Rekindling my radio interest

Thanks Matt, that’s encouraging. I was thinking of using 40-50W keeping a little in hand if needed for that pesky QSO.
I take it watching the voltage on these isn’t much of an option to monitor drain, as they hold up well to the end don’t they?

Just a little word of concern, a fully charged 4S LifePo will deliver up to 16.8 volts albeit for a relatively short period. I would have thought that was outside the spec for the 897, there’s an article somewhere about using high power diodes to drop the voltage initially then auto switching them out of circuit when the voltage drops to a suitable level. If I can find it i’ll post a link.

73

Victor GI4ONL

i had the same problem with the UK warehouse so I got the UK based Accell6 and the Hobbyking 105W power supply.
Very good!

Tasos

Hi Victor, all

Need to be careful to distinguish between Lithium Polymer (LiPo) and Lithium-Iron Phosphate (LiFePO4) chemistries.

Fully charged voltage for a LiPo cell is 4.2V so 4S would be 16.8V. However for a LiFePO4 cell the maximum voltage is only around 3.6, giving 14.4V for a 4S battery which is OK for nominally 13.8V radios. The plateau voltage for LiFePO4 cells is 3.2 so for most of the battery’s usable discharge period voltage is around 12.8, which is fine for the FT857/897 (and many others) :smile:

73 de Paul G4MD

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Oops thanks Paul :flushed:

small panic moment over for me there!! :smile:

No prob Victor :smile:

You’re quite right about using a string of high powered diodes to “tame” a 4S LiPo to run a 13.8V radio - it was the standard technique before LiFePO4 became readily available. (The idea was, placed in series with the supply, forward biased they provided a voltage drop of around 0.6V per diode, you just shorted them out as the terminal voltage of the battery dropped as it discharged). Never saw an auto version though, that would be less fraught with danger…

Never tried it myself - my trusty 817’s are very happy on 3S LiPo’s and I’m not about to cart my FT101 up a hill :wink:

73 de Paul G4MD

Phil AD5X published one in QST this year. It used a relay to bypass a pair of power diodes. The default state was power diodes in circuit but when the voltage dropped the voltage switch powered the relay and shorted the diodes. The result was it failed safe by putting the dropping diodes in circuit. Nice and cute idea.

Then you waste ~200mA powering the coil continuously, latching relay would be the best, unless you favored dropping the voltage down first with a DPST relay Still working on my converter.

Jonathan.

Next best thing to a latching relay would be to use a ‘normally closed’ contact pair to short out a resistor in series with the coil. The ‘hold’ current is a lot less than the ‘operate’ current, depending on the spring loading etc. Select resistor value for the particular relay.
In this application there should never be more than a volt or so across the main contacts, so you could slacken off the spring load quite a lot too, as it is mainly to open the contacts quickly to minimise arcing. That would minimise the hold current…

Adrian
G4AZS

Many ways to do it, A D-type FF could also be used with a buffer.

Problem I have often found with relays is that they change with temperature. I have found this with soft-start circuits using series coil resistors, though I suppose in this application the point of switching is not important.

Its an interesting idea. It has got me thinking, I still have two 1N5401’s in series on my pack.

Jonathan

Here are AD5X’s non-automatic voltage reducers. They are in-line with power poles. One even has an LED!

http://www.ad5x.com/images/Articles/Vreducer.pdf
http://www.ad5x.com/images/Articles/LiPo%20Battery%20Reducer.pdf

wunder

Looks like Phil’s webserver has been slashdotted by the SOTA crowd :wink:

After Phil’s webserver gave up in disgust, I looked through my QSTs (I get the online only subscription and print the whole issue to PDF for use on the tablet).

One he does the circuit the other way around, the relay is powered when the volts are high and that puts the diodes in circuit. So if the voltage detector/relay failed it could put all 16.8V on the output. And secondly, he isn’t using the relay out of Ferrybridge Power Station that switches all 2GW output but something smaller. So the operating current is 26mA not 200mA!

Now I admit to getting grumpier, senile and confused as I age so it must have been me that thought, “oh no swap the logic so it fails safe” and not Phil and I’ve thought it such a spiffingly top notch idea I’ve subconsciously donated it back to Phil.

Anyway, QST April 2015 page 39.

I was thinking along the lines of an automotive relay coil R = 80-90 Ohms. You would get those currents with a PCB relay though - be a real nuisance to solder, but yes it would work better.

Indeed, a PCB relay is what is used. here’s the completed unit ( © ARRL).

I’m not posting the circuit, buy the magazine if you want to see what it is!

Very neat ! Homebrew PCB as well gets my vote…

Ah, I knew I had seen it somewhere recently :grinning:

Victor GI4ONL

Hi Peter,
I’ve been trawling all the yagi design sites for some time now, and have decided I think my best bet is one of the DK7ZB designs like you have used.
I’m taking it you built Type 1 from that page, with the nicest SWR plot?
Did you apply a boom correction on the elements, and if so, what sums did you use?
How are you retaining the directors and reflector? (I can’t really tell from your page)
Looks like you have drilled the driven element sections? I remember flattening and drilling a 4mm hole in 4mm elements for my DJ9BV contest yagis. That was ‘fun’ :smile:
Did you model for the offset driven?

I use my Kenwood ts480 for sota as its my only HF rig and its 4kg. I have swapped a 12 ah slab battery for a 4200mah lifepo4 battery from hobbyking. Its only 500g in weight compared to 2 or 3kg of the slab.