A better way to run with a dynamotor (unless you have a linear PS with at least 5X the running current rating of the DM) is to float a small lead acid battery across the power supply, set to around 27.5V.

A couple of garden tractor batteries in series, or a couple of 12V 7-10 AH gel cell will work well and are inexpensive.  Done this way, the dynamotor starts quickly, and the power supply keep the batteries topped.

A REGULATED float voltage of 27.5 volts will keep the batteries at full charge.  I have a 250 A switcher from which I run my 28V equipment, but it floats a large aircraft battery, which will start even my GRC-14, which has a DM as big

as a barn.  Dynamotor equipment performs much better if it is not current starved.  Voltage regulation, and hence stability is much better.

Scott W7SVJ

From: [email protected] <[email protected]> On Behalf Of Mark K3MSB
Sent: Friday, February 4, 2022 6:38 PM
To: ARC5 <[email protected]>
Subject: [ARC5] SCR-274N Dynamotor Question

I'm working on a new 28V power supply for my SCR-274N system as well as other projects.

I'm using a 28-0-28 V 50A Transformer with a bridge rectifier (so I'm not using the CT).   I'm using a 220V 16A Variac to set the primary voltage.

When the setting set for 28V key up,  I'm getting about a 4 to 5 volt drop key down.    

I didn't expect that much voltage drop as the transformer is pretty stout for an SCR-274N.

Can I run the system on 30 to 32V key up without damaging the dynamotor?  

This would be a short term fix as I suspect I'll need a VR circuit.

73 Mark K3MSB