[Stoves] Dhan Hurley..... TLUD enhancements.... Why aren'tthereany comments, except from what it seems is a Venture Capital Company?

[Crispin Pemberton-Pigott]

Dear Friends

 Single battery garden lamps have an NiMH battery with a voltage not high enough let the LED start. Once the current flows having overcome the forward voltage drop, the current can continue to flow. They are after all, current devices, not voltage devices. They done care what the voltage is once started.

There is a very small circuit on the board that creates a small flow of current through a tiny coil. Shutting off the power boosts the voltage as described by Andrew to about 2-3.5 volts which is enough to overcome the forward voltage drop of the LED (usually 2 to 3.5 v). The HE-LEDs are high.

Once the current flows the voltage can drop to almost zero - close to 0.2 or so, and still work. The LEDs, as I said, are current devices. Ok the current has to be limited by the supply circuit, but there is no need to boost the voltage once it is lit.

The booster in the lamp fires about once per 10 seconds, if it is dark outside. Once the current starts to flow, the booster shuts off.

Absent a circuit to initiate current flow, a hand operated boost can be used. Touch a button and induce a voltage, and the light comes on. A cigarette lighter spare? Maybe.

If you instead want to get a constant voltage output with a variable current, such as to feed a USB port, use a buck-boost to charge a phone or run a fan. These are voltage devices.

Regards
 Crispin

 VE3NLD

From: aj.heggie at gmail.com
Sent: June 8, 2019 4:29 PM
To: stoves at lists.bioenergylists.org
Reply to: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Dhan Hurley..... TLUD enhancements.... Why aren'tthereany comments, except from what it seems is a Venture Capital Company?



On Sat, 8 Jun 2019 at 06:34, Kirk H. <gkharris316 at comcast.net<mailto:gkharris316 at comcast.net>> wrote:
I have not encountered the Joule Thief before.  It appears from my search that it accumulates the low voltage electrical power, storing it in a coil, and then releases it periodically in a surge at a higher voltage.  It reminds me of a dimmer switch which passes the full power, but only in short surges.  The less time for the duration of the surge, the dimmer the light.  The Joule Thief raises the wattage to a level that it can light the bulb, but only for short surges.  Because the joule Thief is off between the surges the bulb would be dimmed and would not obtain full luminesce.  The combination of thermocouple (there is nothing wrong with combining several together as a thermopile) and Joule thief seems worth looking into for getting electricity from a wood stove.  It would be less sensitive to being overheated and damaged than a TEG.

The Joule thief was devised to get the very last bits of charge out of a single cell. As long as the voltage of the cell is initially high enough to overcome the forward voltage of the transistor in the circuit it will run and switch the current. The collapse of the field around the inductance  then causes the forward voltage spike  which is much higher than the voltage from the source and so typically  will excite an LED which has a higher forward voltage than a single cell  can provide (Lithium ion cells have a high enough voltage to light a LED without additional boosting). Once running the oscillation of the circuit  keeps the  current passing through the inductance and becomes independent of the voltage of the cell which still provided the current to sustain the device, thus it continues running until there is no charge left in the cell.

You will see these circuits in the small flashlights which only require one cell (and very effective they are too compared with incandescent torches of my younger days).

LEDs are often modulated by switching circuits and they work too many times per second for the human eye to distinguish the repeated flashes.

Andrew
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