[ARC5] 28 volt high-current supplies?

Sat Feb 26 13:08:42 EST 2022

I saw a spec on one that said max discharge was 300 amps for 5 seconds...

But, it's been brought to my attention, by a smarter engineer than me, 
that although the initial spike may be that large, as the motor starts 
turning, the current should drop substantially due to back EMF. I put 
new bearings in it so I know it's not "stuck", and it is turning at a 
pretty good clip... looking at the schematic shows a capacitor to ground 
on phase A (B is ground). Voltage there is very low too. Could be as 
simple as a short circuit! (crossing fingers).

As a former EE, I should have thought of that to begin with, but I don't 
have much experience with motor/generators or three-phase. Will post 
back with findings later!

On 2/26/22 11:57, arc5-request at mailman.qth.net wrote:
> Message: 1
> Date: Sat, 26 Feb 2022 12:57:03 -0500
> From: Bob kb8tq <kb8tq at n1k.org>
> To: Charles <charlesmorris800 at centurytel.net>
> Cc: ARC-5 <arc5 at mailman.qth.net>
> Subject: Re: [ARC5] 28 volt high-current supplies?
> Message-ID: <68B5A2A1-CA25-4BD1-9BE5-34299FC23541 at n1k.org>
> Content-Type: text/plain; charset="utf-8"
>
> Hi
>
> Small ( 22AH is small compared to 300A discharge) batteries of any sort are
> not going to help a lot (unless you have a lot of them ?). Something up around
> 300AH is what an SLA bank likely would need to get up to in order to do a good
> job.
>
> They aren?t cheap, but AGM?s could do the trick at a somewhat lower AH point.
> The aircraft likely had some huge batteries on it.
>
> Bob
>
>> On Feb 26, 2022, at 12:47 PM, Charles via ARC5 <arc5 at mailman.qth.net> wrote:
>>
>> I'm having a problem with the inrush (starting current)... several times the nameplate rating is not unusual for a DC motor.
>>
>> The DY-17A seems to be rated at 33 amps, so the inrush is probably on the order of 100 amps... my inverter, though, can draw up to 115 amps at full load. And indeed the inrush seems to be around 300 amps!! I don't know what kind of aircraft it came from, but it must have had a big generator and a good-sized battery in case of generator failure, too.
>>
>> Anyhow, a cobbled-up bench supply with a 20v 60 amp transformer (240 volt input), a 200-amp bridge, really heavy cables, and a BFC (large capacitor) can't get it up to full speed or maintain anywhere near 24 volts! :( It's noisy even at partial rpm. Would need to be in an insulated box or somewhere outside the room, or both...
>>
>> Parts aren't cheap like they used to be, especially in this category (might have more success at hamfests if there were any within a reasonable distance). By the time I get done building a super heavy duty 28 vdc, maybe I *should* just buy a PP-8474/G... but I can't find any specs on surge current capability. Any ideas? Even a schematic would help.
>>
>> It's starting to look like "battery-assist" is the way to go with a couple of 22 Ah or larger SLA batteries, and contactor-disconnecting them after start other than a trickle charge. The ripple current would be destructive to gel cells and I'm not sure a wet battery would take it well (plus I really don't want acid vapors in my shack...)
>>
>>
>>
>> On 2/17/22 20:39, Meir Ben-Dror WF2U wrote:
>>> I have 2 PP-8474G's. One is running my GRC-19 and the other replaced the original power supply (which has a problem I haven't addressed yet) in the GRC-142 shelter, for the GRC-106.
>>> I bought 2 24-28 VDC at 130 amps switching supplies - 240 vac input - on eBay some time ago ($60 each), that came out of a data center (probably for battery charging), which produce no RFI, so I use one for running the DY-17A for the ART-13, the other is a spare for now.
>>> I didn't notice that the 100 amp switcher on eBay I gave the link for, is cobbled up from 2 supplies...
>>>
>>> 73, Meir WF2U
>>> Landrum, SC
>>>
>>> Get BlueMail for Android <https://bluemail.me/>
>>> On Feb 17, 2022, at 8:47 PM, J Mcvey <ac2eu at yahoo.com <mailto:ac2eu at yahoo.com>> wrote:
>>> Raw SMPS are usually not suitable for radio power supplies. Espaecailly those cheap ones, which probably don't have any FCC compliance at all.
>>>
>>> There are some decent military SMPS radio supplies out there like PP-8474G or the GEI24-RPA-T.
>>> I have both . The latter is more modern and has better regulation . I had pigtail onnectors that are supposed to power radios in a rack, but I just use the charger output.
>>>
>>> On Thursday, February 17, 2022, 07:58:47 PM EST, Charles via ARC5 <arc5 at mailman.qth.net> <mailto:arc5 at mailman.qth.net> wrote:
>>>
>>>
>>> Thanks Meir, I saw that while searching... it's very obviously two 12 volt supplies wired in series without any diodes to avoid potential back-biasing during startup. Really professional job on the "24" sticker too (sarcasm).
>>>
>>> There's a perfect transformer if I decide to go linear, and the weight doesn't matter... but they just want too much!
>>>
>>> https://www.ebay.com/itm/165244216125 <https://www.ebay.com/itm/165244216125>
>>> -Charles
>>>
>>>
>>>
>>> On 2/17/22 18:54, Meir Ben-Dror WF2U wrote:
>>>
>>> This one should do it...
>>>
>>> https://www.ebay.com/itm/24-Volt-100-Amp-DC-Power-Supply-2400-watts-/164935380985?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=711-127632-2357-0 <https://www.ebay.com/itm/24-Volt-100-Amp-DC-Power-Supply-2400-watts-/164935380985?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=711-127632-2357-0>
>>>
>>> 73, Meir WF2U
>>> Landrum, SC
>>>
>>> Get BlueMail for Android <https://bluemail.me/>
>>> On Feb 17, 2022, at 6:54 PM, Charles via ARC5 < arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>> wrote:
>>> Looking for ideas on 24-28 volt supplies that won't break the bank.
>>> Shipping on big iron is REALLY expensive these days even if a suitably
>>> sized transformer can be found... Switching supplies from China aren't
>>> too bad. Two big batteries and a smaller charger to keep them up when
>>> not operating seems to be about the best compromise.
>>>
>>> I'd like to be able to make 100 amps DC (which needs a 240 volt outlet,
>>> of course).
>>>
>>> Any thoughts? thanks
>>>
>>> -Charles
>>>
>>> WB3JOK/0 since 1976
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