The issue with rechargeables is that they have less voltage than Alkalines.
So, 4 alkalines, at 1.5 volts each, is 6 volts.
4 NiCd's, or 4 NiMh's, have 1.2 volts each when fully charged. 4 x 1.2 == 4.8 volts. Well, 4.8 volts is below the 5.5 volts the BOE board regulator needs. So, you can add a battery -- 5 x 1.2 == 6 volts (neat, huh?). Now you just have to find a place to put the 5th battery.
I think NiMh (Nickel-Metal Hydride) batteries have no 'memory', hold their charge pretty well, and hold more charge than a NiCd.
·· I rigged an extra battery holder in series on my Boe-Bot to get 6 volts with rechargeables.· It works fine.· (Fits under the Boe just over the tailwheel and still has room go get the cell in and out.· I used double faced tape to hold it to the chassis)
I use the Ray-O-Vac rechargeable batteries, they charge up to 1.5V. Unfortunately Ray-O-Vac no longer carries these batteries, but I found a Canadian company,·Sundance Solar that carries a rechargeable 1.5V battery. When I start to get low on the batteries that I have, then I will have to give them a try.
Not only do the NiMh recharibles have less voltage, then generally have less useful life or AmpHours [noparse][[/noparse]without recharge].
Still, they can save money and work well in solar recharged devices.
If you want the best, a 7.4V Lithium Polymer with 2400mAH or higher is great. Lithium takes a quicker charge, not a 10-12 hour wait and is smaller. The 7.4 volt is optimal for most projects using a 7805 regulator.
It may be too high to directly run servo motors though.
Use a regulator or diode to bring the voltage down to 6.0Volts or under.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Hi, I have a somewhat-related question:
when should one use NiCd's and when should one use NiMH's?
As far as I know, NiCd's are cheaper, but NiMH's are less toxic.
Are there any performance-related differences that one needs to consider?
Current NiMh have capacities approaching those of Lithium Polymer - it's not uncommon to find 3300 mAh 7.2V NiMh battery packs and these can be recharged in 2-4 hours with a Smart battery charger. The advantage of NiMh over NiCd is they have much higher capacity and they don't suffer from the memory affect (where the batteries don't charge up fully until they're fully depleted). Lithium Polymer batteries can be tricky to recharge if you're building your own charger and they can explode if improperly recharged. Lithium Polymer have one advantage - they weigh a lot less than NiMh batteries.
Forrest said...
Current NiMh have capacities approaching those of Lithium Polymer - it's not uncommon to find 3300 mAh 7.2V NiMh battery packs and these can be recharged in 2-4 hours with a Smart battery charger. The advantage of NiMh over NiCd is they have much higher capacity and they don't suffer from the memory affect (where the batteries don't charge up fully until they're fully depleted). Lithium Polymer batteries can be tricky to recharge if you're building your own charger and they can explode if improperly recharged. Lithium Polymer have one advantage - they weigh a lot less than NiMh batteries.
Thank you for the info, Forrest.
Now that I am thinking about, I have some more "battery" questions:
- Why is it considered bad to leave rechargeable batteries in the recharger after they have been recharged?
- I notice that some of my rechargeable batteries quickly get very warm while they are recharging (especially 9V batteries). Why does this happen, and is this normal?
- I have a set of 4 AA rechargeable batteries (relatively new), where one of them loses its charge very quickly. The other three work OK. What is going on?
- Where does one buy Lithium Polymer rechargeable batteries? I only know about them being used in notebook computers. Are they available in the standard AA, AAA, 9V sizes?
- I would like to make a recharger that I could put on a small robot (like the BOE-Bot). Could anyone tell me how to make one, or point me to any schematics and/or instructions? I opened my store-bought recharger and it looks like it's just a wall-wart DC adapter connected to a resistor that then connects to the battery terminals. Is it the wall-wart that prevents the batteries from discharging? How does the recharger know when the recharging is completed (or, how do I make it shut off when it's done)?
Q. Why is it considered bad to leave rechargeable batteries in the recharger after they have been recharged?
A. Generally, they keep charging and this creates heat. Excessive heat will wear out your batteries quicker. Some charges now shut off, but not all.
Q. I notice that some of my rechargeable batteries quickly get very warm while they are recharging (especially 9V batteries). Why does this happen, and is this normal?
A. Some heat during charging is normal and some chargers work faster than others. If you have doubts, you should stop and check that the battery is right for the charger AND that it isn't swelling.
Any Swollen batteries are potential danger and should be discarded.
Q. I have a set of 4 AA rechargeable batteries (relatively new), where one of them loses its charge very quickly. The other three work OK. What is going on?
A. Ideally each and every cell should be charged alone, but many chargers work in pairs or other groups. If one battery is weak or defective, the charger merely responds by attempting to charge the group and the 'runt' looses out. In some cases, switching the batteries around helps. In some cases, you just have to accept that you got a bad battery - take it back and ask for a replacement.
Q. Where does one buy Lithium Polymer rechargeable batteries? I only know about them being used in notebook computers. Are they available in the standard AA, AAA, 9V sizes?
A. Physical chemistry creates the actual Voltage in a battery. Tradional flashlite batteries were all 1.5V, so many people think every battery should be like that. NiMh and NiCA are 1.2V. Lithium Ion batteries are in mutiples of 3.7volts. Since that have much higher energy density, when built as a sealed battery they have a greater ability to burst.
While there are some Lithium batteries shaped like conventional batteries, they won't simply replace an AA or a C cell. You can buy Lithium batteries and chargers at electronics supply house and R/C hobby stores.
Since there is a greater chance of bursting, a good Lithium charger is quite important. And since over-heating appears to quickly destroy the Lithium Polymer beyond recharge ability, the better chargers have thermal shut down.
In some cases, you will see Lithium batteries with their own 'thermal shut-down' and 'low-power' shut down. These actually have a circuit board attached and may explain why you see them rated at less than the 3.7volts.
Q. I would like to make a recharger that I could put on a small robot (like the BOE-Bot). Could anyone tell me how to make one, or point me to any schematics and/or instructions? I opened my store-bought recharger and it looks like it's just a wall-wart DC adapter connected to a resistor that then connects to the battery terminals. Is it the wall-wart that prevents the batteries from discharging? How does the recharger know when the recharging is completed (or, how do I make it shut off when it's done)?
A. Rechargers are getting more complicated everyday. Generally, I would strongly recommend you buy a Lithium Ion charger rather than make one as it is likely to be both cheaper and safer to do so and provide you better value.
Regarding the other types, Google for schematics.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
I wish I could get the forum to accept attached photos.. I made a NiMH pack from
an old cam-corder, into a rechargeable supply for the BOE.. I took a 5-cell Sub-AA
pack (2/3-height AA's,) and changed the OOOOO into a .....
O O
O O O -like stack. Took a couple of twist-ties (Ala-VEX, Sorry..), and mounted
it in place where the old battery pack used to be. So-far, brief use, the batteries haven't
been charged in 5 weeks! (brief use meaning 10-12 minute runs per week.) and they're
still full power.
Only drawback, the pack is so low in the frame, it only clears the rear ball-wheel by 1/4" , and the
ground by 1/2".
I haven't figured on how to make the BOE search-out a charger, but an interesting idea.
I have a few Gel cells. One is an 8volt 9Amp hour that I am looking forward to putting into a rolling bot.
The other two are 6volt 1Amp hour Gel cells. These little Gel cells are really useless. NiMh has more capacity, less weight and fits in battery holders. I may use them as 'backup power' but they were a complete waste of money.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Comments
So, 4 alkalines, at 1.5 volts each, is 6 volts.
4 NiCd's, or 4 NiMh's, have 1.2 volts each when fully charged. 4 x 1.2 == 4.8 volts. Well, 4.8 volts is below the 5.5 volts the BOE board regulator needs. So, you can add a battery -- 5 x 1.2 == 6 volts (neat, huh?). Now you just have to find a place to put the 5th battery.
I think NiMh (Nickel-Metal Hydride) batteries have no 'memory', hold their charge pretty well, and hold more charge than a NiCd.
·· I rigged an extra battery holder in series on my Boe-Bot to get 6 volts with rechargeables.· It works fine.· (Fits under the Boe just over the tailwheel and still has room go get the cell in and out.· I used double faced tape to hold it to the chassis)
Ray
Still, they can save money and work well in solar recharged devices.
If you want the best, a 7.4V Lithium Polymer with 2400mAH or higher is great. Lithium takes a quicker charge, not a 10-12 hour wait and is smaller. The 7.4 volt is optimal for most projects using a 7805 regulator.
It may be too high to directly run servo motors though.
Use a regulator or diode to bring the voltage down to 6.0Volts or under.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
when should one use NiCd's and when should one use NiMH's?
As far as I know, NiCd's are cheaper, but NiMH's are less toxic.
Are there any performance-related differences that one needs to consider?
Thanks!
Thank you for the info, Forrest.
Now that I am thinking about, I have some more "battery" questions:
- Why is it considered bad to leave rechargeable batteries in the recharger after they have been recharged?
- I notice that some of my rechargeable batteries quickly get very warm while they are recharging (especially 9V batteries). Why does this happen, and is this normal?
- I have a set of 4 AA rechargeable batteries (relatively new), where one of them loses its charge very quickly. The other three work OK. What is going on?
- Where does one buy Lithium Polymer rechargeable batteries? I only know about them being used in notebook computers. Are they available in the standard AA, AAA, 9V sizes?
- I would like to make a recharger that I could put on a small robot (like the BOE-Bot). Could anyone tell me how to make one, or point me to any schematics and/or instructions? I opened my store-bought recharger and it looks like it's just a wall-wart DC adapter connected to a resistor that then connects to the battery terminals. Is it the wall-wart that prevents the batteries from discharging? How does the recharger know when the recharging is completed (or, how do I make it shut off when it's done)?
I apologize for the many questions.
Any help is appreciated!
Thanks!
I buy all my batteries at Battery Space:
Last night I bought one of these for a Robot I'm working on:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2314
It has a 9.6 amp discharge rate, so hopefully it won't blow up if the robot stalls!
But, all their warnings about Lithium really scare me
Kenny
·
A. Generally, they keep charging and this creates heat. Excessive heat will wear out your batteries quicker. Some charges now shut off, but not all.
Q. I notice that some of my rechargeable batteries quickly get very warm while they are recharging (especially 9V batteries). Why does this happen, and is this normal?
A. Some heat during charging is normal and some chargers work faster than others. If you have doubts, you should stop and check that the battery is right for the charger AND that it isn't swelling.
Any Swollen batteries are potential danger and should be discarded.
Q. I have a set of 4 AA rechargeable batteries (relatively new), where one of them loses its charge very quickly. The other three work OK. What is going on?
A. Ideally each and every cell should be charged alone, but many chargers work in pairs or other groups. If one battery is weak or defective, the charger merely responds by attempting to charge the group and the 'runt' looses out. In some cases, switching the batteries around helps. In some cases, you just have to accept that you got a bad battery - take it back and ask for a replacement.
Q. Where does one buy Lithium Polymer rechargeable batteries? I only know about them being used in notebook computers. Are they available in the standard AA, AAA, 9V sizes?
A. Physical chemistry creates the actual Voltage in a battery. Tradional flashlite batteries were all 1.5V, so many people think every battery should be like that. NiMh and NiCA are 1.2V. Lithium Ion batteries are in mutiples of 3.7volts. Since that have much higher energy density, when built as a sealed battery they have a greater ability to burst.
While there are some Lithium batteries shaped like conventional batteries, they won't simply replace an AA or a C cell. You can buy Lithium batteries and chargers at electronics supply house and R/C hobby stores.
Since there is a greater chance of bursting, a good Lithium charger is quite important. And since over-heating appears to quickly destroy the Lithium Polymer beyond recharge ability, the better chargers have thermal shut down.
In some cases, you will see Lithium batteries with their own 'thermal shut-down' and 'low-power' shut down. These actually have a circuit board attached and may explain why you see them rated at less than the 3.7volts.
Q. I would like to make a recharger that I could put on a small robot (like the BOE-Bot). Could anyone tell me how to make one, or point me to any schematics and/or instructions? I opened my store-bought recharger and it looks like it's just a wall-wart DC adapter connected to a resistor that then connects to the battery terminals. Is it the wall-wart that prevents the batteries from discharging? How does the recharger know when the recharging is completed (or, how do I make it shut off when it's done)?
A. Rechargers are getting more complicated everyday. Generally, I would strongly recommend you buy a Lithium Ion charger rather than make one as it is likely to be both cheaper and safer to do so and provide you better value.
Regarding the other types, Google for schematics.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 3/26/2006 3:41:52 PM GMT
Very useful information!
an old cam-corder, into a rechargeable supply for the BOE.. I took a 5-cell Sub-AA
pack (2/3-height AA's,) and changed the OOOOO into a .....
O O
O O O -like stack. Took a couple of twist-ties (Ala-VEX, Sorry..), and mounted
it in place where the old battery pack used to be. So-far, brief use, the batteries haven't
been charged in 5 weeks! (brief use meaning 10-12 minute runs per week.) and they're
still full power.
Only drawback, the pack is so low in the frame, it only clears the rear ball-wheel by 1/4" , and the
ground by 1/2".
I haven't figured on how to make the BOE search-out a charger, but an interesting idea.
Stephen
Just saying this to help people who have the same question.··· -SciTech02.
The other two are 6volt 1Amp hour Gel cells. These little Gel cells are really useless. NiMh has more capacity, less weight and fits in battery holders. I may use them as 'backup power' but they were a complete waste of money.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan