Plataformas y soportes digitales

to the ozone gas quickly heals skin wounds and rashes. You may apply ozonated olive oil to speed up healing.

There are may other uses of ozone which one can try. The gas should not, however, be inhaled directly, continu-

ously. ❑

Readers queries:

❑ I would like the authors to clarify the following points, which are not covered in the article:

1. On which terminal of the LOT (2070/2095) are the primary wires ter- minated by jumpers, i.e. which pins are connected to D10 and R13/R14 (parallel combination)?

2. Though EHT pin of the secondary is connected to the outer aluminium foil on discharge tube, what is the EHT pin number and where is the ground pad for aluminium tube to be connected (using the jumpers)?

3. What is the total power consump- tion of the unit at full capacity?

4. What is the air-pump capacity in litres/minute to get the ozone output of 4 mg/litre, as stated in the article?

5. Since I will be using the ozone unit of the project from 230V AC mains, what changes are required in the circuit (Fig.2), like in the values of R7, R8, C4, C5, etc. Using 120V-150V source is not possible, as the use of 120V AC will require a sepa- rate auto-transformer.

6 . T h e r e i s l i k e l y to be heavy electrical

interference with TV and even a PC (since the main supply is same) when the corona discharge takes place. Is it possible to suppress it effectively? EHT capacitors are avail- able up to 20kV rating,

but they cost Rs 750 to Rs 800 and hence are uneconomical to use. Kindly sug- gest some alternative method to reduce interference.

P.P. Damkevala Industrial Electrical & Electronics Mumbai ❑ I need a few clarifications regarding the

instead of an aluminium pipe?

3. What should be the thickness of the glass?

M. Selwyn Doha (Qatar) ❑ 1. Please explain how to remove EHT diode from the EHT transformer supplied by Kits‘n’Spares.

2. As per the text, the portable ozo- nator can work at 120V continuously for four hours, but during trial we observed that it is not working at 120V, and needs 220V to work. However, within 5 to 10 minutes of operation, resistances R8, R14, R15 get heated. Please clarify.

3. The ozone control potentiometer (VR3) is not found to be working. When we increased VR3 for ozone control, some smoke came out from the kit and the cir- cuit stopped working.

We want the ozonator to work continuously for 4-6 hours as per the text.

EFY

The author, Prof. K. Padmanabhan, replies:

1. In my (original) circuit using LOT 2070, pins 2 and 6 were wired to the re- sistor (substituted in Fig. 2 by a parallel

combination of R13 and R14) and diode (BA159) respectively. For 2095 LOT, EFY may offer its comments.

2. The EHT cable comes out of the LOT as a red high-voltage wire. The aluminium tube is grounded to pin 6 of LOT 2070.

3. The full power may be 10W to 15W. 4. The air pump gives 3-4 litres of flow per minute. We used aquarium air pump.

5. With 230V mains, the rating of the unit is just below 3 minutes. R8 was 82-ohm/1W (in original circuit); R7 is the

colour TV kept in the same room. If in- terference is noticed, one may use a sim- ple LC circuit for mains feed, as shown in Fig. 1 here. Inductor L is wired on a small ferrite core with 8 turns of 22SWG wire, and each capacitor (C) can be rated 0.01µF, 600V.

Regarding M. Selwyn’s query:

1. Power is 230V only. 2. Yes, stainless steel is better. 3. Glass thickness should be small, say 2mm.

EFY: We had to modify the original circuit slightly as the components (wire- wound resistors) were getting overheated. The modified circuit was tested at EFY Lab for four hours continuously without any such sign and proper ozone output was observed as indicated by the space current. The transformer stamped ‘2070’ procured by us from local market did not have a separate EHT (only) potted limb. We could get a Leader brand dual-limb EHT transformer (No. 2095) which gave the rated EHT at about 160V AC itself and not at 230V AC. Please note that in most CTVs the horizontal output section feeding the EHT primary employs a supply voltage of 110 to 165V DC. It is therefore obvious that in most EHT transformers the peak primary voltage is limited to 160V (at line frequency of 15,625 Hz).

In Leader brand transformer ‘2095’ used by us, the EHT section (potted) had 3 wires (red, blue and white) going to some of the pins on the base, which we de- soldered from the base and used them as explained below, after checking the resist- ance amongst them:

(a) Blue and red (EHT primary, 25 to 30 ohm). This primary pair was connected to cathode of D10 (BA159) and R13/R14 (loose-end in Fig. 4 in the article, i.e. com- ponent layout) respectively.

(b) White and the EHT diode bottom

Fig. 1: Simple LC circuit for mains feed

and R16 goes to inner aluminum tube in Fig. 1. EHT diode bottom end is the EHT (AC). It is connected directly to aluminium foil (HT electrode in Fig. 1). Please note that to gain access to bottom end of EHT diode one has to carefully remove it after cutting insulation with hacksaw blade.

If you want to use a ready-made EHT transformer with 230V AC, you have to use a step-down auto-transformer to get 110V to 160V AC. Else you may have to approach a willing manufacturer to double the EHT primary turns to operate it with 230V AC.

EFY: The EHT transformer has been supplied (by the manufacturer to Kits‘n’Spares without EHT diode, at our behest) after doubling the primary (tunable) windings. Since the primary windings have been doubled in this EHT transformer, the circuit is capable of working

with 230V AC primary directly. Earlier we had tested the assembled kit for just about an hour without any problem. However, when we tested the circuit again, after receipt of your letter, the same worked satisfactorily for half an hour and then suddenly resistors R13 and R14 started smoking. The problem was analysed and it was concluded that the reflected noise spikes from EHT secondary to primary due to higher level of corona discharge, was reaching the MOSFET via the AC mains line, which eventually damaged the MOSFET (shorting its drain and source) with consequent burning of the mentioned components.

This problem was solved by connecting a MOV (metal oxide varistor RDN 240/20 of ELPRO make) across the input AC 230V terminals. We are forwarding the required quantity of varistors @ one per kit to help you rectify the problem. With this modification

we have run the ozone generator for over five hours with improved performance and no problem whatever.

As regards the ozone control potmeter, it varies the low frequency modulating stage duty cycle and does have a limited effect. If you want to have a higher span, you may replace VR3 (1k) with a 2-kilo- ohm multiturn wirewound potmeter (cer- met for smoother control). The damage, in your case, could have occurred due to make-break of the wiper contact during its manipulation.

Kindly note that the projects published in EFY do not necessarily mean that the circuits can be straightaway adopted for production/commercial use without fur- ther improvement or development. These are in fact meant for hobbyists/electronic enthusiasts. If these are to be commercially exploited, some amount of development ef- fort may be necessary.