I ran a 1.2kW homebrew SS amp in my mobile for about 10 years using pairs of
group 24 automotive batteries connected in parallel. The following
calculations proved out more-or-less correct though some measurements that I
made:
Peak input power = output / efficiency = ~1200/.6 = ~2000w peak
For compressed SSB, average input power = input power x duty cycle = ~2000 x
.40 = 800w average
Automotive batteries are typically rated 60-120 amp hrs. The average total
stored energy is about 1,000 watt-hrs per battery BUT voltage will fall off as
a function of charge level and discharge current rate. A point is reached
where amplifier output will become non-linear well before the battery is fully
discharged. Therefore, the full storage capacity of the battery(s) is not be
realistically usable. Full discharge cycling of a lead acid batteries also
significantly shortens the life of the battery anyway.
Back to the math… at 30-40 amp average discharge rate, typical battery
voltage will fall off according to state-of-charge as follows:
100% charge – 11.7v
70% charge – 11.5v
40% charge – 11.0v
30% charge – 10.7v
20% charge – 10.3v
10% charge - <10v
Remember that these are voltages under 30-40 amps average load – not while
idling.
Considering that the amp pulled about 160A of current on voice peaks, I would
typically only run the batteries down to around 40% (11v nominal during
transmit) before recharging. This would give me about an hour of useable
transmit time as follows:
2 x 1000W-hrs x 40% / 800W = ~60 minutes of transmit time.
If you are looking at using a 300w output amp with a single auto battery, then
you should see about 2hrs of useable transmit time per charge.
P.S. When looking for batteries – go for the largest case size per
cold-crank-amp rating. My experience is that they will generally give you the
longest service life. I have found that group 27’s are the best if you can
find them at a reasonable cost, group 24’s are typically the best in $ per
service life. Avoid the newer small case batteries. I have personally found
that “deep cycle” batteries were not worth the premium cost….
Hope this is info is useful to you & have fun!
73
Matt
KM5VI
From: Steve Smothers [mailto:cougar70@earthlink.net]
Sent: Saturday, April 12, 2014 6:53 PM
To: James Carmody; tdxs-list
Subject: Re: [tdxs-list] HLA300 linear amp
Spec says you'll need a supply of at least 40 amps at 12-14v DC. I would
think almost any auto battery would be capable of that, but for how long is the
question. When I put a new one on for the US Islands Awards program, I used a
regular deep cycle marine battery and operated my 100w rig for a few hours
with no problem.
Steve -
W9DX
.-----Original Message-----
From: James Carmody
Sent: Apr 12, 2014 6:43 PM
To: tdxs-list
Subject: [tdxs-list] HLA300 linear amp
Anybody have one? I just got one very cheap on eBay but have not fired it up
yet. Debating on whether to power it with a small auto battery (higher current
than deep cycle) trickle charged. Tuner?
Jim NN5O
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