I am looking for 2 X EverReady Type 482 45v HT battery and 2 X EverReady Type 745 1.5v LT battery, (To suit HMV B61B portable radio)

Other make equivalents are OK as well.

Please email me with what you have with price and postage to 2810 NSW.

T I A

Clive, I make up HT battery packs, in this case using 30 x AA alkaline cells for each 45 volt battery.
For the A battery, 6 or 8 D alkaline cells in parallel using a modified battery holder.

Jaycar has battery holders that are suitable.

Aldi currently has AA alkaline packs of 50 - they are cheap and good.

I used to run my Technico portable radio on a set of these, for about 1 hour each morning. I got about 2 years from a set of batteries, alkalines last about 10x longer than carbon-zinc cells. But beware, the voltage and current from an AA alkaline pack can be lethal.

Were you looking for original batteries to put the new cells in? You won't get any working ones!

I might have scans of the battery cases on my old desktop - haven't fired it up in some years but I'll do so if you plan to make replicas.

Another way to get 45 volts is to join up 5x 9volt batteries, they even clip together for convenience.

Thanks guys , but I have never liked using large numbers of batteries and I will probably go with the electronic battery which only requires 6-9 volts.
Yes Ian I will be looking to make them look like the original battery, so any scans would be great.

Clive

https://www.youtube.com/watch?v=8hwLHdBTQ7s

Going that high with batteries of that kind is asking for trouble. DC punctures healthy, normal skin at roughly 110V. The danger is that if the negative crocodile clip came into contact with the case of the battery it was connected to it could have provided the metal cases of the battery pack with a path of least resistance which would have come into contact with the clip on the positive lead. When breaking contact with the positive terminal the spark would have jumped to his hand killing him instantly.

The nominal resistance of healthy skin is around 600Ω. 2200V ÷ 600Ω = 3.7A. Even though that battery pack wouldn't have delivered that current, it would have delivered more than the 50mA required to stop his heart beating.

The reason the condenser didn't blow was probably again due to the very low current flow. Type 216s don't have a lot of puff in them.

Yet another promising candidate for a Darwin Award.

Yes GTC I agree! Only problem is, he survived!

I assume he must work somewhere where they use radio mics and (wisely) replace the 216s after each use.

Alkalines can deliver respectable current. Some years back, when I needed to drill some 25mm holes in some concrete and didn't have a long enough extension lead, I used 2 sets of radio batteries totalling 180v DC to power my Hilti hammer drill. No problem!

But Clive, the issue with DC - DC converters is noise. If you need your radio to pick up weak signals (like ABC Newsradio 630kHz on Sydney's northern beaches) you cannot have a DC - DC converter running in the house, let alone inside your radio. I had to replace all the halogen downlight converters in my place with old-style iron and copper transformers. Even if you enclose your converter in a metal box with ferrites and feedthrough caps it'll still get out. I know, I design these things and I have to get them through EMC/EMI testing for CE certification.

The alternative is to run your converter at a very low frequency and round off all the edges. But doing this you take a big efficiency hit. If you want to actually USE your radio on a daily basis the low-tech AA's are still the way to go IMHO.

To make your 45 volt battery built out of AA's intrinsically safe, you could fit a polyfuse in series, inside the pack. Element14 (au.element14.com) part number 1707582 is a 60 volt 100mA PTC. These devices behave like a S/C when carrying under the rated current but go O/C when you reach, in this case, 200mA. The nice thing is they reset themselves. We used them for many years to protect our products from ham-fisted installers, we use a similar SMD part now.

For the 45 volt batteries I use 3 x Jaycar part number PH9210 battery holders . For the A battery I use 8 x PH9218 connected in parallel.
For my little AWA personal portable which needs a 67.5v B battery I use 8 x alkaline 216s clipped together as suggested by Robbbert - that gives 72 volts and fits in the original battery bay nicely.

Hope this helps. I'll fire up the old desktop at home on the weekend and see if I can find those battery box scans.

Thanks Ian, good info. The unit I was looking at using was from HRSA member Tony Maher. He sent me the complete article to read and it seemed to be a good setup.
I am not into circuit design and have no experience with dc-dc converters.

I was interested in the unit as one of the radios is for my son in law who is not electrically minded and it would make for simpler battery replacement.
Have you seen or heard of these units?

Clive

Hi Clive

I have built 2 of the early versions of Tony's Inverters. I cant find issue with them if built correctly. The start Stop feature is handy. I use mine regularly to power one of my old STC Batt Portables. I do not get any Hash that I can notice with that radio. I was still able when in ACT pick up all stations that I could on a normal Mains Powered set with the same antenna setup (Random wire antenna out the window of the garage)

Link to the radio I use it in: http://www.radiomuseum.org/r/stcaus_510.html

Thanks for that report Flakes, I wonder if it because you radio has an RF amplifier up front and that sets that don't struggle with faint signals.

I don't know what frequency the converter runs at so it could be way out of the Broadcast band.

Hi Clive, Flakes

I use my portables as they are intended, i.e. as portables with internal loop antenna. Therein lies the problem, the proximity of the converter to the antenna.

DC - DC converters use square waves. A perfect square wave has harmonics out to infinity. So even if the fundamental switching frequency is in the order of 20kHz, the harmonics from a typical design extend to the 10s of megahertz. An external antenna will pick up a stronger signal at a distance from the converter noise source. But in my case that doesn't help because a horrendous noise source centred on about 650kHz pervades the entire area for 100 metres or so and you need the directional characteristics of the loop antenna to rotate the radio and null it out. ABC 702, with its 50 kilowatt transmitter at Homebush Bay, has enough grunt to punch through it, 630, using RN's standby transmitter and a directional array with a north-south null, has a lot of trouble penetrating the background noise on the 'beaches.

A pack of AA alkalines as suggested will last for years with typical use and can be refreshed with new cells in about 10 - 15 minutes.

Hi Ian

I will give it a work out tonight with just using the internal Loop Antenna in the back cover of the radio. I never liked how directional it was, seemed it needed to point the opposite direction to where I was .

I will test the inverter against bench top supply using conventional Transformer and diode bridge and see if I can pick up by a tuned ear what the difference is. I may be able to get the supply into the bottom of the STC, Think that's what I built it for but it was a few years ago.

From memory, Tony's converter uses Fets switched at 50Hz into a Reversed 12v / 240v transformer. After that it is rectified and smothered etc. So basically a solid state Vibrator PS... It would be interesting to look at the O/P of it and see what the harmonics are doing.

I have a few other Valve Portables as well, but the STC is my favourite because of the tone it gives from being baffled properly. I Will give them a run as well just to see how they perform.

I must say that I am not a fan of putting that many AA's in series for the reason shown above. I Posted it as a joke but there is a problem with the breakdown voltage of small cells. they aren't designed to withstand the punishment of 60 of them in series (to give 90 ish volts). The risk of one of them punching through at that voltage is very High. Take a look at the small "Gap" between where the positive terminal is and the case of the battery, It will have a very thin piece of a rubber like insulation and that's all.

Yes, that's called a Royer converter. Running at 50 or 100 Hz into an iron cored transformer with the secondary winding tuned, you'll get something approaching a sine wave with few significant harmonics. Efficiency is not great though.

Look out for magnetic field from the transformer. If you pick up buzz with it installed inside your radio, a copper field shorting strap around the transformer (assuming it's an E - I lamination type like a speaker transformer) should help.