Regulating a 48V bank to 24V

[feeench]

I'm trying to come up with a plan to power a Quickie and Quicksand combination for extended periods of time without changing batteries.

If I have a bank of 4 12V SLA batteries what would be the best way to knock 48V down to 24V (instead of the stock 18V)? Is there any disadvantage in using SLA's and/or regulating power sonically?

I was thinking of using a separate battery to power the heater filaments in the Quickie, thoughts? Regulating 48V to 1.5V sounds like a lot of work...

[Grainger49]

Two 12V SLA batteries in series yields 24V.  Series the other two and put them in parallel you have double the amp hour rating.

I'm no help on the heater voltage.  But trying to whittle even 12V down to 1.5 is going to be wasteful.

[mcandmar]

12v to 1.5v is a tricky one.  With a basic LM317 voltage regulator its going to get warm dissipating that much voltage, it is doable with such a low current draw but its not ideal. There is probably a very simple and clever way to drop the voltage that i'm just not seeing, or you could chain a few regulators in series, use one to drop to say 9v or 5v, then another for the final 1.4v. From memory in my AC quickie the regulators are fed 6-7v DC and they stay cool.

[feeench]

Two 12V SLA batteries in series yields 24V.  Series the other two and put them in parallel you have double the amp hour rating.

I'm no help on the heater voltage.  But trying to whittle even 12V down to 1.5 is going to be wasteful.

I should be more clear. I want a 48V and a 24V tap from my battery bank. I was hoping to get away with 4 batteries for this but maybe I should just grab 6 batteries and set 4 up in series for 48V and the other two for my 24V.

As for the 1.5V there are many 6V (and some 3.6V perhaps) batteries that could be regulated down to make work. My knowledge is quite limited in this area but I think it might be possible to use resistors for this application.

[Grainger49]

Four 12V SLAs all in series gives your 48V supply.  You can tap off at half way and there will be a slightly higher drain on those two batteries.  But my experience with SLA batteries is that you charge more often than drain them. 

The 48V string can be shared by both channels.  I'm not sure about the 12V tap.  Keep in mind that the heaters must be independent for each channel of the Quickie.

I have no information on the Quicksand.

[feeench]

But my experience with SLA batteries is that you charge more often than drain them.

Really? I would expect them to last quite a while before having to recharge them.

Also, I can't believe I didn't realize I could just tap off at half way. I'm always trying to figure out the most advanced way to do things. I gotta get back to basics!

[Grainger49]

I agree, but my Ack! dAck! is on charge (off position charges) more often than it is on.

[Paul Joppa]

Here is a wikipedia article; check the column for self-discharge, 3-4% per month for lead-acid for example. Unfortunately most lead-acid batteries will suffer damage if they are not recharged quickly after use.

Efficient regulators for large voltage ratios do exist, but they are digital pulse-width modulators and generate the kind of noise that we are using batteries to avoid. If you are willing to go that route you might as well generate the high voltage from a low voltage battery, using the same technology, and run everything off a single battery.

Quickie should work acceptably with a high voltage of 24 volts, so it can share a 24v power supply with Quicksand.

I still think alkalines are the most reliable power for the filaments due to their very low self-discharge rate. For longevity, you can parallel  any number of them.

Low-self-discharge NiMH (sometimes called "pre-charged") have the advantage of a fairly constant voltage. It's not easy to find them in D-cell size - look for 8000-10000 mA-hours - and they hold their charge about as well as lead-acid without the tendency to sulphate. I don't know how well they deal with being paralleled.

[feeench]

Oops. I just realized the Quickie was meant for 36V not 48V... Not sure how I arrived at 48V...

Perhaps a bank of 5 batteries @ 6V could power both, I understand that's the max for the Tripath chip.

I think I may just go with the stock setup and stick to rechargeable batteries... Do different battery chemistries have much of an effect on the sound?

EDIT: Maybe I've flubbed again. Is the quickie 18V per tube? or 36V?

[Paul Birkeland]

The Quickie needs two separate 1.5V batteries, and one bank of 36V.

[Paul Joppa]

To be accurate, Quickie was designed to operate from alkaline batteries, which drop in voltage as they discharge. For that reason, the design range is 24 to 36 volts with filament cells of 1.0 to 1.5 volts. The center of that design range is of 30 volts and 1.25 volts.

That said, the high voltage supply can go as high as 72 volts with no other real changes; more voltage gives greater maximum output voltage.

[Natural Sound]

I've been running my Quickie at 42 volts for 4 years now and never had any problems. I only have to charge the batteries 4 or 5 times per year too.

http://bottlehead.com/smf/index.php?topic=1242.0