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Old 13th August 2009, 03:51 PM   #1
Brit01 is offline Brit01  United Kingdom
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Default Sealed Lead Acid Batteries

Hi guys,

Just to raise a question on this topic again.

I want to use a 6V SLA to supply heaters on the demanding 6080's.

Well just one tube at 2.5 Amps.

I'm planning to buy a 4 Amp SLA.

Now coming to charging this thing.

I understand I can charge it slowly when the amp is switched off at 1.1 times the rated voltage.

I have a small power supply rated at 7.5 volts (other voltage selections available) at 500mA.

Will this be suitable to charge it?
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Old 13th August 2009, 03:56 PM   #2
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Default Re: Sealed Lead Acid Batteries

Quote:
Originally posted by Brit01
Well just one tube at 2.5 Amps.

I'm planning to buy a 4 Amp SLA.
Do you mean a 4 Amp-hours SLA? As in 1 hour 36 minutes worth of 2.5 Amps? Forget this plan?
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Old 13th August 2009, 04:05 PM   #3
Brit01 is offline Brit01  United Kingdom
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What about a 10amp SLA? Just 4 hours then

I need to check if this is the AH or not. Details on the web do not state this.
Or a new piece of iron then.

update: Yep it's a/h.
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Old 13th August 2009, 06:14 PM   #4
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I recommend you look at the real life implications of this scheme.

Find a discharge curve for a real SLA battery and look at the voltage
drop over time at the current you plan to run.

I think you will be looking at a C/10 discharge (2.5 amps from a 25 AH
battery) or less, and still may not like the resulting voltage curve.

To fully charge SLA batteries requires at least a 2 stage charger where
the final charge is at a lower rate than the bulk charge. This is needed
to fully charge the battery in any reasonable time.

Then, you may only discharge SLA batteries down to about 50% of
their AH capacity on a regular basis. Deeper discharge will shorten
the lifetime. At 50% under discharge, the voltage will be quite a bit
lower than at full charge.

Is it worth it?

Michael
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Old 13th August 2009, 06:28 PM   #5
Brit01 is offline Brit01  United Kingdom
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Very valid point and good explanation.

After you explain it like that then better to go for a piece of iron for the 6080's.

Cheers
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Old 13th August 2009, 08:34 PM   #6
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Default I'd still be inclined to give it a go

SERIES connect hte heaters so you are running at 12V. THat halves your current requirement immediately and gets you a better discharge curve to boot.

Yeah, two stage charging would be great, but hte reality is your amp will spend maybe 4 hours on, then 4 days off. A slow flat charge curve is entirely reasonable in this setting.

Cost and speed to impliment would be significantly less than getting the "right" transformer, and you have the holy grail - no heater hum.
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Old 13th August 2009, 08:37 PM   #7
infinia is offline infinia  United States
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Guidelines for lead acid batteries are never to, or rarely discharge past 50% of its AH capacity. Also being it's not too practical to get past charging up to or over 90% of the AH capacity (time, eff & heating factors). So what you have to work with, on a repeat charge/discharge cycling basis, is only around 40% of a batteries AH capacity ie if you want to live up to a reasonable life expectancy of the battery.
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Old 13th August 2009, 09:05 PM   #8
Brit01 is offline Brit01  United Kingdom
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Quote:
SERIES connect hte heaters so you are running at 12V. THat halves your current requirement immediately and gets you a better discharge curve to boot.
I was planning to use only one 6080 for a headphone amp. Yes series would have been possible with 2 tubes but not in this case unfortunately.
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Old 14th August 2009, 01:44 AM   #9
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These batteries also loose their capacity to take a charge pretty quickly...Service life might be less than 6 mos.
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Old 14th August 2009, 02:36 AM   #10
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Default kinda depends...

"those batteries" is a pretty broad ranging qualification. Batteries built for fire alarm or security system use are pretty damn reliable in my experience. One has been running my mountainbike lighting (50W @ 12v) for six years now including numerous complete discharges, several epic crashes, and a low tech charging system (panasonic cordless phone wall wart).

Hell, I've talked myself into it - I'm going to battery heat the PC900's in my phono pre and get back to you on the performance!

Cheers
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