[ARC5] Dynamotor Regulation

[WA5CAB at cs.com]

The "rule of thumb" for starting surge current expected from a medium size 
dynamotor is 3 to 5 times the rated full load amperes.  DM-33-A or 
DY-8/ARC-5 name plates (several seen over the years) don't actually give a rated FLA 
but instead give a primary (input) current at 28 VDC of 7A intermittent and 
5A continuous.  As the starting surge couldn't be expected to vary depending 
upon how you "planned" to use the machine, use the intermittent rating.  So 
expected starting surge is 21 to 35 A.

The reason that your typical say 24V/10A computer grade supply won't start 
a DM-33 is that they don't have any surge capability or actual current 
regulation but have a current limiter that folds back and shuts off the supply at 
something around 110 to 120% of their maximum continuous current rating.  

In a message dated 07/29/2017 07:40:27 AM Central Daylight Time, 
cliff52 at gmail.com writes: 
> please add to my last - I reread the original message and you did mention 
> the BC-456 so we're talking the dynamotor power supply for the modulator.  
> I hope someone updates my notes with what size batteries/ charger/ DC 
> Power Supply works with the larger dynamotor.  The server power supplies I 
> mentioned are available in quite large current ratings.73 - Cliff W4HGR
> 
> On Sat, Jul 29, 2017 at 8:19 AM, Cliff Miller <cliff52 at gmail.com> wrote:
> >> Have we clarified if we're talking about just a receiver or a 
>> receiver-transmitter system?  I have no experience with the dynamotor on the 
>> modulator for the transmitter so I can only speak to using the receiver 
>> dynamotors, which is smaller.I have successfully used 2-12V gel-cell batteries of 
>> 7A-h or more capacity, series-connected, to start the receiver dynamotors. 
>>  I've also used my 13.8V 25A ham power supply and a 12V gel-cell to run 
>> them / no problem.
>> 
>> 
>> The RC folks have pioneered the use of two 12V computer server power 
>> supplies, series-connected, to charge 24V model airplane batteries.  These are 
>> readily available in high current values since the server people just 
>> install new ones periodically because failure-is-not-an-option, etc.  The 
>> negative side is shorted to ground so you have to separate that on one of the 
>> supplies if you're going to connect them into 24V.  Lots of details on 
>> using these on some of the RC forums.
>> 
>> I bought two of these to experiment but have yet to try them.
>> 
>> Of course, eBay is your friend with various 24-28V high current power 
>> supplies available just about all the time.  I tried the server units since 
>> they're cheap (two for 15 bucks plus shipping).
>> 
>> 73 Cliff W4HGR
>>  
>> -- 
> Cliff Miller
> cliff52 at gmail.com
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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