC, then bulk filter capacitor to get pure high voltage DC, then regulate down the voltage, and possibly more final filter (caps).
As an example- way more steps and components
Thanks. That's what I was thinking - I got it right for once!
That 4700µF capacitor is big enough to handle any reasonable loco motor load - arguably overkill for typical motors. You can place a DC>DC converter (used as a regulator) to drop the voltage down to 18-21 VDC for Blunami powering. Do note that using the rectifier/filter as-is gets you close to the maximum input voltage rating of the Blunami card, with typical track voltages (18-19V) and when the engine is idling. That leaves little headroom for surges, which is why I recommend using a switching converter/regulator between the rectification/filtering and the Blunami card. The Blunami will provide a warning if input voltage is high, but Murphy's Law holds that a voltage surge will happen when you're not nearby and unable to react. Fitting all of this into a Geep hood gets interesting.
A simple bridge rectifier and filter such as this device, will charge the cap to the peak of the voltage, 18 V in X 1.414 = 25.2 volts DC. Remember that AC is given in EMF or a DC equivalent, even your 120 volt wall outlet, since both halves of the cycles are there with no rectification, you have 120 X 2.828, or 340 volts peak to peak at the outlet. When you load this supply, assuming you feed it with 18VAC, it will drop to as low as 12 volts and be very ripply. A bridge rectifier with no filter will supply .707 time EMF volts, in this case 12 volts from 18VAC in. Of course a regulator will help with voltage stability, but if you load this unregulated supply and you get a usable voltage with acceptable ripple they work fine. You can also add more capacitance to smooth the DC more, but there is always a trade off based on just how much current you need, and whether you need it fairly pure for things like audio. Normally a good regulated supply with smooth DC out, requires an minimum 18 volt transformer to get smooth 12. Switching supplies are another animal altogether. An analog supply with linear regulator of say 12 volts at 5 amps is a fairly large thing, but as a switcher supply, 12V at 5 amps can be the size, and weight almost, of a pack of cigarettes.
