Today I bought an LED bulb from a local shop that starts with T and ends in O it's one of there own brand according to its packaging it should consume 9 watts and give the same light as a real 60 watt bulb. Anyhow I took it to my shack a to test how much RFI it made I was pleasantly surprised that it only seemed to give a little rectifier noise on the higher bands name 15 and 10 meters. The noise disappeared completely when I connected my digital multimeter on AC volts between the metal lamp base and earth just to see how much leakage voltage was on the metal base it was around 11 volts one way and around 8 volts the other way polarity reversed by swapping the supply wires. Next I thought ide try the lamp on DC not expecting it to work but surprise surprise it worked fine fed with around 230 VDC from a full wave rectifier it worked fine pulling around 27 mA adding a capacitor for a bit of smoothing gave 330 VDC and the lamp remained lit for a couple of seconds while the cap ran down. Final test was running it on AC of 240 volts it took 70mA from the mains I will re check the figures tomorrow as I don't get why there would be the difference in current. Finally after running the lamp for around 40 minutes the plastic base of the lamp was too hot to touch other than that it seemed fine
Almost all of these lamps use DC internally, the mains is rectified by a full wave bridge and then somewhat smoothed with a reservoir capacitor. Therefore DC input will be fine.
The OPTIMUM DC input is generally higher than the RMS AC input. This is because the internal DC voltage within the lamp tends to approach the peak of the of the AC mains, rather than the RMS figure.
OTOH, many of these lamps work over a very wide range of input voltage.
The wattage input should be roughly constant at any voltage AC or DC on which the lamp works correctly. The current input will be a lot higher on AC than with DC. This is because on an AC supply the input current will be very peaky.
Consider as an example, that the internal capacitor charges to 320 volts. Current will only flow into this capacitor when the momentary voltage of the mains exceeds 320 volts, this is only for a small part of each mains cycle. Therefore a relatively large current must flow for this small part of the cycle.
Thanks Broadgage tomorrow il try it over a wider range of AC input volts just to see what range it will work over. I was surprised at the difference in its current on DC and AC I will try to set up my scope so I can look at the input waveform il let you know how I get on!
On AC you'll have power factor to contend with - from those numbers it sounds like it'll be worse than 0.5 - with DC there's no such thing as power factor so the current draw should be 'flat' as it were.
There again your AC current meter is probably making all kinds of assumptions when converting the instantaneous currents its sensing (which will vary from millisecond to millisecond as the AC waveform moves along) to a single value to display - probably assuming that the current is a pure sine wave - while in practice it's likely to be anything but.
If the lamp is only intended for 220 volt to 250 volt circuits, then it should operate down to about 190 volts. That allows for a nominal 220 volt supply that is at the lower limit of 90%, or 198 volts actual, and a few volts lost in the consumers installation.
If the lamp is intended for USA or European supplies, then it should operate down to about 100 volts, or a nominal 120 volt supply at the lower limit of 90%, or 108 volts actual, and again allowing for drop to below 108 volts within the premises wiring.
If for true worldwide use, then it should work down to about 85 volts, to allow for Japanese 100 volt circuits.
BTW, ELV LED lamps are also available with a wide operating voltage range. I have some intended for 10 volts to 30 volts, DC. Suitable for nominal 12 volt systems with a low battery and some voltage drop in the wiring, or for 24 volt systems with the battery on boost charge. Or indeed for nominal 16 volt systems if any such remain in use.
If the lamp is only intended for 220 volt to 250 volt circuits, then it should operate down to about 190 volts. That allows for a nominal 220 volt supply that is at the lower limit of 90%, or 198 volts actual, and a few volts lost in the consumers installation.
If the lamp is intended for USA or European supplies, then it should operate down to about 100 volts, or a nominal 120 volt supply at the lower limit of 90%, or 108 volts actual, and again allowing for drop to below 108 volts within the premises wiring.
If for true worldwide use, then it should work down to about 85 volts, to allow for Japanese 100 volt circuits.
BTW, ELV LED lamps are also available with a wide operating voltage range. I have some intended for 10 volts to 30 volts, DC. Suitable for nominal 12 volt systems with a low battery and some voltage drop in the wiring, or for 24 volt systems with the battery on boost charge. Or indeed for nominal 16 volt systems if any such remain in use.
The 120v US supply has a tolerance of 5%. Thus minimum is 114v.
Yes, I know that USA mains usually has a tolerance of 5%. Nevertheless it can in practice be 10% low. In rural areas the supply may be to a post at the boundary of the property, with a potential loss of another 5% in the customer owned cable into the house.
And of course USA type electricity is used in other places with less strict voltage regulation. In parts of South America, anything over 100 volts is good.
Hi all I've done. Some more tests on my LED lamp firstly the current taken from the AC mains is 70 or 73 mA depending on which meter I look at. Secondly at 240 volts it consumes 9.6 watts this remains constant until under 100 volts current consumption gradually rises to 113 mA as volts are decreases down to around 95 volts when it drops back to around 70 mA then rises again down at 70 volts the lamp flickers then goes out. It's brightness is virtually constant from 100 to 250 volts there is a slight dimming below 130 volts but it's very slight it is rated for 220 240 volts but is ok over a much bigger range
