Hi,
I didn't know where to put this but a charger is solid state electronics so move the thread if it is not apropriate here. I'm building my electric bicycle based on a 48 volt system and now realised that charging each batteries one at a time at 12 volt is alot of hassle. I want to build a 48volt one, but all the current sensing chips to switch the charging in trickle mode I can find are made for 12 or 24 volts. Does anyone know of one that can do 48 volts?
Thanks for any help!
I didn't know where to put this but a charger is solid state electronics so move the thread if it is not apropriate here. I'm building my electric bicycle based on a 48 volt system and now realised that charging each batteries one at a time at 12 volt is alot of hassle. I want to build a 48volt one, but all the current sensing chips to switch the charging in trickle mode I can find are made for 12 or 24 volts. Does anyone know of one that can do 48 volts?
Thanks for any help!
Are you sure? All electric bike or scooters have their batteries in series (2x12, 3x12 or 4x12) and are charged with the same voltage charger. I found some selling but they are made to charge the batteries from electric golfcarts so their current is way to high. All I need is about 2 amps nothing more.
There's no problems charging batteries in series if they are all the same type, size, age, specific gravity, etc.(matched set that are always in series when charged and discharged. An occational long term slow trickle charge is good to top off all cells.
If the circut you plan to use senses current (in series with battery), then the voltage will not matter. If it senses voltage, then a voltage divider network could scale the voltage by 2 or 4.
All battery packs greater than 2 volts (except lithium) are cells in series. (12v cordless tools use 10 1.2v nicads or NMH... auto batteries are 6 cells 2v lead/sulfuric acid etc.)
If the circut you plan to use senses current (in series with battery), then the voltage will not matter. If it senses voltage, then a voltage divider network could scale the voltage by 2 or 4.
All battery packs greater than 2 volts (except lithium) are cells in series. (12v cordless tools use 10 1.2v nicads or NMH... auto batteries are 6 cells 2v lead/sulfuric acid etc.)
You don't really need to switch over to trickle charge mode as such. Presuming you are using sealed lead-acid batteries, just make yourself a supply that puts out 54.6 volts (=13.65 volts per 12v batt) with a 2 amp charging current limit. The batteries will draw 2 amps on charge until their voltage rises to 54.6 total and then the current will gradually reduce to an eventual low trickle value while the voltage remains at 54.6 for as long as you like with no problem. e.g. years. An even better way would be to charge each 12v block separately but at the same time, using 4 chargesr(!) This would help to ensure that each cell in the string would get an equal voltage and therefore charge. The longer the string of cells the more likely they will get unbalanced over a period of time.
/Circlotron - mucks around at work with telephone exchange type battery chargers. 54.6 volt, 585 amps rack mounted switchmode.
/Circlotron - mucks around at work with telephone exchange type battery chargers. 54.6 volt, 585 amps rack mounted switchmode.
What type of barreries do you plan to use. Different ones need different types of voltage or current regulation. Circlotron's comments are a great for lead acid batteries and would be quite simple. Nicads are different. I think they are best charged in short high current pulses. This is not so simple. They can be trickle charged, but don't overcharge. If you know the ampehour rating, you can do the math. 1.2 amp hour battery will nned to slow charge at 120 ma for 10 hours (for ideal battery) to 10.5 hours(real battery)
Well, automobiles have used alternators which hold the battery at a somewhat constant voltage. If you were to do as suggested and make one to apply about 13.5 volts per battery in series with occasional trickle charges to even out the charge on each of the 24 individual cells, then you should be OK.
You may consider using a SMPS circuit for compactness. Then you can consider building the charger onto the bicycle. You may be able to base it on my circuit which is described at
http://groups.yahoo.com/group/switchmode
You may consider using a SMPS circuit for compactness. Then you can consider building the charger onto the bicycle. You may be able to base it on my circuit which is described at
http://groups.yahoo.com/group/switchmode
Well it is not that simple. With lead acid batteries the trickle voltage depends of their use. Is it cyclic use or is it standby use. For standby use a trickle voltage of 2.35V/cell is recommended, for cyclic use 2.45V/cell is recommended. So the best and fastest way is to charge with 2.45V current limited to app. 0.3x Ah value. When the charging current drops to 5% of the Ah value switch over to 2.35V to trickle charge. Besides this, the voltages are also slightly temperature dependent. Sensing current can be done with a resistor in the ground lead of the batteries. But the perfect solution is a compensated current transformer from LEM. These will measure DC and are not that expensive, around $10. For instance the LTS-NP25 (PDF at http://www.lem.com/ ).
But for your bicycle a fixed voltage of 2.45V/cel will suffice. Provided you do not leave it at the charger for days.
More important with lead acid batteries: Do not leave them partially discharged for extended periods and do not discharge them fully. This will greatly reduce their life. After each use recharge them as soon as possible.
But for your bicycle a fixed voltage of 2.45V/cel will suffice. Provided you do not leave it at the charger for days.
More important with lead acid batteries: Do not leave them partially discharged for extended periods and do not discharge them fully. This will greatly reduce their life. After each use recharge them as soon as possible.
yes it will be used in cyclic use. I try not to fully disharge and when I do not use them during the winter I recharge them at about each 2 months just to keep them charged. Ok, I already know that I need 2 amps but what voltage? I am very confused lol! Each batteries have 6 cells of 2 volts needing 2.45 volts to recharge. So I need a 58.8volts 2 amp power supply? I want to do a smps as subwo1 suggested to reduce size and implement it directly to the bike.
Thank you very much for all the replys!
Thank you very much for all the replys!
You should do OK just by contructing a charger with a voltage of 58 volts like you were thinking. You do not really have to worry about the current very much because the amount of current is limited by the charge voltage. But with the switching power supply design like mine, you can chose the level at which current limiting kicks in by changing the value of C13.
http://groups.yahoo.com/group/switchmode/
You will probably want D3 to be something like a 48 volt zener or something thereabouts. You would also need to add an adjuster rheostat in series with R3.
http://groups.yahoo.com/group/switchmode/
You will probably want D3 to be something like a 48 volt zener or something thereabouts. You would also need to add an adjuster rheostat in series with R3.
Brian Donaldson
I have a case of 12V/7Ah SLA batteries that I want to keep charged with a Schauer 12V/10A automatic charger presumably designed for larger batteries. The technotes on the charger say that it isn't recommended for these smaller 12V/7Ah cells but I was wondering if I could recharge 8 or even ten cells at once by connecting all the + terminals together to the + on the charger and all the - terminals to the - on the charger in order to reduce the current inrush. If I do this, will I damage the cell or the charger?
Sounds feasible.Your charger is probably 10 A limited and you wouldn't want charge small batteries with that much.However with 10 in parallel that would work out to 1A each.
But how would you then connect them to your power amp?(assuming that's what you are going to use them for) unless you rewire every time.
But how would you then connect them to your power amp?(assuming that's what you are going to use them for) unless you rewire every time.
The ten cells would have their - posts connected to a common rail and the + posts connected to another common rail and these would terminate externally on the case as two insulated posts (one for each rail). I don't know exactly how this automatic charger works but if we go by the formula posted earlier in this thread it looks like this scheme would charge a bit too fast.
Here is what I gathered from my readings:
12V/7.2Ah safe charge requires 12 hours @ 600mA
If we multiply this by 10 cells we get an ideal charge with 12 hours @6A. The 10A charger may force too much current and damage the cells. The other problem is how the cells will accept the charge according to the layout. What happens if some of the cells charge more quickly than the others? What exactly happens to the cell if it is charged too quickly? What will an automatic charger do when some of the cells are topped off and the remaining still need charging? Do the remaining cells divide the full current when the topped cells accept no more charge?
Here is what I gathered from my readings:
12V/7.2Ah safe charge requires 12 hours @ 600mA
If we multiply this by 10 cells we get an ideal charge with 12 hours @6A. The 10A charger may force too much current and damage the cells. The other problem is how the cells will accept the charge according to the layout. What happens if some of the cells charge more quickly than the others? What exactly happens to the cell if it is charged too quickly? What will an automatic charger do when some of the cells are topped off and the remaining still need charging? Do the remaining cells divide the full current when the topped cells accept no more charge?
Yes parallelling batteries is dangerous buisness. It can only be done if the batteries are identical and new and remain a continuous set.
Charging at 10 A wounldn't be catastrophic, and If it's a automatic charger, the current is usually less than the stated rating. They usually rate them as maximum charge rate with a bone dead battery. Watch the current meter, or if it doesn't have one, wire yourself an amp meter in series with charger and see what the current is.
Charging at 10 A wounldn't be catastrophic, and If it's a automatic charger, the current is usually less than the stated rating. They usually rate them as maximum charge rate with a bone dead battery. Watch the current meter, or if it doesn't have one, wire yourself an amp meter in series with charger and see what the current is.
Brian Donaldson
Yes, the charger does indeed have a current meter. Below is a table of the measured voltages on the cells:
1-12.72
4-12.62
3-12.61
1-12.60
1-12.59
The batteries all come from the same case/lot and only the top one has gone through a one time recharge (a 30 second jolt at the full ten amps) just to see what would happen. I disconnected when the meter on the charger hit 7A. Which battery should go first in the cue or doesn't this matter since all the cells are on the same charging rail? How much am I likely to shorten the life of these batteries by charging at a 50% higher than recommended rate?
Yes, the charger does indeed have a current meter. Below is a table of the measured voltages on the cells:
1-12.72
4-12.62
3-12.61
1-12.60
1-12.59
The batteries all come from the same case/lot and only the top one has gone through a one time recharge (a 30 second jolt at the full ten amps) just to see what would happen. I disconnected when the meter on the charger hit 7A. Which battery should go first in the cue or doesn't this matter since all the cells are on the same charging rail? How much am I likely to shorten the life of these batteries by charging at a 50% higher than recommended rate?
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