# 48v charger solution



## glyndwr1998 (Apr 27, 2013)

Hi Yabert,

I use a meanwell rsp 750 48 to charge 7 leaf cells in series with no problems.
The potentiometer can adjust the set point up to 55vdc, as ow as 44vdc.
I use leaf cells connected to a ups for emergency power backup, been working for over a year with no problems.

I use bms to cut off power to the charger when ant cell gets to 4.1v.

Anthony.


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## Yabert (Feb 7, 2010)

Thanks to share experiment.
I guess you use a bms to stop the charger because without it the power supply will always stay ON, right?
I'm not sure to fully understand if in this case the power supply will simply stay ON indefinitely and supply 0A to the battery.

I would like to know if this kind of powersupply have some dificulty to start to charge a battery at low voltage. Let say all the cells are at 3v (36v), is the powersupply will turn ON and provide 21A (in case of a 48v-1000w model)?


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## Yabert (Feb 7, 2010)

Some useful information about using a power supply as battery charger:
https://endless-sphere.com/forums/viewtopic.php?f=9&t=51833
http://electricmotorcycleforum.com/boards/index.php?topic=4523.0
http://electricmotorcycleforum.com/boards/index.php?topic=3085.0

... but still no clue to how stop the power supply when it reach full voltage. Maybe a simple time delay relay?


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## glyndwr1998 (Apr 27, 2013)

In my set up, when any cell reaches 4.1v, the bms signals a relay to cut the AC power to the power supply, very simple AC power relay. Also I have a voltmeter to also cut AC relay if pack voltage is too high, although, if the power supply potentiometer is adjusted correctly, at max pack voltage the power supply delivers no amps. Ok, this isn't good to float lithium cells, but at least it can act as another stop system to ensure your not overcharging and overheating th cells.

my meanwell power supply has current limiting built in so if the cells are really low the power supply will supply max current but not overload itself.

Thanks.


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## Yabert (Feb 7, 2010)

Thanks for details.

Is anyone know a low cost solution to stop those RSP power supplies when they reach a determine voltage or, better, when the load is reduced to few Amps?


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## PStechPaul (May 1, 2012)

I built a simple voltage monitor relay that would work for this. See my thread:

http://www.diyelectriccar.com/forums/showthread.php?t=84319&highlight=voltage+relay

You could do it with an Arduino or any similar microcontroller. 

Something else I found:

http://www.pssurvival.com/PS/Batter...Battery_Voltage_Monitoring_Switching_2010.pdf

And this is what some people use for EV battery pack monitoring and charge control:

http://www.lithiumbatterypack.co/EC...-br-Amp-Hour-Counting-br-USA-Stock_p_300.html


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## glyndwr1998 (Apr 27, 2013)

In use cell loggers to monitor each cell, and have these set to activate the relay output of the device when any cell reaches 4.1v or 3.5v.
So that's the cells covered individually.

I also use a jld404 to read the total pack voltage and set that to trip a relay when the max or min pack voltage is reached.

Quite cheap and simple to acheive and has been very reliable.

On endless sphere you will find a lot if info about using cell loggers for cell level control. 

Have fun.


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## Yabert (Feb 7, 2010)

Yea, use the jld404 or build a voltage relay to stop the power supply (I'm not interested to per cell cutoff). First solution: add 100$ to a 200$ charge system don't seem smart to me. Second solution... well maybe a bit over my electronic capability.

Well, the best still be to stop the power supply when his load is reduce (mean it reach C-V phase). How is it possible to do this with a RSP?


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## glyndwr1998 (Apr 27, 2013)

I've also used the cheaper Chinese programmable volt and current meters below, they work pretty well to be honest for th money.

http://www.ebay.co.uk/itm/Programma...824407?hash=item2a556cdd97:g:VYkAAOSwgQ9V4xwJ

In addition, I'm sure there isn't anupything that can be done to the power supply to cut it out at the top of its charge.

Maybe you could time the charge process then maybe add a timer relay and set the timer relay to cut the power supply once th ax time has been reached.

Good luck with whichever method you choose to deploy.


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## BVH (Jul 4, 2014)

A little pricey but programmable and bullet proof. 8 Amps max.

http://www.ebikes.ca/product-info/cycle-satiator.html

I've had mine for a couple of years no issues.


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## Yabert (Feb 7, 2010)

BVH said:


> A little pricey but programmable and bullet proof. 8 Amps max.


Yes, probably a good product. The compact size is nice for e-bike, but this price for only few hundred watts it not justifiable for a regulat application.


Come back to power supply idea. I can't believe there is no easy way to stop a RSP-power supply when the output power reach 0w...
Any thought?


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## PStechPaul (May 1, 2012)

Depends on what you consider easy. Remember that the power supply must have a voltage greater than the maximum charge voltage of the battery pack. You can set the PSU to that voltage, and use a current regulator to charge at a fixed current up to that point, at which it will act as a float charger. But because of the resistance of the battery pack and connections, the target voltage will be reached before a full charge is obtained. This effect will be greater at higher charge rates.

The charging profile of lithium batteries is such that the voltage rises immediately when charge current is first applied, and it may take quite a bit higher voltage than the final target in order to get enough current. Then the voltage stays relatively constant until about 80% DOC, at which point it will rise fairly quickly. A good charger will, at that point, reduce current to C/10 or C/20, at which point the voltage will drop, and then it will start rising again near full charge.

There are also temperature effects and differences between batteries, so you need to be sure the pack is top balanced to do a simple cut-off based on total pack voltage. If one cell becomes weak, it may be overcharged unless you have a good BMS.


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## Yabert (Feb 7, 2010)

Thanks Paul, I know all that.
The advantage of the Meanwell RSP PSU is they are in continuous current mode when the voltage is lower than the setting voltage.
The other advantage is I plan to charge at around C/5 rate from a 120v outlet, so when the C-C mode will end, the C-V mode will be short.

A nice thing could be to use some current regulator parts in the PSU to know when the output current is low.
Low output current = end of charge.
Idea?
https://www.trcelectronics.com/ecomm/pdf/rsp1000.pdf


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## PStechPaul (May 1, 2012)

I'm not familiar with that RSP1000 PSU but it appears that the 48V nominal unit can be programmed for 43-55V but the current limit seems to be fixed at 21 amps. Perhaps you plan to use a lower power model for C/5 charging. A 15A 120V outlet is good for 1800 watts but best to limit use to 1500 watts.

I assume that the battery pack is rated 100 A-h so the 21A is about C/5. I suppose you can just set the output to 49.2 volts and let the current limit take control until the voltage reaches that level. Still, it would be advisable to use a BMS and possibly a timer to shut down the charger after 5 or 6 hours.


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## Yabert (Feb 7, 2010)

Exactly Paul, except one thing. From my understanding of this PSU, it will automatically be in overload in C-C mode when it act as charger.
Since the overload is allowed up to 125% the output current will be around 26A.
26A x 49,2v / 0,9 (efficency) = 1420w on the AC line. Everything seem good to me except that it will never turn OFF by itself.
With a MiniBMS it's a 204$ solution to turn off the charger.... and hypothetically protect the cells.

So bad I don't have a better understanding of electronic and control, if no I would find a solution to turn OFF the PSU or better, re-use the Chevy Volt BMS...


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## PStechPaul (May 1, 2012)

You could try this for $12:

http://www.ebay.com/itm/13S-48V-Li-...tection-BMS-PCB-Board-w-Balance-/162159423979

or

http://www.ebay.com/itm/13S-48V-Li-...tection-BMS-PCB-Board-w-Balance-/331735442078

or

http://www.ebay.com/itm/48V-PCM-Bal...ithium-battery-protection-board-/131913261174

or (48V LiFePO4)

http://www.ebay.com/itm/48V-30A-16-...-BMS-Protection-Board-balancing-/301732161823

or

http://www.ebay.com/itm/30A-48V-16-...-Protection-Board-BMS-Balancing-/141771638553

There are many others, some are called charger protection circuits.


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## Yabert (Feb 7, 2010)

I finally test the toy. This 1000w power supply is simply super.
Slim, powerful, 26A continuous up to adjustable end voltage (49v in my case)... everything is fine.

It don't stop by itself after the current reach 0A, but it's fine at the moment.


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## Karter2 (Nov 17, 2011)

The Meanwells i have used have ramped down to 0.00 amps if left on.
They wont overcharge if you have the voltage set correctly.
A simple time switch as back up cut off is all i have ever needed


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## Karter2 (Nov 17, 2011)

PStechPaul said:


> The charging profile of lithium batteries is such that the voltage rises immediately when charge current is first applied, and it may take quite a bit higher voltage than the final target in order to get enough current. Then the voltage stays relatively constant until about 80% DOC, at which point it will rise fairly quickly. A good charger will, at that point, reduce current to C/10 or C/20, at which point the voltage will drop, and then it will start rising again near full charge.
> .


....thats not like any lithium charge profile i have ever seen !
Every charge profile i have logged ( and seen) shows the voltage (applied to the cell) to rise steadily whilst the current is in CC phase all the way until the voltage reaches the set charge voltage.
Then the voltage holds steady with no change in voltage ,whilst the current decays slowly to the preset cut off (c/10-c20) 
I have not seen any rise/fall/rise again behaviour of the charge voltage.
https://goo.gl/images/uQtSP4



> ..Ref Texas Instruments..
> . If a Li-ion battery is deeply discharged (for example, to below 3 V) a small “pre-conditioning” charge of around 10% of the full-charge current is applied. This prevents the cell from overheating until such a time that it is able to accept the full current of the constant-current phase. In reality, this phase is rarely needed because most modern mobile devices are designed to shut down while there’s still some charge left because deep discharge, like overcharging, can damage the cell.
> 
> Image of li-ion charging profile
> ...


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## PStechPaul (May 1, 2012)

I've only had limited experience with discharge and charge profiles of lithium cells, and I had some problems with my test setup. Plus they were cheap 18650 cells supposedly 3600 mAh and actually much less. Here is a rough chart of the data - you can see where I had some measurement problems:










The discharge was a little better controlled:










I think I measured a rather high internal resistance which may have been the reason for my thoughts about the charge profile. But the salient point is that at a constant current charge, the voltage may jump up from the open circuit value, and then will probably rise fairly quickly to a certain level after which it will rise only a little bit, until near end of charge, where it will rise quickly. At that point, AIUI, the current is usually reduced to about C/20 until the voltage rises again at full charge. But that final low current charge may not really be all that useful, as the additional charge may be only about 5% whereas it may reduce the lifetime of the cells.


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## Karter2 (Nov 17, 2011)

Paul, what were you charging with ?
That is definitely not a typical charge profile.
Im having trouble posting images from this ipad so i hope you could see the profiles in the link i posted previously.
The only time the voltage is higher than the final charged cell voltage (4.2v) would be before the charger is connected to the cell.
.try this stock image..
Note also, if you stop charging without letting the current decay in the CV phase , you lose at least 15% of potential capacity.


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## riba2233 (Apr 29, 2015)

PStechPaul said:


> I've only had limited experience with discharge and charge profiles of lithium cells, and I had some problems with my test setup. Plus they were cheap 18650 cells supposedly 3600 mAh and actually much less. Here is a rough chart of the data - you can see where I had some measurement problems:
> 
> 
> 
> ...



Yep, shit cells with very high IR. Not representative


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## Karter2 (Nov 17, 2011)

PStechPaul said:


> ?...... Plus they were cheap 18650 cells supposedly 3600 mAh and actually much less. .....
> .


Any 18650 cell claiming to be more than 3500mAhr should be considered with great suspicion !


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## riba2233 (Apr 29, 2015)

Yeah, except for panasonic 18650G which is 3600 mah but only available to oems


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## PStechPaul (May 1, 2012)

I had made a datalogger with voltage and current measurement via differential amplifiers to the ADC inputs of a PIC. I think I used a power resistor and an adjustable power supply for the current. I had some connection problems at the beginning and also some zero drift and common mode error. Plus the crap cell with probably 0.15 ohms or more internal impedance (0.3V drop at 2 amps). I was going to do more testing but it seemed rather pointless.

I think I paid only about $3 each for the two cells and I got a 50% refund when I reported the problem. I had also purchased some LiFePO4 cells supposed to be 1800 mA-h and they were also overrated, but actually had about 1200 mA-h. Not quite as bad:


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## Karter2 (Nov 17, 2011)

For ~$50 you could buy a programmable 20-30amp RC charger with data logging of V, A, temp, time , etc.


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