I think the Trojans are about 120 ah. So they in theory would supply 80
amps for 90 minutes continuous. Longer loaded time if loaded
intermittantly. But they survive much longer if less than half that
capacity is used before recharging.
SSB duty cycle depends the microphone, the transmit filter, the user's
voice, the radio's ALC, and any speech processing. The deeper into ALC
and the more the speech processing the greater the duty cycle while
transmitting. And if on a net with 8 participants the duty cycle is cut
to a quarter of two stations talking back and forth. If working a
contest and making 120 contacts an hour the SSB or CW duty cycle is
fairly high, but not over 50% because you do have to listen too. CW in
QSO or contest is probably about 25% duty cycle in rag chew or contest
because of about equal listening times.
100 watts out probably takes 200 DC. The Herc II runs 1 KW in so 5 times
the power.
And then you need enough charger or power supply to keep up with the
total energy use. With a transceiver you still draw several amps receive
with 20 or 22 transmit for 100 watts.
By watching the terminal voltage (fortunately the terminal voltage on a
lead acid battery is a good indicator of charge condition), if it goes
steadily down during an operating period, the charger isn't enough. If
it holds steady near 13.8 for a deep cycle battery, then the charger is
big enough, if it holds steady near 13.8 while transmitting, then the
charger is doing most of the work. Or if the charger ammeter stays at
full current rating for hours after an operating session, it wasn't
quite big enough. If it stays there for a week (like a battery tender
might), it was sure not big enough.
73, Jerry, K0CQ
On 2/5/2011 4:20 PM, NL7VL wrote:
According to the Herc II manual it draws 80 to 100 amps for 1 KW input.
Batteries last even better if the discharge is less than 50%.
Absolutely! I know that with CW you are actually looking at a 50% duty
cycle but I'm not sure about SSB. A pair of 6 volt batteries will
handle several hours of SSB at 100 watts, but we are talking about a
quality battery like a Trojan. An RV size 27 will be well on its way to
total discharge after a couple of hours at 20 amps after a few times
at a heavy discharge rate. The next size up will double the capacity
still giving you 2 hours at 20+ amps, but you've only discharged them
50% or a bit less. Your batteries will now live through 200+ charge
cycles or 4-5 years.
With the RV batteries you are looking at about $100 x 2, but the
Trojans will run at least $300 for the pair. Dang expensive! But that's
what you have to do to protect you investment.
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