| Author | Message | ||
     linda R. |
hey simon, i'm trying to make the simple steam boat which uses the empty soda can, but i couldn't find the copper tubing as small as the one you made. i tried using the bigger one but it seemed to affect the speed. i'm trying to make a simple toy, one like the boat, but most of them on your site needs a lot of stuff that i couldn't find here in singapore. so please help or my teacher will kill me! this is really urgent! (by the way, i'm 13, so my mum wont allow me to buy anything from the catalogue). | ||
| Anonymous |
If there are any hobby stores near you, they usually carry bendable tubing similar to what is needed for the project. | ||
| juma salih |
I need to know whit is the cost of the toys | ||
| zake |
need to know whit is the cost new | ||
| t_rey1995 Unregistered guest |
how to build van de graph generater for science fair | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 122 Registered: 12-2004 |
See this page. | ||
| physics boy (Physicsinaction) Junior Member Username: Physicsinaction Post Number: 7 Registered: 7-2006 |
Can please anyone help me I want to build a circuit having led connected to 12 volt 195 amp battery . The led goes out if current in the battery falls to 150 amp. I think a lot about it but I don`t seem to get anything can anyone help me out with this circuit. | ||
| Alex Roberts (Whoo_mythbusters) Senior Member Username: Whoo_mythbusters Post Number: 130 Registered: 9-2005 |
First off, do you mean 195,and 150 milliamps? I would think so. Second, how big is the LED, or are there multiple LED's, also if there are more than one, how are you connecting them series or parallel. Is the battery a rechargeable battery or not? Are you using any resistors? When you first connect the LED to the battery does it get hot really fast, if it does you are probably using too strong a battery. | ||
| physics boy (Physicsinaction) Junior Member Username: Physicsinaction Post Number: 8 Registered: 7-2006 |
Actually Led I am using is a normal 3 volt LED The battery is of 12 volts so i am using a resistor in series before led to get 3 volts to LED. Now the problem is what I have to do next in order for led to go off when my battery`s current drop down to 150 amp . And also my battery that I am using is a rechargeable battery. | ||
| James (Magnets) Intermediate Member Username: Magnets Post Number: 40 Registered: 6-2006 |
150 amps??? What type of LED are you using? If you want to power the LED just use 2 AA batteries. Most AA batteries are 1.5 volts and 1 AA battery alone can usually supply enough amps to power a LED. | ||
| Alex Roberts (Whoo_mythbusters) Senior Member Username: Whoo_mythbusters Post Number: 131 Registered: 9-2005 |
James, I don't think that is what he is asking. Physics, so you are wanting the Led to turn off when the current on your battery drops to a certain level. One way, although it might not be the best, is to modify an ammeter, the older kind with a needle, to disconnect the circuit to the LED. You would have to put a contact on the needle and then a certain length of wire on the back of the meter so when the needle is above a certain value the circuit is still closed, but when it drops below that level the circuit becomes open and the LED turns off. | ||
| Michael (Michaelt) Advanced Member Username: Michaelt Post Number: 82 Registered: 12-2005 |
Usually the state of charge of a battery is determined by its voltage, not its amperage. Car batteries, although nominally 12V, are about 12.6V "float" (unloaded) voltage when fully charged. The battery is considered fully discharged when it produces about 10.5V under load. An ammeter placed across the terminals of a 12V battery will essentially short-circuit it -- an ammeter is used to measure the amount of current flowing through a circuit, not to measure the capacity of a battery. | ||
| physics boy (Physicsinaction) Junior Member Username: Physicsinaction Post Number: 9 Registered: 7-2006 |
Thankyou very much every body for help I really appreciate that and especially Michael thankyou your answer really provide a great help. | ||
| Alex Roberts (Whoo_mythbusters) Senior Member Username: Whoo_mythbusters Post Number: 143 Registered: 9-2005 |
I was aware that it did not measure the capacity of the battery, I was just supplying an answer to his problem, the Led and battery might have been an indicator in a completely different circuit. | ||
| Michael (Michaelt) Advanced Member Username: Michaelt Post Number: 84 Registered: 12-2005 |
Alex, One could use the LED and ammeter to signal when a particular circuit was drawing more amps than some arbitrary value such as maybe signaling when an electric motor is working harder than normal (by drawing more current), or maybe to indicate when an electric motor was using less current (by lighting the LED when the current draw was lower than expected. It was common for cars in the 60's to have an ammeter connected such that you could tell whether the battery was charging or discharging or just 'floating' depending on the direction the needle was pointing in. It was good for indicating whether you were drawing more current than the alternator could provide (as the needle would swing towards "D" for "discharging") or if the battery were being charged heavily such as after starting the car after discovering that you'd left the headlights on for an hour (as it would point to the "C" for "charging".) In some cases, a weak battery may cause the ammeter to show a constant charging state when the engine is running -- but not always. With the engine off, the needle will still go to the neutral position (as long as there aren't any other electrical demands.) Don't forget that the low-battery indicator circuit itself also uses power! Physicsboy: I did some googling for you (google is your friend) and found an article on the design of battery power indicators: http://www.edn.com/article/CA318716.html?text=fleapower Of note is that this article also discusses using voltage, not current, to determine how fully charged a battery is. | ||
| I. Dimov (Overrider) Advanced Member Username: Overrider Post Number: 99 Registered: 12-2005 |
Exactly, in a similar fashion to capacitors, a battery's voltage drops as time increases, and charge decreases, although not as abruptly as capacitors. AFAIK this is one of the reasons, that batteries are used as PS instead of high capacitance capacitors. |
