coin cell for axe120
- Thread starter coin12
- Start date
Coin cells are only for low current stuff. You will kill them pretty quickly I would have thought.
I'll leave others to provide long detailed posts about coin cell capacities and maximum current loads and running them in series (and as an aside, parallel too) etc.
I would suggest that you get some info (i.e. the DATA SHEETs) on coin cells and look at their specs re: the above.
PLEASE read up on them especially mAh capacities and current limits. It IS important. Then measure the electrical specs of your little bot and dig out your calculator.
Could you use 4 x AAAs and suffer the reduced runtime? I have no experience with that product. Maybe there are some other battery options too. Or even some other weight-loss options.
I'll leave others to provide long detailed posts about coin cell capacities and maximum current loads and running them in series (and as an aside, parallel too) etc.
I would suggest that you get some info (i.e. the DATA SHEETs) on coin cells and look at their specs re: the above.
PLEASE read up on them especially mAh capacities and current limits. It IS important. Then measure the electrical specs of your little bot and dig out your calculator.
Could you use 4 x AAAs and suffer the reduced runtime? I have no experience with that product. Maybe there are some other battery options too. Or even some other weight-loss options.
westaust55
Moderator
If you are looking at something like the CR3032 coin cells then the answer is NO.
While these cell have a capacity of 0.235mAh there is a max continuous current draw of 3mA whereas the AXE120 with motors loaded at say 66% will draw around 200mA.
Since you say the motors are having trouble moving the micro-bot suggests the load is more like 100% or 300mA or more
While these cell have a capacity of 0.235mAh there is a max continuous current draw of 3mA whereas the AXE120 with motors loaded at say 66% will draw around 200mA.
Since you say the motors are having trouble moving the micro-bot suggests the load is more like 100% or 300mA or more
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Mmmm- "too heavy to run"- sounds like the infamous R101 1930 hydrogen airship that became rain soaked & crashed en route to India. It transpired, along with all the food & -ah-considerable drink demanded by a colonial journey, that such extra trifles as a piano had been stashed aboard. Hence can you jettison some baggage maybe?
For improved power/weight of course look to cell phone style Lithium ion/polymer secondary cells. Most are 3.6V & ~800mA.h & weigh just ~20 grams, and can delivery almost evil currents-for a while. Larger versions of these are very popular with R/C model aircraft fanatics, but special chargers are essential. I recently watched such a plane aloft & it sounded like an aerial F1 racer, with performance over 15 mins that near defied the laws of electrochemistry
EXTRA: Dippy- your every wish is my command.
For improved power/weight of course look to cell phone style Lithium ion/polymer secondary cells. Most are 3.6V & ~800mA.h & weigh just ~20 grams, and can delivery almost evil currents-for a while. Larger versions of these are very popular with R/C model aircraft fanatics, but special chargers are essential. I recently watched such a plane aloft & it sounded like an aerial F1 racer, with performance over 15 mins that near defied the laws of electrochemistry
EXTRA: Dippy- your every wish is my command.
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westaust55
Moderator
More on why not to use the CR3032 coin type cells:
With a load of 300 mA, notwithstanding the nominal 3mA limitiation, the load resistance is effectively of the order of 10 Ohms.
Like all batteries, the actual capacity drops with high current draw and in this case would by extrapolation of the curves drop to something like 80mAh at 23deg C. That would equate to a running time of something like 15 minutes.
As Dippy has suggested, try using some AAA batteries.
EDIT:
or as Manuka has suggested a Lithium Ion battery. here is one the size of an AA cell ? ? ? (or could be longer) with 940mAh rating that can deliver 1.8Amps.
With a load of 300 mA, notwithstanding the nominal 3mA limitiation, the load resistance is effectively of the order of 10 Ohms.
Like all batteries, the actual capacity drops with high current draw and in this case would by extrapolation of the curves drop to something like 80mAh at 23deg C. That would equate to a running time of something like 15 minutes.
As Dippy has suggested, try using some AAA batteries.
EDIT:
or as Manuka has suggested a Lithium Ion battery. here is one the size of an AA cell ? ? ? (or could be longer) with 940mAh rating that can deliver 1.8Amps.
Please have a look at http://www.megabatteries.com/item_details.asp?id=14267&cat_id=51
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Rickharris
Senior Member
If you don't need extended freedom - and most robots run on the table or room floor then why no remove the power supply and fit a suitably length of wire to supply power - the robot will trail it's umbilical quite happily.
thxx guys alot i think the li- ion is good the robot work at 6v so two 3.7 batt will be around 7.4 v i think its not going to damage the circuit ..or using 9v battery i dont know which is lighter 9v battery or two cells of 3.7 li-ion
well the problem of weight came becoz of i added a xbee module over the top of the robot to make wireless comunication and the batts of the xbee also over the robot including the robot pcb ,robot 4-AAs , line tracker ultrasonic range finder so the robot is completly dead
im thinking to replace 4AA's with one 9v batt (maybe i'll add a resistor to decrese the voltage ) and using a second 9v batt for the xbee
i dunno which is lighter one 9v battery or two of 3.7 li ion if two of 3.7 is lighter im going to use them if they are the same weight as 9v .... 9v is cheaper
well the problem of weight came becoz of i added a xbee module over the top of the robot to make wireless comunication and the batts of the xbee also over the robot including the robot pcb ,robot 4-AAs , line tracker ultrasonic range finder so the robot is completly dead
im thinking to replace 4AA's with one 9v batt (maybe i'll add a resistor to decrese the voltage ) and using a second 9v batt for the xbee
i dunno which is lighter one 9v battery or two of 3.7 li ion if two of 3.7 is lighter im going to use them if they are the same weight as 9v .... 9v is cheaper
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inglewoodpete
Senior Member
I don't think you've fully grasped the concepts of batteries.
If you're talking about a 9v transistor radio battery (PP3 or 216 etc), then it won't have the capacity to run a robot. They don't have the capacity to run very much for very long at all. Even an Alkaline 9v battery can only provide a limited amount of current.
That's what had me wondering. While a resistor will limit the current and consequently drop the available voltage, it offers no regulation of the output voltage if the current demand varies. It also wastes energy as heat (Heat = Watts (Power)= Vdrop x Current) - not what you really want when using batteries.
inglewoodpete
Senior Member
Lithium Ion offers among the best energy-to-weight ratios for batteries and can supply quite heavy currents. However, that are not cheap to buy and require a purpose built charger (they are dangerous if not charged with the correct charger).
If you have one, you can reuse an old mobile phone (cellphone) battery and charger for this purpose.
If you have one, you can reuse an old mobile phone (cellphone) battery and charger for this purpose.
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marcos.placona
Senior Member
The best choice here would be to use 3 alkaline batteries. they are cheaper, and will last much longer than a 9v battery.
Li ion batteries are good, but you will need to take some special care with them (don't let them go totally "dry" for example).
AA or AAA batteries are the easiest for robots, as they will last much longer than a normal battery, and you don't need any really special care (except change them when they "die").
If you decide to stick to the Li Ion batteries, I'd recommend you using a regulator (if you're using two batteries), as they will provide you 3.7v * 2, which is 2.4v more than the picaxe can support, and will easily fry it.
The 7805 regulator will probably be the hero here
And also, you need to think of a way to control the charge of your batteries, 'cause as I stated before, Li Ion Batteries are a bit sensible, and will be damaged if not treated properly (read go totally dry)
The coin cells would fail immediately. It simply would not work. The important factor is the internal resistance. This is like a resistor in series with the battery voltage but inside the battery. That’s why the terminal voltage drops on any battery when you apply a load. With a battery as puny as a coin cell, the internal resistance will be so high that as soon as you energise one of the motors, the terminal voltage will drop to well bellow the minimum for a PICAXE to work. And the motor will probably not even turn. The first rush of current to a starting motor is its Stall Current. Even with a small efficient motor, this is likely to be over 500mA.
You can measure the internal resistance of a battery using a multimeter and ohms law thus:
Measure the unloaded terminal voltage. (Vunloaded)
Put a known load (Rload) across the terminals and measure the terminal voltage again. (Vloaded)
Iload (Amps) = Vunloaded (volts) / Rload (Ohms)
Vdrop (Volts) =Vunloaded (Volts) – Vloaded (Volts)
The current flowing through the external load resistor (Iload) is also flowing through the internal resistance, like a voltage divider. Vdrop is the voltage dropped across the internal resistance for the test load. So:
Rinternal (Ohms) = Vdrop (Volts) / Iload (Amps)
As a rule of thumb, the heavier the battery, the lower it’s internal resistance, and rechargeables are usually lower still. You will probably face a similar problem with a PP3 (9v).
With motors, unless they are particularly efficient, you are unlikely to get away with anything smaller than AAAs.
You can measure the internal resistance of a battery using a multimeter and ohms law thus:
Measure the unloaded terminal voltage. (Vunloaded)
Put a known load (Rload) across the terminals and measure the terminal voltage again. (Vloaded)
Iload (Amps) = Vunloaded (volts) / Rload (Ohms)
Vdrop (Volts) =Vunloaded (Volts) – Vloaded (Volts)
The current flowing through the external load resistor (Iload) is also flowing through the internal resistance, like a voltage divider. Vdrop is the voltage dropped across the internal resistance for the test load. So:
Rinternal (Ohms) = Vdrop (Volts) / Iload (Amps)
As a rule of thumb, the heavier the battery, the lower it’s internal resistance, and rechargeables are usually lower still. You will probably face a similar problem with a PP3 (9v).
With motors, unless they are particularly efficient, you are unlikely to get away with anything smaller than AAAs.
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Well, I'm not going to start prolonged threads about batteries as I think it'll confuse rather than educate at this stage - coin is in a big hurry.
But I am a bit surprised the robot is totally ached innit.
Coiny said "xbee also over the robot including the robot pcb ,robot 4-AAs , line tracker ultrasonic range finder so the robot is completly dead"
So, if I understand that correctly it's AXE120 kit +XBEE + U/S rangefinder + Line tracker pcb. Are we just talking the little pcb-based modules here? Robot Dead? Are they that heavy? This is why I'm surprised.
I think I'd try 4 x AA NiMHs and bypass the diode - taking into account warnings in the AXE120 Data Sheet re: the diode.
But I am a bit surprised the robot is totally ached innit.
Coiny said "xbee also over the robot including the robot pcb ,robot 4-AAs , line tracker ultrasonic range finder so the robot is completly dead"
So, if I understand that correctly it's AXE120 kit +XBEE + U/S rangefinder + Line tracker pcb. Are we just talking the little pcb-based modules here? Robot Dead? Are they that heavy? This is why I'm surprised.
I think I'd try 4 x AA NiMHs and bypass the diode - taking into account warnings in the AXE120 Data Sheet re: the diode.
westaust55
Moderator
AXE120 power options
Coin12 stated in his first post ”I have axe120 microrobot it runs with 4 AA batteries”.
And direct from the AXE120 datasheet:
Two 3.6/3.7 V Li-ion batteries will help keep the power up but as others have indicated a 7805V regulator will be needed for the PICAXE chip to prevent from damaging that.
A possibility could be 3 x 3.6 V Li-ion cells and two regulators:
- 7805 regulator for 5Vdc for the PICAXE side,
- 7809 regulator for the XBEE if that runs of 9 volts (not familiar with XBees)
- As the L293D can handle up to 36V, modifiy the PCB and run the motors across 2 Li-ion cells for 7.2 Volts. Could the motors handle 3 Li-ion cells at 10.8V ? Certainly more likely to burn out.
This will reduce the battery set to 3 cells instead of one or two sets of 4 AA’s (depending how XBEE powered at present), It would mean some serious mods to the AXE120 robot PCB.
PLUS the need for proper charging of the Li-ion batteris as others have already mentioned.
Coin12 stated in his first post ”I have axe120 microrobot it runs with 4 AA batteries”.
And direct from the AXE120 datasheet:
Dropping to 4 x Ni-MH AA’s giving around 5.00 V after removal of the “safety” diode on the AXE120 will be slightly worse as the motor volts will be down and torque is proportional to the square of the voltage. If down from 5.3V (6V-0.7V for diode) to 5V (94%) reduces torque by 12% compared to a fresh set of alkaline 1.5V AA’s.
Two 3.6/3.7 V Li-ion batteries will help keep the power up but as others have indicated a 7805V regulator will be needed for the PICAXE chip to prevent from damaging that.
A possibility could be 3 x 3.6 V Li-ion cells and two regulators:
- 7805 regulator for 5Vdc for the PICAXE side,
- 7809 regulator for the XBEE if that runs of 9 volts (not familiar with XBees)
- As the L293D can handle up to 36V, modifiy the PCB and run the motors across 2 Li-ion cells for 7.2 Volts. Could the motors handle 3 Li-ion cells at 10.8V ? Certainly more likely to burn out.
This will reduce the battery set to 3 cells instead of one or two sets of 4 AA’s (depending how XBEE powered at present), It would mean some serious mods to the AXE120 robot PCB.
PLUS the need for proper charging of the Li-ion batteris as others have already mentioned.
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