# making a 'semi-smart' single cell charger....



## gdirwin (Apr 7, 2009)

Check out mastechpowersupplies.com... I bought one of the lower volt/higher amp models for my initial balance and charge...


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## dtbaker (Jan 5, 2008)

gdirwin said:


> Check out mastechpowersupplies.com... I bought one of the lower volt/higher amp models for my initial balance and charge...


thats what I use right now.... the 10amp model was only $149 or so, but if set to CC max there is no auto-cutoff so you can't just walk away or it would go overvoltage, and 10amps is just too slow anyway. If set to 3.80v CV, I might see 5 or 6 amps in the beginning, but it obviously drops as it goes and still doesn't have an auto-off so I have to keep checking in on it and it can take a LONG time per cell for amps to drop to some consistent small value before manually stopping the charge.

I want something that will pump in 20-40 amps, hit 3.70v, and turn itself off.


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## frodus (Apr 12, 2008)

Lightobject's JLD404 has alarms, just use the relay on it to enable/disable your power supply.
http://www.lightobject.com/Programmable-Digital-AH-meter-Ideal-for-battery-monitoring-P278.aspx

You don't technically need that model, I'm sure just one of their Voltage sense devices would work, since you're not measuring amps or watts.... but it could be nice to know how much energy you put in the cell.

Something like this (has alarms):
http://www.lightobject.com/Programm...th-dual-control-Good-for-HHO-System-P408.aspx


People use them for bottom balancing, but they can also be used for HVC, rather than LVC. It's just a setpoint that the alarm triggers at. I have a JLD404 and I use it for charge/discharge control.


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## Ziggythewiz (May 16, 2010)

The 404's cool because you can see how much is going into each cell and reliably predict when it will be done if you want to be there when it completes.


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## frodus (Apr 12, 2008)

The relays are rated for low amps, so use that + power supply to drive a larger relay/contactor.


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## ga2500ev (Apr 20, 2008)

Dan,

Your monitoring needs screams microcontroller. With ADC, PWM, and comparitors a part like a Microchip 16F1XXX or 18F part can be used for control.

ga2500ev


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## Elithion (Oct 6, 2009)

dtbaker said:


> I have found some straight power supplies


Regulated power supply != Charger

A power supply will operate at a constant voltage, not at a constant current. If you connect it to a cell or battery that has a lower voltage than what it's rated for, it will balk: shut down, cycle off and on, overheat or maybe even blow up.

(A "lab supply" can work as a charger, because it has a constant current mode.)




dtbaker said:


> My question is what would I have to add to monitor the voltage


Just set the supply to 3.60 V, and the current will naturally taper off to 0. That's it. Even better, do 3.4 V, and you don't have to worry about keeping the cell at 3.6 V for a long time. See this tip on pre-balancing cells.


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## PStechPaul (May 1, 2012)

You can start with a 5V 60A switching supply for about $65. Sometimes you can find bigger ones. I have a 5V 200A supply I bought for $20 or so at an electronic flea market (Hamfest). It is possible to parallel supplies to get more current, especially if you use steering diodes (but they will drop about 1V (or 0.5V for Schottky) so 30-60W at 60A. 
http://www.mpja.com/5-Volt-Power-Supply-60A-300W-Switching-Hengfu/productinfo/16486+PS/

Then you just need to have a way to control the current and peak voltage. A PWM control is efficient and easy with a microcontroller and a big MOSFET or IGBT, especially with a series inductor to smooth the current. Or you could just make a linear regulator which would drop about 5-3=2V at 60A or 120W. The power supply might also be adjustable to a lower voltage.

From my limited experience with lithium cells I found that they will reach their target maximum charge voltage fairly quickly at maximum current but you can reduce current and charge more. I used a Li-Ion 3600 mAh 3.7V cell and it only accepted about 1000 mAh up to 4.2V, but it's a cheap cell and it may have been able to accept a bit more if I had reduced the current, but it reached the maximum at about 250mA.

Using a PIC it would be easy to monitor both voltage and current and provide the charging profile you want. It could taper the charge at the end and shut off the power supply using a SSR on the AC line, and perhaps signal an audible or visual alarm.

I need to build this myself. I already have most of what I need in my datalogger which has the advantage of transmitting the charge (or discharge) data to the computer via a serial/USB port, and it also could respond to commands from the computer. The electronics (PIC, op-amps, RS-232 IC, etc) are no more than about $20 or so, especially if using surplus parts for the power section (MOSFETs and IGBTs fro eBay).

You can also get digital process meter/controllers which can be set up with setpoints that trigger an alarm and/or shut off a power supply at a specific voltage and/or current. Like this:
http://www.omegadyne.com/ppt/prod.html?ref=DP41
http://www.ebay.com/itm/OMEGA-digit...961?pt=LH_DefaultDomain_0&hash=item4cf3baeb79 ($139)
or this:
http://www.ebay.com/itm/Newport-INF...ess-Panel-Meter-Controller-Unit-/150987646830


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## rmay635703 (Oct 23, 2008)

Guys Many PC power supplies have trim pots, I have several that can be tuned down into the 3.x range on the powerfull 5v rail, I have also found many 5v lab powersupplies have trim, so the regulation may already be in the PSU.

Since a PC supply cuts out if you overload you can either oversized the crap out of it or put a resistor on the output to limit it to a reasonable value and the charge will just do a nice curve.

CHeers
Ryan


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## PStechPaul (May 1, 2012)

If you can adjust the 5V supply down to 4V you can just add a series diode to get about 3-3.5V maximum. A diode may be ideal because it has a higher voltage drop at higher currents so it will taper off the charge as the voltage nears the theoretical junction voltage. It also has a lower voltage drop at higher temperature which may be ideal to reduce the charge when the cells are cold. It is probably not a good idea to run the power supply to its limit, though, as many of them have foldback current limiting.

If the power supply has remote voltage sensing you can build a little 100x amplifier and read the voltage on a 50mV 50A shunt to regulate the output at 50A.


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## gdirwin (Apr 7, 2009)

dtbaker said:


> thats what I use right now.... the 10amp model was only $149 or so, but if set to CC max there is no auto-cutoff so you can't just walk away or it would go overvoltage, and 10amps is just too slow anyway. If set to 3.80v CV, I might see 5 or 6 amps in the beginning, but it obviously drops as it goes and still doesn't have an auto-off so I have to keep checking in on it and it can take a LONG time per cell for amps to drop to some consistent small value before manually stopping the charge.
> 
> I want something that will pump in 20-40 amps, hit 3.70v, and turn itself off.


Hi Dan:
Mastech 20A models are about $210, and a 50A model is $420.

I am confused with your above setup - why is the current only 5 or 6 amps instead of 10? It appears there is a very large internal resistance somewhere (thin wires?). 

With the charge cables disconnected you should set the voltage knob to your CV voltage setting, then with the wires connected set the CC know to its max - you should get 10Amps until the voltage (at the power supply terminals) hits the CV setpoint - then the current should taper off until it is fully charged...

Garth


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## frodus (Apr 12, 2008)

In order to get current to flow, you must have a voltage differential. The greater that differential, the more current flows.

With power supplies, they're dumb, and they just try get the voltage to the setpoint... lets say 3.7V on Lifepo4 cells. Lets say the battery is at 3.5V and climbing. That's only 0.2V differential, so it may not pull much current. Power supplies don't FORCE current into the battery.

So to pull more amps, you need to try to pull the voltage higher, therefore causing a higher current flow. Then, as the battery reaches the voltage setpoint adjust the voltage back down, and let the current start to fall.

So the issue really is, that these chargers aren't very smart. When you just set a voltage and wait for it to get there, you won't pull many amps. It may pull max amps at the beginning, when the voltage differential between the battery and charger is greater.


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## gdirwin (Apr 7, 2009)

Yes, but it still doesn't add up... The voltage differential is small (say the flat part of battery VI curve is about 3.5V and the CV cutoff is 3.8, so differential is 0.3V) - at 10 amps this could only occur if the total internal resistance was 30 mohms. The cell internal R is less than 1 mohm, so either very long or small diameter charging cables were used (ie high resistance)...

Ie CC should be possible up to the knee point of the VI curve, which is nearly all of the charging energy/time...

Were the charge cables small diameter or really long?


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## dtbaker (Jan 5, 2008)

frodus said:


> In order to get current to flow, you must have a voltage differential. The greater that differential, the more current flows.
> 
> With power supplies, they're dumb,



thats the problem in a nutshell. A higher capacity regular bench power supply does me little good because it cannot automatically dial the voltage up to obtain max current, monitor, switch to CV when target is hit, and turn itself off..... thats what a CCCV charger does, or at least should do.

I am willing to go with 'semi-smart' and stop after the CC, when target voltage is hit, and auto-off... but don't have the electrical knowhow to design whatever it is to monitor voltage and stop the charge accurately and reliably if I start with a dumb fixed voltage (cheap) power supply. 

soooo..... 
first question is, what voltage would a dumb fixed voltage power supply have to put out to have enough differential to a cell sitting at 3.3v to create a 50 amp current charge? 12v? 24v?

let's say I can find a 'fixed' power supply that can crank out 50 amps at 24 volts, hopefully for around $100. given that the supply is 24v, that should be enough differential to enable max current to the cell; obviously can't walk away unattended though. 

what do I need to add to monitor cell voltage and stop the charge automatically and shut down the unit when cell hits 3.70 volts (accurately and reliably)?


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## PStechPaul (May 1, 2012)

You can use a 5V or 6V supply and a resistor to limit current to your maximum of 50 amps into a 3.2V cell. A 0.04 ohm 100W resistor will do it for 5V, with a difference of 5-3.2 = 1.8V/0.04 = 45A. The current will taper down to 5-3.7 = 1.3/0.04 = 32.5A. You can use a meter relay to turn off the power supply at the setpoint you choose, in this case 3.70V. 

Use 8 of these for 0.04 ohm 80W ($0.64 ea):
http://www.mouser.com/ProductDetail...GAEpiMZZMtTURnxoZnJAGPwGBE7IkPIgMou0Yt%2brUE=

Here is a meter relay that should do the job for $30:
http://www.ebay.com/itm/METER-RELAY...t=BI_Control_Systems_PLCs&hash=item4abb8e099d

Actually I have one of them you can have for $20 plus shipping.

This should also work ($12):
http://www.ebay.com/itm/DC12v-relay...ltmeter-detection-control-meter-/290788924156

You might also be able to use one of the Mini-BMS modules:
http://www.cleanpowerauto.com/MiniBMS.html


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## dtbaker (Jan 5, 2008)

PStechPaul said:


> You can use a 5V or 6V supply and a resistor to limit current to your maximum of 50 amps into a 3.2V cell. A 0.04 ohm 100W resistor will do it for 5V, with a difference of 5-3.2 = 1.8V/0.04 = 45A. The current will taper down to 5-3.7 = 1.3/0.04 = 32.5A. You can use a meter relay to turn off the power supply at the setpoint you choose, in this case 3.70V.
> 
> Use 8 of these for 0.04 ohm 80W ($0.64 ea):
> http://www.mouser.com/ProductDetail/Xicon/280-CR10-033-RC/?qs=sGAEpiMZZMtTURnxoZnJAGPwGBE7IkPIgMou0Yt%252brUE%3d
> ...



ok, I'm liking details, but not sure of a couple things. first, it seems like with my variable power supply, the only way I get it to put thru its max 10 amps to a cell is if I crank the voltage well above 6 volts... basically up closer to its max 30v. so, my question becomes exactly HOW do I use a 0.04 ohm 100W resistor to get a 6v power supply to jam 50 amps into a cell? 

Wouldn't it be easier to look for a 12v or 24v power supply that has an internally limited max output of 50 amps or so and just let it rip at its 12v or 24v to ensure max current? Can anyone suggest an inexpensive power supply, fixed voltage fine, with 40 or 50amp max current?


the second part of the issue.... the meter-relay to watch cell voltage and end the charge....I looked at the first ebay link, and don't see how that would do the job at all. 

The second one looked closer, but the specs show it needs 10-15vDC for power, so I guess it would require an external ac-12vDC adaptor plug? not a problem. but then I wasn't sure the relay side could handle turning the vAC off to the main power supply? I guess it could since it looks like the relay label read 10A-250VAC. what' throwing me on this one is I can't tell if it is designed to open the relay when voltage RISES to setpoint, or FALLS to setpoint? ...but does give hope that a little relay won't be too expensive, and may well be fine to turn off a power supply when limit is hit.


would something like this
http://www.ebay.com/itm/600W-DC-12V...098?pt=LH_DefaultDomain_0&hash=item51a398ffa2

be a suitable power supply? $60-$70 plus $30 shipping from china/hong kong. Looks like all I need is one of these and a little volt sense/relay to turn it off when cell voltage rises to setpoint voltage?

anybody else wanna comment? have any better little pieces to suggest?


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## PStechPaul (May 1, 2012)

You don't want a 12V or higher supply for a single cell. The reason you can't get the current you want is because of too much resistance in the circuit. You could force more current through that resistance using 12V, but you would be dropping about 9V at 50A or 450 watts. That would probably melt the leads or burn up whatever is causing the excessive resistance. You need to fix that before proceeding any further.

When you take care of that (by using at least #8 AWG leads and solid bolted connections to the cell and power supply), you can look at a more suitable PSU, such as:

http://www.ebay.com/itm/SCC-STATIC-...50A-DC-POWER-SUPPLY-920-PS-5-50-/221059394810
$27.50 + $15 shipping

http://www.ebay.com/itm/Mean-Well-M...verter-SD-50A-5-9V-18V-Input-CE-/350619638013
$38.72 free shipping (this is a DC-DC converter if you want to use a 12VDC battery to get 5V for charging)

http://www.ebay.com/itm/5V-50A-360W-DC-Regulated-Switching-Power-Supply-CNC-/140726113423
$39.99 + $5 shipping

You should measure the voltages at your power supply and across the battery, and from end to end of your leads, to see where the excess voltage drop is happening.

As for the meter relay, usually a single setpoint type triggers a relay when the meter reads higher than the setpoint. And you may need to adjust the voltage of the meter relay for what you need, which is 0-5 VDC. That involves using a scaling resistor for a 0-1mA meter movement (which is 1000 ohms per volt). So for 5VDC you need 5000 ohms. 

The contacts are usually SPDT so you can choose whichever works to open at the high setpoint. But you also need a way to keep the supply turned off after it reaches the setpoint, because otherwise the voltage will drop and the supply will cycle ON/OFF. So you need a latching relay and a momentary pushbutton to energize it. Here is the basic circuit from http://www.allaboutcircuits.com/worksheets/latch.html:









You just put the meter relay contacts in place of the stop switch. You have to tap the Start button to energize CR1 (Control Relay), which energizes the motor (in your case, the power supply), and the coil of CR1 is kept on by the other NO contact. When the meter relay contacts open (like the Stop switch), both contacts of CR1 open and the circuit is deenergized.

If you watch the video of the MiniBMS you will see how it turns off the charger at the high voltage cutoff point and keeps it off until the circuit is reset. You can get one of those units for about $12 and an SSR as shown, and you're almost done. But his units are preset to 3.6V or 3.8V, so you may need to modify it if you need 3.7V. BTW, it is very important to measure the voltage directly on the terminals of the cell, especially when using a high charge rate and connections which may have significant resistance, as these will result in a higher voltage and premature cut-off.


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## dtbaker (Jan 5, 2008)

PStechPaul said:


> You don't want a 12V or higher supply for a single cell. The reason you can't get the current you want is because of too much resistance in the circuit.


this I am not understanding. The LiFePO4 cells have very low resistance, the leads are plenty big, I don't think resistance is limiting the charge current when I use my Mastech 0-30v, 0-10a power supply.... I think its just that it cannot push more than 10amps regardless of the voltage differential.

In my mind I just need a big enough voltage differential to ensure the power supply tries to pump thru all it can, and get one that can put out 40-50amps would be great. I see the CC rating of the supply as being the limiting factor as long as there is enough voltage differential. Am I missing the boat on this?




PStechPaul said:


> http://www.ebay.com/itm/SCC-STATIC-...50A-DC-POWER-SUPPLY-920-PS-5-50-/221059394810
> $27.50 + $15 shipping


I just don't think a 5v power supply will have enough differential to hit 40-50amps, but I'm just going by what I see when I diddle with the knobs on me adjustable power supply. I don't get why I wouldn't be better off with a 12v-50amp PSU to be sure to crank up the current to the cell?



PStechPaul said:


> If you watch the video of the MiniBMS you will see how it turns off the charger at the high voltage cutoff point and keeps it off until the circuit is reset. You can get one of those units for about $12 and an SSR as shown, and you're almost done. But his units are preset to 3.6V or 3.8V, so you may need to modify it if you need 3.7V.


3.6, or 3.8 would be fine.... the absolute value for occasional balancing is not as critical as the repeatability cell to cell.


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## PStechPaul (May 1, 2012)

Does the Mastech variable supply give you 10 amps when you set the voltage to 12V? Check the lights on the supply to see if it is in current limit or voltage limit. I have found that the Mastech supplies do not work really well on current limit, and they do not put out quite what they are rated for. I have a HY3006D (30V 6A), and it won't put out much over 25V or 5A. If you have a solid 5VDC and good leads and connections, you should get all the current you need. 

I think the power supply is having problems driving the battery load, and it may work better if you add some series resistance. You can use a length of steel coat hanger wire as a low resistance if you don't have a resistor.


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## dtbaker (Jan 5, 2008)

PStechPaul said:


> Does the Mastech variable supply give you 10 amps when you set the voltage to 12V? Check the lights on the supply to see if it is in current limit or voltage limit.


I won't have a chance to mess with it till the weekend probably. I'll see if I can pin down what voltage it takes to peg the current at its 'max' 10a... I do remember as I raised the voltage, there was a point for sure where the amps pegged at 10, and the light indicators flipped from CV to CC side.

what I really want to know is what the voltage would have to be to peg at 40amps or 50amps if the PSU could go that high......


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## dimitri (May 16, 2008)

The idea is to use cheap and widely available switching power supplies, but they are CV devices and rated for passive loads. They act differently when used as a charger, since potential difference is too small to produce max rated current. Supply simply holds its CV level as sensed at the output terminals of the supply, but it cannot account for voltage drop between supply and the cell terminals. So, you need to provide best possible connection to reduce voltage drop and gain max current, which will be about 1/3 of rated current in my experience if you use CV under 4.0V safe for LiFePO4 without any extra monitoring/management.

Here is my rig, its a 3.3V supply, which can be dialed up to 3.85V-3.9V using trimpot next to the LED. This way I don't need to mess with monitoring and can just walk away without risk of overcharge. Downside is that I get average of 10 Amp, even though supply is rated for 30 A. I say average because it starts higher as cell voltage is lower and drops to nothing as cell voltage climbs up. I have average drop of 0.5V between supply and the cell, using 10 AWG jump start cable, which I cut in half and attached to the supply. Heavier and shorter cable would give less drop and more current, but I am too lazy to change it.

If I needed even more current, I would buy 5V supply and attach single miniBMS board wired with SSR relay on AC side of the supply, such that BMS board cuts off SSR and stops the supply. It adds complexity since you need a head board to make HVC action latching off and it needs its own 12V power. Without head board you can wire SSR thru the cell board and feed it off the cell itself, but it will be bouncing on/off at the end. Depending on how well the rig is watched, it could be a very simple and cheap solution.

With 5V supply you'd be wasting more energy in heat and you might need to play with connection wires to manage voltage drop such that you don't overload the supply at peak current.

Of course these are all simple and cheap solutions. If you want more complexity, build a PWM rig with Arduino so you can turn a CV supply into a CC/CV one.


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## dimitri (May 16, 2008)

dtbaker said:


> what I really want to know is what the voltage would have to be to peg at 40amps or 50amps if the PSU could go that high......


the answer to this question depends on connections between supply and the cell and will vary widely. 

also, that voltage will surely be above 4V at the supply side, which means you cannot leave this rig unattended unless you have automatic cutoff which is sensing at the cell terminals

the key in dealing with CV supplies as chargers is to understand WHERE you are measuring voltages, at supply or at the cell


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## dimitri (May 16, 2008)

Here is what I would get if I wanted 5V supply, it can be dialed between 4.5-6.0V so you have some control of peak currents by adjusting CV level.

http://www.digikey.com/product-detail/en/SWS3005/285-1622-ND/1631789

Here is the 3.3V one I use, the same one in my photo

http://www.digikey.com/product-detail/en/LS150-3.3/285-1814-ND/1918825


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## dimitri (May 16, 2008)

This one is interesting, unfortunately out of stock at Digikey, maybe available somewhere else.

It has remote voltage sensing feature, so if you dialed it to say 3.6V and attached remote sensing wires at the cell, then it would try to maintain 3.6V at the cell, essentially ignoring voltage drop on main connection wires.

Of course we don't know how high it will push voltage/current trying to maintain CV at the cell, so it would be an experiment if someone wants to try it and share results.


http://www.digikey.com/product-detail/en/SWS600L-3/285-1789-ND/1918801


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## dtbaker (Jan 5, 2008)

dimitri said:


> also, that voltage will surely be above 4V at the supply side, which means you cannot leave this rig unattended unless you have automatic cutoff which is sensing at the cell terminals
> 
> the key in dealing with CV supplies as chargers is to understand WHERE you are measuring voltages, at supply or at the cell


exactly... I keep circling back to this, I guess I'm not explaining myself well. I KNOW I need more than 5v at the supply side to be ABLE to push 40-50 amps into a cell. The fixed voltage power supplies are pretty cheap, so my question is IF I have big fat jumper cables and almost no voltage drop between supply side and cell terminals, what voltage do I need at supply to push 40-50 amps into the typical LiFePO4 prismatic cell? 6v? 12v? 24v?

I pick the 40-50amps on cell side because I want to use a regular household 110v outlet at no more than 12 amps.... so somewhere between 500-1000 watts thru to the cell would be the best reasonable goal.


second question is how best to accurately and dependably turn the power supply off, and stay off, as soon as the cell terminals hit target voltage (like 3.60-3.80). 

I am looking for a repeatable charge to top-balance as quickly as possible. Something I can move from cell to cell, go do something else for a couple minutes, come back and move to the next cell... If I can basically charge in CC and pump in 500-1000watts, and have the unit auto-off when it hits set voltage it should only take a couple minutes per cell.


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## Ziggythewiz (May 16, 2010)

dtbaker said:


> exactly... I keep circling back to this, I guess I'm not explaining myself well. I KNOW I need more than 5v at the supply side to be ABLE to push 40-50 amps into a cell. The fixed voltage power supplies are pretty cheap, so my question is IF I have big fat jumper cables and almost no voltage drop between supply side and cell terminals, what voltage do I need at supply to push 40-50 amps into the typical LiFePO4 prismatic cell? 6v? 12v? 24v?


I don't think you need that high of a voltage at all. The important thing is the supply being able to deliver enough current, and exact resistances of the cells. I've seen my booster pack charge at up to 20A from a supply equivalent to under 3.2 vpc.

According to elithion's data a CALB cell has a resistace of 1.27 mOhm, so you'd really only need a voltage difference of .05 to drive 40A if your cables and charger had no resistance. Obviously they don't, so that will be a big part (possibly most) of the equation, but it still won't be as high as 5V if the power supply can handle that much power at all. 

However, the apparent IR of the cells change greatly over the course of a charge so the voltage has to compensate to maintain CC.

I think you have to have a microprocessor (and a capable power supply) to do CC.




dtbaker said:


> second question is how best to accurately and dependably turn the power supply off, and stay off, as soon as the cell terminals hit target voltage (like 3.60-3.80).


A JLD404 can do that, and tell you exactly how much power it took to get there. Just set the low trigger to the desired high and the high trigger to your cell's nominal voltage.

A programmable state relay would be better IMO, but I'm not aware of any (haven't looked).


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## PStechPaul (May 1, 2012)

I don't have direct experience with large prismatic lithium cells, so perhaps I am mistaken, but the internal resistance of a 100 Ah cell should be no more than a few milliohms. You should be able to get at least 5C (500A) with maybe 10% droop, or 0.32V/3.2V, or 0.32/500 = 0.64 milliohm. Even a 10 Ah cell would be maybe 6 milliohms. So to put 50 amps into the cell, the external voltage should be higher than the basic 3.2V cell voltage by 50*0.006 or 0.3V higher, or 3.5V worst case. If you can't get 50 amps at 5 volts it means your cell resistance is higher than (5-3.2)/50 = 0.036 ohms. 

There is no reason to require a 12V or 24V supply. Think about it. 24 volts at 50 amps is 1200 watts. Subtract the maximum cell voltage (3.6V) and there will still be over 1000 watts of heating somewhere. If it's not in the cables to the cell, then it's in the cell. And that's enough power to burn it up very quickly. Maybe you have a bad cell? It might have a very high internal resistance if it is totally depleted (and damaged), and it might only accept a small amount of current at first, but if it returns to anything close to normal, the resistance will drop and you will get a very high current unless the supply is limited.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> I don't think you need that high of a voltage at all. The important thing is the supply being able to deliver enough current, and exact resistances of the cells. I've seen my booster pack charge at up to 20A from a supply equivalent to under 3.2 vpc.


how would you get ANY charge if the supply voltage is lower than the cell?




Ziggythewiz said:


> A JLD404 can do that, and tell you exactly how much power it took to get there. Just set the low trigger to the desired high and the high trigger to your cell's nominal voltage.


I don't think so.... specs show the jld404 relays are rated for 3 amp.... the powersupply would be chugging along at 10+amps . besides a jld404 is close to $100 when it looks like a little half-brained voltmeter/relay board is only around $12. Issue there is the chinese documentation....


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## Ziggythewiz (May 16, 2010)

dtbaker said:


> how would you get ANY charge if the supply voltage is lower than the cell?


3.2V is nominal, not full, so if they are ~20-30% SOC they'll be less than that and charging from a 3.2V source. 



dtbaker said:


> I don't think so.... specs show the jld404 relays are rated for 3 amp.... the powersupply would be chugging along at 10+amps . besides a jld404 is close to $100 when it looks like a little half-brained voltmeter/relay board is only around $12. Issue there is the chinese documentation....


Yes, you'd have to use the onboard relay to drive an external one. 

Of course there are cheaper options. It was just an example. 

I used a JLD404 to top balance my cells and then stuck in the the car, so not an additional expense.


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## frodus (Apr 12, 2008)

frodus said:


> Lightobject's JLD404 has alarms, just use the relay on it to enable/disable your power supply.
> http://www.lightobject.com/Programmable-Digital-AH-meter-Ideal-for-battery-monitoring-P278.aspx
> 
> You don't technically need that model, I'm sure just one of their Voltage sense devices would work, since you're not measuring amps or watts.... but it could be nice to know how much energy you put in the cell.
> ...


Reposting this. There are other models that are ONLY voltage, and much cheaper. Yes you'll need a relay that the JLD can handle, as well as a 12-24V power supply. I just don't know how much cheaper you're wanting to go, or what you expect. This gives you a readout, alarms that you can set and relay contacts to drive whatever you want (under 3A). Pair that with a cheap wall wart and a cheap contactor/high amp relay and you're good to go. The great thing about single cells, is that you can use automotive relays/starter relays since the voltage is under 12V.

Power supply (charger) + the Volt meter above (5740TV) + wall wart you probably already have + starter relay for a motorcycle = voltage limited HVC charger.

total would likely be under $60 without the charger.


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## dtbaker (Jan 5, 2008)

ok, getting back to this project.... I think I am going to try assembling what I need using:

$11 - voltmeter/relay
http://www.ebay.com/sch/i.html?_trk...3&_nkw=12v+voltmeter+relay&_sacat=0&_from=R40

$64 - 110vAC - 12vDC, 50amp power supply (600watt)
http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313&_nkw=12v+50a+power&_sacat=0&_from=R40

I'm picking the 12v power supply because it can power the relay with a direct jumper from output and not require a separate power supply.... The 12v output should be high enough to be sure that the voltage diff is enough that the power supply pumps full current to the cell.

only question I have is that when the voltmeter/relay turns off the AC input to the power supply, will it STAY off, or bounce on and off as the cell voltage relaxes and then rises back to target end voltage.

what would I need to add so that once the relay opens to end the AC input, it STAYs off until I move to the next cell and reset?


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## frodus (Apr 12, 2008)

You get another 12V relay....and wire it so that it latches itself when you hit a start button. When the voltmeter relay disengages, it interrupts the latch line on the relay.

Search google for latching relay circuit.


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## dtbaker (Jan 5, 2008)

frodus said:


> You get another 12V relay....and wire it so that it latches itself when you hit a start button. When the voltmeter relay disengages, it interrupts the latch line on the relay.
> 
> Search google for latching relay circuit.


ok, search turns up all kinds of 12v latching relays, several in the $10 range. I'm just not sure which would do the job. would I need a physical button or switch as well to 'energize' the latching relay, which energizes the voltmeter/relay unit?

pardon my ignorance, but I'm unfamiliar with relays and switching and latching.... I guess I need a sketch of a schematic or something to visualize.

I have never dealt with the concept of latching, so am in new waters.....


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## Ziggythewiz (May 16, 2010)

I still say anything over 5V is too high to try charging a LiFePO4 cell. 12V is crazy high.


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## Ziggythewiz (May 16, 2010)

This post shows a diagram of a relay tied to itself (used for precharge). There's some discussion as well to help slow people like me understand.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> I still say anything over 5V is too high to try charging a LiFePO4 cell. 12V is crazy high.


why does it matter whether the power supply is 4,5,6, or 12v? aren't we only concerned with the current going in (limited by the power supply), and turning if off when the cell voltage hits the limit?


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## dimitri (May 16, 2008)

dtbaker said:


> (limited by the power supply)


There is your problem, current is not limited by supply because these are CV supplies, not CC supplies. Your supply's over-current protection will kick in and shut it off. 12V is too much voltage difference for single cell.

You should have gotten 5V supply as I recommended in my posts.


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## frodus (Apr 12, 2008)

dtbaker said:


> ok, search turns up all kinds of 12v latching relays, several in the $10 range. I'm just not sure which would do the job. would I need a physical button or switch as well to 'energize' the latching relay, which energizes the voltmeter/relay unit?
> 
> pardon my ignorance, but I'm unfamiliar with relays and switching and latching.... I guess I need a sketch of a schematic or something to visualize.
> 
> I have never dealt with the concept of latching, so am in new waters.....


I was really trying to avoid having to do all the research for you.... 

You don't need a different latching relay. Just a normal 12V relay with 2 sets of contacts (double pole/single throw).

http://users.senet.com.au/~dwsmith/Boolean/ilfig1.gif

SET is the "start" button
Reset is the voltmeter relay contacts

When the start is initiated, the relay supplies it's own power through it's second set of contacts/voltmeter relay. When the voltmeter triggers it's ouput, it can interrupt the Reset line, which unlatches the relay.

You're also missing a 50A contactor in this equation. How are you going to turn the power supply on and off?


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## dtbaker (Jan 5, 2008)

dimitri said:


> There is your problem, current is not limited by supply because these are CV supplies, not CC supplies. Your supply's over-current protection will kick in and shut it off. 12V is too much voltage difference for single cell.
> 
> You should have gotten 5V supply as I recommended in my posts.



ooohhh, I was thinking that the power supply would clamp down and just hold itself to max current, not turn off. hhhmmm, maybe I can cancel the buy . ;(


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## dtbaker (Jan 5, 2008)

frodus said:


> I was really trying to avoid having to do all the research for you....


I'm not afraid of research, but don't know what to look for in this case. So, thanks!




frodus said:


> You don't need a different latching relay. Just a normal 12V relay with 2 sets of contacts (double pole/single throw).
> 
> http://users.senet.com.au/~dwsmith/Boolean/ilfig1.gif
> 
> ...


ok, I'll study this......



frodus said:


> You're also missing a 50A contactor in this equation. How are you going to turn the power supply on and off?


the voltmeter/relay says it can handle switching 12amps at 110vAC, so I was going to just use it to turn the power off on the INPUT side of the power supply, no secondary contactor required. Won't that work?


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## Ziggythewiz (May 16, 2010)

dtbaker said:


> why does it matter whether the power supply is 4,5,6, or 12v?


There's a reason we use chargers that are designed or programmed for a specific voltage and not just any charger that's arbitrarily higher than pack voltage.

Outside the operating range of any charger (or power supply) you'll trip limits or blow fuses if lucky, or create a magic smoke factory if not.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> There's a reason we use chargers that are designed or programmed for a specific voltage and not just any charger that's arbitrarily higher than pack voltage.
> 
> Outside the operating range of any charger (or power supply) you'll trip limits or blow fuses if lucky, or create a magic smoke factory if not.



so..... would this work? 5v output, says 28amp max.... lots more expensive at $199, but that would be ok all things considered in time savings for a quicker charge.

http://www.ebay.com/itm/Acopian-5PH...521?pt=LH_DefaultDomain_0&hash=item257b175891


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## frodus (Apr 12, 2008)

dtbaker said:


> the voltmeter/relay says it can handle switching 12amps at 110vAC, so I was going to just use it to turn the power off on the INPUT side of the power supply, no secondary contactor required. Won't that work?


It might, but be darned sure that no power can go from the battery INTO the power supply when it's off, otherwise it'll drain the battery. 


Lets stop a minute though....

Here's what I would do. Get a real charger made by folks that know how to charge a battery and design a charger.

Scratch everything and buy a decent charger like a powerlab 6:
http://www.revolectrix.com/PL6_specs_tab.htm

get a decent 12V supply (like you bought), adjust for max current and let it go. It's a~ 40A charger.


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## dtbaker (Jan 5, 2008)

frodus said:


> Scratch everything and buy a decent charger like a powerlab 6:
> http://www.revolectrix.com/PL6_specs_tab.htm
> 
> get a decent 12V supply (like you bought), adjust for max current and let it go. It's a~ 40A charger.



ok, I'm not married to cobbling it together myself, I'd much rather buy.  The $175 for the PowerLab6 is a little higher than I'd prefer, but it looks super sophisitcated. Adding the 12v power supply for $65 seems like a reasonable solution, the total is about what I was prepared to pay for a dedicated charger.......

looks like a plan to me. I'll leave the component design to the EEs....


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## frodus (Apr 12, 2008)

The Powerlab is a pretty robust device, and if you use a 12V battery on the input, you can use it as a discharger as well. You can also test batteries (like the West Mountain Radio CBA) and plot nice curves for batteries.

I think you'd be getting a hell of a charger for $65 + $175 = $240


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## dtbaker (Jan 5, 2008)

frodus said:


> The Powerlab is a pretty robust device, ...
> 
> I think you'd be getting a hell of a charger for $65 + $175 = $240


well..... I've ordered, so will post results after I try it out!


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## frodus (Apr 12, 2008)

Yeah, we need more single cell chargers IMHO... hope it works.

If it doesn't work well, they're easy to return/sell.


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## dtbaker (Jan 5, 2008)

frodus said:


> Yeah, we need more single cell chargers IMHO... hope it works.
> 
> If it doesn't work well, they're easy to return/sell.



my goal is to have a quicker way to do the initial top-balance, and the occasional maintenance balance. Using my cheap Mastech power supply was painfully slow, and using CV was the only way I could leave it unattended, which gets even slower the closer to 'done' it gets.

I would hope that if one of the EE types here sees there is a market for fixed parameter 'quick balancer', it might be able to build one for cheap and still have enough margin to be worth building.


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