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Marcus Wagner

Thu Sept 28 2006, 06:33AM

Registered Member #486 Joined: Sun Jul 09 2006, 01:18AM
Location: Germany/Hessen/Hanau
Posts: 9

Hello dear Group,

I am planing for a boost or pushpull converter to step up the voltage of a battery-bank (12V 46AHcar batteries) to nominal mains-voltages, to replace the mains-connection of my teslacoil system. All designs which I have found already are only for small power, but I need 240V with 2 Amps at least.

Can someone please give me a apporate place where to look or some tips at what values the inductor, capacitor, switchingfrequency and -duty should be and which topology would be best for 0.25 to 1KW?

I really need some help... ;c)

Greets,

Marcus

Dr. Slack

Thu Sept 28 2006, 07:53AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

You have several alternatives.

The first is outside your your problem as set, but I'll mention it anyway; power your TC directly from the battery, either via an ignition coil or 2, or from MOTs with primaries rewound with only a few turns. With MOTs, switch at 2x or 3x mains frequency to get 2x or 3x volts/turn, if you can power the increased core losses and think the secondary insulation can take it (oil).

Inverters. A boost type needs to store all of the transferred energy in the inductor, a transformer coupled device doesn't. So if working diorectly at mains frequency from the battery, use a push-pull transformer. Perhaps rewind the secondary of a MOT with a few turns, and get mains from the primary, as a cheap source of a 1kW low frequency transformer.

There was an article written about a year (maybe two) ago in Wireless World magazine, which was a very thorough analysis of a battery to mains convertor designed to power the author's refrigerator. The problem with this load was that while the motor needed only a few 100 watts when running, it needed 1500VA when starting, which would trip any commercial inverter he tried. His topology of boost to 350v DC rails, then invert to mains frequency, meant that the reactive power circulated only on the inverter side, allowing the boost stage to be sized for the true power. It will make usedful reading, even if its specifications do not match exactly what you want to do. I will see if I can find a reference to it.

Steve Conner

Thu Sept 28 2006, 10:56AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi Marcus,

The output of a boost converter is DC, and your Tesla coil might need 50Hz AC, if it's driven by a transformer. So you might need an inverter. You can buy them quite cheaply nowadays.

Neil: I'd be very interested to see that article too.

HV Enthusiast

Thu Sept 28 2006, 12:09PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

I am planing for a boost or pushpull converter to step up the voltage of a battery-bank (12V 46AHcar batteries) to nominal mains-voltages, to replace the mains-connection of my teslacoil system. All designs which I have found already are only for small power, but I need 240V with 2 Amps at least.

Two comments:

1. Please correct me i am wrong, but based on your description and terminology used, i am assuming you do not have much experience with switching power supplies? If my assumption is correct, then you would probably have great difficulty designing what you ask for.

2. Good news, is what you ask for are readily available for almost next to nothing. You want a simple AC inverter which can put out about 500W. You can probably get one of these for less than $100.00 USD if you shop around. Magnitudes much easier in both time and money, then building your own DC/AC inverter.

Marcus Wagner

Sat Sept 30 2006, 05:18AM

Registered Member #486 Joined: Sun Jul 09 2006, 01:18AM
Location: Germany/Hessen/Hanau
Posts: 9

Hello all,

thanks for the tips.... unfortunately I forgot to mention that I already have my (dr)sstc up and running with either 12 or 24V directly from two car batteries. The driver is a very basic one, simply an antenna feeding a pair of ucc37322&21 which drives the GDT and then a fullbridge made out of 4 2SK1488. This works quit well but not nearly as well as with the IRFZ46. With the IRFZ46 and 24V DC input I got CW-mode streamers about 10cm long into open air and about 15cm to a grounded object...

Now I want to rise the voltage without buying more batteries.

A switched capacitor based convertor seems to be the best solution as far as I can see...!???

Greets,

Marcus

FastMHz

Tue Oct 03 2006, 05:53PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

EVR's Inverter suggestion is THE way to go. Get a 12v --> 240v Euro inverter off eBay, parallel your batts, and then regulate/filter the inverter's output

Steve Ward

Tue Oct 03 2006, 10:17PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Is there some reason you cant plug the TC into the wall?

Fusion

Thu Oct 05 2006, 07:53PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

You can use an oil generator they are 1kw and cheap. If you buy an 110V you can buy a 110 to 220V transformer. Also I hear a guy used a SAI.

Sulaiman

Thu Oct 05 2006, 08:27PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Since you're using a DRSSTC I assume that what you actually need is a higher dc voltage;
if so then conceptually it's straightforward - a boost convertor.
A 555 (my favourite) or better a TL494 etc. (not my area of expertise)
driving a suitable transistor switch
(Low ON voltage at high current, voltage rating just higher than required output dc voltage)
switching an inductor.

The 'problem' is the current level (amps)
for say 300V @ 2A using a 12V battery the average battery current would be about 60A
which would mean 'continuous mode' at high frequency
for efficiency and minimum inductance requirement.

Unfortunately I've no expertise in 'continuous mode' convertors
If I did it I'd use simple discontinuous mode
which would require an inductor capable of over 150A peak before saturation!
This would mean a LARGE ferrite core operating at high frequency
or an extremely large air-cored inductor (copper tubing etc.)
Running at 24V would of course halve the currents required.

Would several 12V VRLA batteries in series be an option?
something like these

or on eBay UK item # 300027188875, (check your local eBay for equivalent)
Although low-tech it's not TOO expensive and VERY versatile for all kinds of projects
and a lot simpler to implement.

Marcus Wagner

Mon Oct 16 2006, 03:45PM

Registered Member #486 Joined: Sun Jul 09 2006, 01:18AM
Location: Germany/Hessen/Hanau
Posts: 9

Thanks again for all new hints ans suggestions!

It all comes down to buy more batteries (the sealed lead acid ones are quite nice). But these are ugly and heavy, too.

I can not simply use the 240V mains since the project will be an "outdoor" project where no mains power is available... only batteries are suitable.... :(

Greets,

Marcus

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