Solar Powered Amplifier?

[Joe Hart]

I have been doing some Google research (and searched DIYStompboxes) and have only found some basic info (and some just incorrect specific info -- wrong pin numbers on schematics, etc...), but a friend of mine asked about a solar powered amplifier.  She sings and plays acoustic guitar for kids and usually uses a simple amp to boost vocals and guitar, but she would like to be able to free herself from the tyrany of the electric outlet and sing out in the freash air.

I was thinking that a couple of solar panels that could produce 18V and 400mA (but more panels could increase that) powering about a 10W amp (is that even possible??) with a battery backup (with solar charger, of course) would be perfect.  Now the issue, I've built some pedals, modded some solid state amps, and wired many a guitar, but I really don't know tons about electrical theory and such (I am NOT afraid to do my own footwork on some stuff, though).  I just don't really know how to proceed from here.

Can I just build an amp, hook the appropriate power solar cells (is it as simple as soldering the positive and negative from the cells to the positive and negative of the circuit?), and toss in a seperate solar battery charger circuit with a switch that would switch from the solar cells to the (now charged!) batteries?  Is it really that simple?  In concept, I mean.

And any ideas on a simple schematic for the amp section?  It just needs to be a bit louder than an unamplifed, flat picked acoustic guitar and an average volumed singer -- just to help her cut through the chatter of kids.

Thoughts or am I in over my head?
-Joe

[gez]

As far as solar panels go, don't know anything about them.  However, a back of envelope calculation (and I'm knackered, so I might have got muddled!) tells me that into an 8 ohm load, you'd need more than 18V to get 10W.  About 25V - 26V (more in practice as output swing of the amp won't be rail-to-rail).  Would need over an amp of current too.

IMO, rechargeable batteries would be a better idea. 

[jakehop]

You'll need a battery anyways, as the solar panels do not output a constant voltage. Try to find the most efficient speaker possible. The more efficient the speaker is, the less power the amplifier needs to output.

Jake

[Joe Hart]

Okay.  That answers one huge question (feasibility).  So say I used a rechargeable sealed lead-acid battery (like for alarm systems) that was 12W and 1.3 Ah (and I could use two if need be -- I don't specifically need a 10W amp, I was just using that as a basic starting point -- and I do realize that speaker efficiency is a BIG part of the overall volume), how long would it take to recharge one and how much power from the solar panels would I need to do this?  Basically, are we talking a whole bunch of panels and 8 + hours of sunlight to charge it so it would run for a measly hour?  That really doesn't seem worthwhile!  Or would a 5W amp with a very efficient speaker be loud enough (like the volume of someone yelling -- 60db -- just enough so she doesn't have to scream the songs!)?  I would guess that this would lower the power needs in half-ish?

If this is not a good idea, then what amp circuit should I use with rechargeable batteries?  The Little Gem is 1/2W and the Mk II is 1W.  I don't know if the Ruby is more than 1W.  I would guess that running it on 12V would deliver a little more power, but again, my E.E. knowledge is pretty much nonexistent!  Although I would like to go the solar route just for the sake of saying that I did it, even if it's only a solar charger for the batteries.

Any further thoughts?

Thank you very much for the info so far!!
-Joe

[earthtonesaudio]

Just a simple LM386 based amp (Ruby, Little Gem, Noisy Cricket) would do the trick with a 9V battery and an efficient speaker.  You'll get up to/over 100dB from a guitar speaker for sure.  By the way, 70dB corresponds to speech at 1 foot distance.

You could probably have a small (10" plus horn) PA speaker, and build a little flap of solar panels on a hinge on one side.  While playing, you'd open the panel out and let it soak up rays, but during transport you could close it and protect the solar cells.  Stick a motorcycle battery inside the speaker enclosure, along with the amp and circuitry, and all you'd have to connect are signal cables.

I don't know how long a charge would last (depends on how loud you play/how long etc) but the solar would help extend the time a good amount (depending on the sun).

Now I want to make one, darn it.  As if I have time for that.




FYI, Loudness vs. Decibels:

[rotylee]

http://en.wikipedia.org/wiki/Supercapacitor
http://www.maxwell.com/ultracapacitors/

Ultracapacitors can enhance the life of a battery, when used in conjunction with the battery as it absorbs and protects against any sags and surges in the voltage that could damage or limit the battery. Thus ultracapacitors are ideal for a wide range of consumer electronic products.

Renewable energy source such as wind, solar, water are quickly realizing the need for a superior energy storage devices. Due to their high reliability, efficiency and operating lifetime, ultracapacitors are especially ideal for renewable energy applications.

under case studies see
Datawell's Ocean Buoy ultracapacitor assisted solar power system
http://www.maxwell.com/ultracapacitors/applications/case-studies.asp
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=7,239,206.PN.&OS=PN/7,239,206&RS=PN/7,239,206
http://www.rockfordfosgate.com/products/photos/T15kW_3_l.jpg

[Joe Hart]

The decibel level that I used was just from a quick Google search.  I thought everything on the internet was true fact!  Very disillusioning!

Earthtonesaudio, your post makes me think it is quite possible!  Thank you for that!

So, now my question is this:  can I just build a Ruby (or something), have a solar powered battery charger with the battery hooked in like it's charging, and just tap the power off of the battery terminals?  In other words, panels to charger circuit (which includes a diode to prevent the battery from draining out the wrong way) to battery plus Ruby circuit (so the Ruby is wired in parallel with the battery).  Would this work?  I'm thinking that the amp would pull power from both the panel and the battery therefore keeping things somewhat constant and on a sunny day the battery would even be charging (perhaps slowly) while the amp is actually in use?  Or would I just have to charge the battery, then actually switch the battery out of the charging circuit and into the amp circuit (with a hard wired switch -- not physically moving the battery back and forth)?
-Joe

[Joe Hart]

Rotylee, very interesting!  Even the name sounds cool -- ultracapacitors.  Futuristic!  But I think I'll have to re-read a few of those articles (and have my dictionary handy!) to really understand what's going on with them.

Maxwell even sells a powerpack setup that may be just the thing.  One issue, though.  It seems that they cost about $140.00.  But maybe I'm missing something and they can be had much cheaper?  If they are this expensive, then it's out of my budget for this project.  Thoughts on this?
-Joe

[Nasse]

For speaker and amp I would try something like Eminence Beta 8"  with a piezo in a light plywood box, or "line array" column of five small fullrange speakers in a tall slim vertical box. For amp I would use TDA7370 car amp chip or similar, it has "bridged" configuration inside so it can give 2x22 watts with 12 volts or nearly so. Dunno how she will power the mixer or mic preamps if she has one.

I built small horn-loaded pa boxes with 12" driver last summer and they are quite loud and lightweight but perhaps too much for a lady

Ready made portable solar power packs seems to be silly expensive. I think I saw an ad of 12 volt 0,5 watt panel for less than 10 euros somewhere

[geertjacobs]

Our guitar player just bought a Roland micro cube that can run on batteries.
If you can build a solar charger for that...

[demonstar]

First off, the other day in town I saw a busker singing with a mic and electroacoustic through a marshall acoustic amp. He was powering it from a lead acid battery through an inverter. She could go for a option like this. Lead acid battery could even be charged by solar cells at home on days when not busking and charge it from the mains if it's not sunny.

If you go for the lm386 based project you could just power it off a battery pack of AA. My noisey cricket runs off a 6xAA battery pack and it would have plenty battery life for what you're after. In my opinion the volume through my 4x12 would be fine as i think it's actually pretty loud. I think it's got an impedance of 16ohms. The 6 batteries could be rechargeable and you can even get little solar chargers.

"http://www.maplin.co.uk/search.aspx?MenuNo=13001&MenuName=Solar+Battery+Chargers&FromMenu=y&doy=21m5"

Top and third one down were the ones I noticed.

[jakehop]

Joe, if it was me, I would make a sort of trolley-cart. The base consists of one or two car batteries, and the top of the speaker + amp. It would be pretty heavy, but the trolley-construction would help with that a lot, as it would be easy to drag around. Those batteries can last for quite some time! We use them for our big sound system in our camp at Roskilde Festival each year, and we can get hours of serious party volume out of a single battery. I believe they store a 40Ah charge at 12V, which equals 48 watts of power for 10 hours! So one might be more than enough.

Then, look at making a charger built in, so I can be plugged into a wall wart and recharged.

Jake

[gez]

Joe, if it was me, I would make a sort of trolley-cart. The base consists of one or two car batteries, and the top of the speaker + amp. It would be pretty heavy, but the trolley-construction would help with that a lot, as it would be easy to drag around. Those batteries can last for quite some time! We use them for our big sound system in our camp at Roskilde Festival each year, and we can get hours of serious party volume out of a single battery. I believe they store a 40Ah charge at 12V, which equals 48 watts of power for 10 hours! So one might be more than enough.

Then, look at making a charger built in, so I can be plugged into a wall wart and recharged.

Jake

+1.  A lot of buskers I see in London have converted little shopping trolleys to carry a power supply.  They usually fire up small practice amps.

There was a project in EPE magazine last year that was a reprint of a Nuts and Volts article.  A portable amp using a rechargeable cell that was hooked up to the mains.  The amp was one of the class D chips.  It had a power-saving mode that was enabled by one of its pins.  By using a follower with quick attack (and a comparator afterwards, I dare say), the amp only ran at full juice when a signal was present.  These circuits are usually lifted from the data sheets.  If I get some time in the next couple of days I'll dig out the article and link you to the data sheet for the chip and the cell they used.  Best I can do, I'm afraid.

[gez]

Can't find the damn artice!  Must have misfiled it.  Hope I haven't thrown it out! 

Had a look at EPE mag's website and the amp was called the "PortaPal Portable PA system".  It was in the March (schematic and explanation) & April (layout and construction tips) 2006 editions.  Blurb here:

http://www.epemag.wimborne.co.uk/projects2006.html

If you click on March it says it used the "Philips TDA1562Q" and a "12V d.c. sealed lead acid (SLA) supply".

No back issues left, but they'll photocopy it for a few quid:

http://www.epemag.wimborne.co.uk/acatalog/EPE_online_catalog_Back_Issue_Reprint_Service_16.html

Just Googled it and it was in Silicon Chip originally (not Nuts and Volts).  Now available to buy:

https://www.siliconchip.com.au/cms/access/purchaseRequired.html?buy=A&id=30295

https://www.siliconchip.com.au/cms/access/purchaseRequired.html?buy=A&id=30307

Default price seems to be Aussie dollars, so you'll need to select currency of choice from the pull-down list.

Edit:  PS, although it says it's a 70W (or whatever) amp, the design doesn't (can't) deliver that much power (they acknowledge this in the blurb, IIR).

[jakehop]

I'm with Gez on this one. The LM-series chips are definitely worth trying, as they are power efficient and very good. I've built a couple of monitors with integrated 2x35W amps, using two LM3875's for each monitor. They work great, but have higher power requirements than what a single car battery can offer. Take a look at this page:

http://www.national.com/cat/index.cgi?i=14

There you can see which chips National makes, that might be useful (and easy to acquire) for your project. If nothing seems useable, check out this link:

http://tinyurl.com/6m88zq - the TDA7490LSA might be interesting!

Jake

[Minion]

I say get a class D Module and Power it from a 12v battery...Class D amps are up to 90% efficient as opposed to a Class B amp which might be 50% if you are lucky and less for class A/B and Class A.....This means Much less Power consumption and much longer battery life...The problem with Class d is they are pretty much impossible to DIY but I have seen class d modules on E-bay that are pre-built boards for very cheap...

Also with a sencitive speaker you don"t need a lot of power.....20w into a 90db speaker would be as loud as 10w into a 93db speaker, and 10w into a 96db speaker would be twice as loud as 20w into a 90db speaker....

Cheers

[frank_p]

Our guitar player just bought a Roland micro cube that can run on batteries.
If you can build a solar charger for that...

The Microcube last 20 hours on six AA batteries
But its speaker last two weeks of playing...

[gez]

The problem with Class d is they are pretty much impossible to DIY but I have seen class d modules on E-bay that are pre-built boards for very cheap...

I spent some time messing around with Class-D amps a few years ago and developed a love-hate relationship with them.  Although they're pretty efficient, they fall at the last hurdle in that some of the output is dropped across the inevitable LC network that filters the carrier signal.  Even if the inductor has low resistance, so does the speaker load it forms a divider with.    This usually means you have to up the supply voltage to get the calculated output you were expecting, or leave it as is (if you have no choice) and put up with less gain.  All that work for nothing!  It's a shame as, in their favour, Class-D amps are incredibly quiet and tick-over current is/can be very low.

[gez]

They work great, but have higher power requirements than what a single car battery can offer.

Yeah, that's the downside of the design I linked to.  As I mentioned, though, I'm pretty sure they acknowledge this in the text...somewhere...in the small print. 

[jakehop]

Yeah, that's the downside of the design I linked to.  As I mentioned, though, I'm pretty sure they acknowledge this in the text...somewhere...in the small print. 

In my experience, the IC itself can be swapped in and out of the designs, as long as one checks for any deviation in the IC's datasheets, so I'll say it's good information still. I really hope this project is finished. If so, pictures and/or video of the singer using it is mandatory! 

Jake