[ARC5] 24vdc power

Mon Sep 5 13:00:39 EDT 2022

In may shack, I have been using the same four 200 AH 6V golf cart batteries for the past 11 years.  They were used when I got them.  The live in a very controlled environment, and they are floated at the 

Ideal voltage for the ambient temperature.  I check the water every year or so, adding distilled water if needed.  The unit will spin up any boatanchor I throw at it- GRC-19, GRC-14, TRC-75, BC-375.

It is like have a real aircraft bus or vehicle bus at one’s disposal, the dynamotors spin up very quickly, and the voltage droop at startup is less than a volt.  For my money, there is not better, low stress, maximum performance way

To run dynamotor or rotary inverter loads.  Some folks don’t like the idea of large flooded batteries indoors, but good maintenance mitigates the risk of gassing or leakage.  A good fat linear is great, and I have built and used them by the 

Scores, and in fact would be willing to unload many large 28V power supplies and GPU’s if someone needs one and would be willing to pick it up in Arizona.  I just feel that the floated battery approach gives the ultimate level of performance for the least

Amount of hassle.  (By the way, I had an avionics shop years ago, and used a 400A regulated Christie GPU to power the benches, I still floated a 24V Gill 50AH battery across the line to reduce ripple and noise).

Scott

From: Charles <charlesmorris800 at centurytel.net> 
Sent: Sunday, September 4, 2022 11:15 PM
To: scottjohnson1 at cox.net; arc5 at mailman.qth.net
Subject: Re: [ARC5] 24vdc power

For the small loads mentioned here, that approach is a good one, although I have read that battery life may be limited. Unfortunately for larger SLA or flooded batteries, and switchers too, the price increases more than proportionately ;) 

It was actually cheaper for me to buy some of the components for the brute force PS than to buy batteries (and switchers).

On 9/4/22 23:06, scottjohnson1 at cox.net <mailto:scottjohnson1 at cox.net>  wrote:

I wish I saved my old posts on this subject since it comes up every so
often!  I find the best way to operate rotating machinery that once operated
in a mobile environment is to replicate that environment.  SO-
Get a power supply that can handle the full load current and float an SLA
battery across it.  Size of the battery and power supply is proportional to
load, but in your case, a 10-20 A switcher. Set to27.5 V (for normal indoor
ambient temperature)
Less for hotter, more for cooler, but in the range of 27-28V.  For your 10A
load, 12V 7AH SLA batteries would do nicely. (Two in series).  Increase AH
capacity proportionately for higher current loads.  Amazon and eBay have
plenty of inexpensive switcher that will work, just don't buy the REALLY
cheap ones, unless you like the acrid smell of burning components.

-----Original Message-----
From: arc5-bounces at mailman.qth.net <mailto:arc5-bounces at mailman.qth.net>   <mailto:arc5-bounces at mailman.qth.net> <arc5-bounces at mailman.qth.net> On Behalf
Of Charles via ARC5
Sent: Sunday, September 4, 2022 10:23 AM
To: arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net> 
Subject: Re: [ARC5] 24vdc power

Hey guys,
What's everybody using to provide 24vdc for your military radios? Two

12vdc supplies in series?  Home brew?  Do they make a 24vdc switching supply
that will handle 10 amps or so?

Thanks for your input,

Richard kn7sfz

Anything with a dynamotor needs about five times the motor nameplate current
for the starting surge...

I got a 2 KVA three-phase 115V 400 Hz rotary converter at a flea market but
nothing I had was big enough to start it (rated at 27.5VDC at 115 amps!)

So I bought a 20 VAC, 5 KVA toroid transformer on ebay, a BFBR (big bridge
rectifier), heat sink, a 220,000 uF cap, meters and shunts, and brewed up a
24-28V 120 amp brute force supply with 240 VAC input. THAT starts the
converter all right. It doesn't even blink at smaller dynamotors :)

-Charles, WB3JOK/0

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