Regulating voltage?

[Singularity35]

I hope this is the right place to post this thread. If not, I apologize and please move to appropriate area mods.

Here's my quandary and I'm hoping to get some suggestions.

My Yaesu FT-857D runs hot even on standby mode on the 13.8vdc that my PSU supplies. I read that all my radio needs is 10vdc to put out full power(something with the exciter stage). So I lowered the output voltage on my PSU to 12vdc(which solved the heat problem). Now the problem is that voltage drops to below 10vdc(to around 9.2) when I transmit on full power and audio starts to break up.

Here's what I thought up but I don't know if it's feasible. I up the output on my PSU to 13.8 and I put some kind of voltage regulator on my power line to get only 10 or 11 volts.

My question is, will this work? And how do I do it? Thanks in advance folks.

 

[Robb]

Why does your 857 run so hot? The power amp section should only get hot if you are transmitting. If it doesn't have a fan kit on it or the fan doesn't have enough flow, I would fix that first.

13.8v is what you should run.

If your voltage drops that low when transmitting; then it is a fair bet that your power supply is too small for your application. Need a bigger better supply with a higher amperage rating,

Adding another regulator?!?
NOT!

 

[Singularity35]

Why does your 857 run so hot? The power amp section should only get hot if you are transmitting. If it doesn't have a fan kit on it or the fan doesn't have enough flow, I would fix that first.

13.8v is what you should run.

If your voltage drops that low when transmitting; then it is a fair bet that your power supply is too small for your application. Need a bigger better supply with a higher amperage rating,

Adding another regulator?!?
NOT!

Thanks for the answer.

Temperature in the shade is pretty high in the Philippines. I have the running hot trouble only during the afternoons where temp gets to around 32-35°C. The supply I'm using is a 30 amp one that has no trouble driving my Mirage B-3016.

Maybe I should just try running it at 13vdc? And maybe get a bigger blower? I do have the 4 inch square blowers on my 2 meter units and on the FT-857.

 

[wavrider]

Exactly, I just got back from vacation in Philippines, if you do not have Air conditioning it is HOT, I mean REAL HOT.

SO I would not use the hf rig during the heat of the day, and I would also try to find a small fan and put on the rig when I do use it.

The voltage is not the issue, it is the heat.

 

[Singularity35]

Exactly, I just got back from vacation in Philippines, if you do not have Air conditioning it is HOT, I mean REAL HOT.

SO I would not use the hf rig during the heat of the day, and I would also try to find a small fan and put on the rig when I do use it.

The voltage is not the issue, it is the heat.

Yes, with AC, I didn't have a problem.

Thanks. I just upped the PSU to 13vdc and bought a small fan. Seems to do ok.

I just read this during some researching so I thought I'd reduce PSU output.

 

[222DBFL]

Get the voltage back up to around 13.8vdc. Use a good brushless fan that will move some air and install it. Turn the power down as much as possible and keep the QSO's short. Heat is electrical components enemy!!! They don't play well together. That or water in most cases!! Keep cool down there. If Wavrider says it's HOT! Down there than I'm sure it is, as I know it's not cool during the summer where he lives either!!

 

[Singularity35]

Get the voltage back up to around 13.8vdc. Use a good brushless fan that will move some air and install it. Turn the power down as much as possible and keep the QSO's short. Heat is electrical components enemy!!! They don't play well together. That or water in most cases!! Keep cool down there. If Wavrider says it's HOT! Down there than I'm sure it is, as I know it's not cool during the summer where he lives either!!

Thanks. I have it up now to 13vdc and I just bought a small fan.I tested it out with a long ragchew on full power this afternoon just to see how hot it got. With the small fan and no AC on, it actually just got a little warm. Voltage didn't drop below 11vdc but it also probably helped that I tightened the connections from the PSU's terminals to the binding posts that I modded the PSU with.

So I should just ignore that article about the 2SK2975's needing just 10vdc?

 

[222DBFL]

Try it. What does the manual state as the proper voltage and amperage needed?? Guess you could run the voltage back down to 12vdc or there about and with volt meter on PSU, see if voltage sustains or drops. If it holds and rf power is at or near full output, it may be best to run it that way. But I would read the manula first and go off of it. I think the manufacturer knows what Voltage and amperage are needed!! JMHO.

 

[222DBFL]

With a true 30 amp supply and that radio that is what 100 watts? It should not drop voltage much if at all if the amps are true 100% duty cycle rated. Now if they aren't then a better PSU may be needed.

 

[RatsoW8]

I owned an 857D and still have a pdf copy if the manual. Yaesu calls for 13.8 volts +-15% to power the radio and a 22A current pull for full power, Why would you run it at 10 volts and expect it to work? I would run it on a solid 30 amp supply at 13.8 volts.

Add a cooling fan if you have to but I think your asking for trouble down the road running the rig at a minimum voltage.

 

[Captain Kilowatt]

Forget the 10 volt business. The 817 was designed as a qrp rig to run off batteries. The finals may like 10 volts and everything else may work well at 10 volts however the 857 is not designed for qrp and will not tolerate low voltages. I have an 857 and it runs great on 13.8 volts but dies at 11.0 or so.

 

[Singularity35]

Thanks, guys. I really appreciate having a bunch of knowledgeable guys on tap. I am basically going at this on my own where I am. Most guys here set up their station with the help of their Elmers who basically check out the station personally. I have no such luxury.

Once again, much thanks. Cap and the group.