[ARC5] SCR274 field test

[Bill Cromwell]

Hi J,

You have answered the question about where your measurements were taken 
and the wire gauge to the dynamotors. You haven't said anything about 
the engine running or not. Try measuring the battery terminal voltage 
while you are cranking the engine. V-8 engines can drop that to 8 or 9 
volts! Those batteries have internal resistance that changes with the 
state of the charge (higher internal resistance when discharged).

Your cranking battery is designed for those high surge currents like 
starting the engine. But it won't tolerate being deeply discharged at 
all. How old, what condition, and what charge state was that battery? 
How do you know?

Deep cycle batteries have traded the high surge current capability for 
the 'deep discharge cycle' capability. They have a higher internal 
resistance (which gets higher as the battery discharges). You can expect 
a lower terminal voltage with a higher current draw, especially with 
high surge currents. What was the age, condition, and charge state of 
that battery when you tested it? How do you know?

The 'how do you know' questions have their answers in measurements of 
the specific gravity of the electrolyte and load tests to compare them 
to manufacturer's specifications. Sulphated and contaminated plates will 
reduce the energy available. So will *any* corrosion in the terminals 
(between the posts and connector).

Good luck with your project. I hope the solution to your problems is 
resolved by starting the engine.

73,

Bill



On 07/18/2015 08:28 PM, J Mcvey via ARC5 wrote:
> I was hoping that I could run the dual rx/tx setup off of my  jeep battery, but it seems it needs a stiffer deep cycle type to keep up with the load in transmit. The jeep batter sagged badly and for that matter so did the deep cycle battery (11v under full load), but it was sufficient to keep things working.
> I think i'm missing something about the nature of dynamotors and batteries ...
> With the two transmitter filaments ( 4X 1625) @ 2a and the rx pulling about 2.5a, that's a constant 4.5a, add the dyno in stanby which bring the the total cw break-in receive mode 7.5a.
> The dyno says 9a @ 12V continuous duty for 440v @ 200 ma .That should be a max of 16.5a a key down. So how can 16.5 amps draw a 130AH battery down to 11v from it's fully charged resting voltage of 12.6v ? ( it recovers on key up)
> When I was using a SMPS, it sounded good, now I've got some chirp due to power droop.What say you experts?
> BTW, I was doing this in "original spec" using a very short wire antenna of about 35 feet on 80 meters in NVIS config. Loads right up at about 50% inductance with coupling also about 50%. I like to stick a NE-2 ( leads shorted together) in the antenna clip on the bc-442 to see how bright I can make it glow. It tracks well with antenna current.
>