[TowerTalk] FW: [tdxs-list] HLA300 linear amp

Matt maflukey at gmail.com
Wed Apr 16 00:20:21 EDT 2014

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!








From: Steve Smothers [mailto:cougar70 at 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 - 


.-----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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