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Old 26th August 2011, 12:09 AM   #1
mimoose is offline mimoose  United States
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Default 12 volt system w/o alternator

for 12v audio systems. how does one factor out the alternator. my bike audio system doesnt have one, and a bike generator does generate anything of importance.
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Old 26th August 2011, 12:20 AM   #2
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factor in a big battery.

Or an I-pod
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Old 26th August 2011, 04:07 PM   #3
mimoose is offline mimoose  United States
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well, not sure what you mean, but it will be a speaker system for a bike computer or a mp3 player and not the usual reciever-cd player. i was just wondering if there are any different rules i should know about when factoring in calculations. i vaguely remember some kid on youtube having a bicycle audio system that included an enormous capacitor, but i cant find the clip and again and i dont know how it fits into the system.
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Old 26th August 2011, 11:07 PM   #4
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How long do you expect the system to play between chargings?

How much amplifier power do you think you'll be using?

Forget about the capacitor.
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Old 27th August 2011, 06:22 AM   #5
mimoose is offline mimoose  United States
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i was hoping for 3 hours play time between chargings and about 200 to 300 watts for my whole system. i still dont understand a lot of these audio terms, i just starting to learn about audio electronics. thanks for responding!

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Originally Posted by Perry Babin View Post
How long do you expect the system to play between chargings?

How much amplifier power do you think you'll be using?

Forget about the capacitor.
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Old 27th August 2011, 09:18 AM   #6
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lordy.

Lets inject some terms you may understand. 300 watts is the best part of half a horsepower in old money. In a twelve volt system, it means you will be draining almost 25 amps constantly from your power supply. That's similar to running six headlights at once in your car. Don't know about you, but my car battery wouldn't last 3 hours doing that, and it weighs best part of 35lb.

Unless you can compete in the tour de France at a top 5 level, you are incapable of generating this amount of power yourself, most humans peak at around 200 watts in a burst.

You are either grossly overestimating your system's capabilities, or grossly underestimating the power supply requirements - I'm not sure which since you seem not to know what you really mean.

I'm not even sure what you mean by "bike" - bicycle, or motorcycle?

How about you describe in detail what you would like to do, and then we can give some realistic advice. Hopefully, you will get something that works for you at the end.
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Old 27th August 2011, 09:58 AM   #7
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You'll likely need between 100 and 120 amp-hours off capacity. That's likely to be about 100 pounds. Dry cell will probably be the best choice but they're expensive. The cheapest would be deep cycle marine batteries but they're going to be heavier. Standard batteries will work but won't survive repeated deep discharging.

Of course, all of this depends on the actual current drawn (which depends on the output level, and the efficiency of the system) and the time it's being driven hard.

If you can afford them, a full range class D amp will be more efficient than a class B or class AB amp, but will be more expensive.
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Old 27th August 2011, 12:45 PM   #8
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oh, ah, that is one thing to concider- your power supply. standard lead acid batteries are rated between 13 and 54 discharges before they are spent. dry cell, or even caps can survive constant cycling, but caps, are something like 1/1000'th of what an actual battery can hold for the size, even if you do large packs of smaller caps. you mentioned in your trike thread about your motor- i am not real familiar with the thing. i'm assuming it's a small gas motor, like 2hp or so. it likely has a flywheel magnet that runs across a pickup coil. perhaps you can find a way to get a spare, and mount it in another spot on the case, and severly under-wrap it at higher gausge wire. obvuisly, it would be trial and error to get it in the range you want, but i would immagine you want about 16-18v pulsed on step, and you can run that to a cap/choke and install an atv voltage regulator. likely it is going to need to be run through a key, which also could activate the system, to keep it from back-draining the battery in storage.... just an idea
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Old 28th August 2011, 01:35 PM   #9
mimoose is offline mimoose  United States
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thanks for clarifying that for me. 300 watts is a stupid goal. in fact i did do the calculation after posting and realized 25 amps is unreasonable.
actually i am building a trike
LodeRunner Cargo Trike - YouTube
i had posted a seperate topic:
6-speaker system for trike

i am designing the box that will sit behind me, i want to embed the woofer in the back and embed the midrange speakers in a fiberglass seat.
perhaps 75-150 is more realistic, wish there was an effective bike generator i could put in the system. right now i have to pay for my fiberglass and casting materials, i wont have my electronics lab up to build and test for weeks. (i have to do the fiberglassing now before the weather turns cold, detroit mi., so i have to figure out how my woofer and seat will look now with speakers in them. ) i think a motorcycle has an alternator, doesnt it? so basically since all the topics are geared towards vehicles with alternators, i wanted to find out what kind of system is realistic without that current source.
Quote:
Originally Posted by aardvarkash10 View Post
lordy.

Lets inject some terms you may understand. 300 watts is the best part of half a horsepower in old money. In a twelve volt system, it means you will be draining almost 25 amps constantly from your power supply. That's similar to running six headlights at once in your car. Don't know about you, but my car battery wouldn't last 3 hours doing that, and it weighs best part of 35lb.

Unless you can compete in the tour de France at a top 5 level, you are incapable of generating this amount of power yourself, most humans peak at around 200 watts in a burst.

You are either grossly overestimating your system's capabilities, or grossly underestimating the power supply requirements - I'm not sure which since you seem not to know what you really mean.

I'm not even sure what you mean by "bike" - bicycle, or motorcycle?

How about you describe in detail what you would like to do, and then we can give some realistic advice. Hopefully, you will get something that works for you at the end.
100 lbs!!! i will most definitely have to adjust my goals. i was hoping for more like a 7-8 lb LI-PO battery. i want to learn to design and build my amplifier. i keep reading class D is the best, i didnt know they are also more power efficient. it appears i will focus on that kind of circuit.
Quote:
Originally Posted by Perry Babin View Post
You'll likely need between 100 and 120 amp-hours off capacity. That's likely to be about 100 pounds. Dry cell will probably be the best choice but they're expensive. The cheapest would be deep cycle marine batteries but they're going to be heavier. Standard batteries will work but won't survive repeated deep discharging.

Of course, all of this depends on the actual current drawn (which depends on the output level, and the efficiency of the system) and the time it's being driven hard.

If you can afford them, a full range class D amp will be more efficient than a class B or class AB amp, but will be more expensive.
based on what the three of you have said, perhaps i should pick the battery i can afford in weight and expense and make a sound system around that.
i will be using an electric front wheel hub motor, my motor will need 3 batteries, lead acid batteries are out of the question, just too freaking heavy. LI-PO are much more expensive but lighter. i will have a separate battery just for my audio. actually i dont know if a LI-PO can run an audio system. i find audio electronics to be very confusing. i am not using a gas engine. those things make so much noise! sometimes i hear someone on one of those things in my neighborhood and you can hear them from blocks away! in fact, if i had chose a gas engine for my bike, i wouldnt even bother with a stereo system. its having a quiet hub motor that makes the thought of a multi-speaker stereo system captivating.
Quote:
Originally Posted by AKHeathen View Post
oh, ah, that is one thing to concider- your power supply. standard lead acid batteries are rated between 13 and 54 discharges before they are spent. dry cell, or even caps can survive constant cycling, but caps, are something like 1/1000'th of what an actual battery can hold for the size, even if you do large packs of smaller caps. you mentioned in your trike thread about your motor- i am not real familiar with the thing. i'm assuming it's a small gas motor, like 2hp or so.

i understand a little bit of what you said, like 30%. i mean i understand on the face of it, (except what you mean by "key"), i just dont know if it will work. what i am going to have to do is go to the ebike forum endlessspere and see what the latest on bicycle generators are. btw, i havent gotten many ideas for stereo systems on that forum, most just use...i've forgotten that quick, but nothing interesting, half headphones or something.

Quote:
it likely has a flywheel magnet that runs across a pickup coil. perhaps you can find a way to get a spare, and mount it in another spot on the case, and severly under-wrap it at higher gausge wire. obvuisly, it would be trial and error to get it in the range you want, but i would immagine you want about 16-18v pulsed on step, and you can run that to a cap/choke and install an atv voltage regulator. likely it is going to need to be run through a key, which also could activate the system, to keep it from back-draining the battery in storage.... just an idea
anyway, the answer based on your comments is select the battery that will give me the most amp/hours and charge cycles with the least amount of weight that i can afford and build the system from that wattage. do most people do that? anyway,thanks folks!
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