Page 1 of 1

Building a cheaper charger

Posted: Sat Sep 11, 2010 6:16 pm
by retepsnikrep
Started this thread to discuss using cheap Switch mode power supplies controlled by the BMS for charging.

S-350 range of meanwell power supplies work well and are easy to mod.

I am using 3 x 48v units modified to provide 60v at 5.5A to charge a 20ah x 50 cell pack in 4 hours.

The info comes from this thread on the endless sphere forum. ... =14&t=4125

I bought them from the below, came in about 10 days from china. Three chargers came to about $110 which is very cheap compared to a 'proper' EV battery charger. I paid over £500 for my last Zivan charger and it took two months to arrive :(

48v items - Get great deals on Tools, Prototype PCBs items on Shops!

I'm using them to charge my 50 x 20ah A123 cell pack. I have them running at 60v and 5.5A output.

They seem pretty easy to mod, with all the bits identified in the endless sphere forum threads in the right places on the pcb.

The three supplies all have the following mods.

1) Fan mod to activate fan as soon as psu is turned on. Simple 470R resistor inserted instead of thermistor.
2) Raised output voltage mod. Simple replacement of 2k resistor with a 1.2k device to push up the operating voltage range window.
2A) Replacement of over V voltage detection zener with a 68v device to enable 2) above.

One of the psu's (Let's call it the Master) has three further mods.

1) Current limit mod to lower output current so total supply power does not exceed 350w or so. I started by removing one of the three shunts on the pcb reducing output current by a third.
2) I then removed R33 and added a 500R pot into the free space on the pcb at SVR2 and a link at R27. Gives fully variable current limit.
3) I also brought out two connections which bridge the output voltage pot to use that to remotely control the operating voltage later. Perhaps via a digital pot.

All three psu's in series should run at the current as determined by the Master.

The charger is controlled in three ways.

1) The total output voltage of the combined psu's is adjusted to the pack full voltage limit or a tad below. So they limit themselves when output voltage rises to the preset maximum. So if the BMS fails and the pack is reasonably balanced it should be impossible for them to overcharge the pack.

2) The BMS controls the output voltage of the Master Psu. If a cell goes over V it can cutback the voltage of the the master PSU reducing charge current.

3) The BMS controls the solid state mains relay which powers up all three Psu's. If a cell goes over V and it can not be corrected by 2) above then the mains can be cut.

You can make higher current charger using a higher number of the lower voltage supplies.

I used to have giant 50A charger for my 200ah TS cells made using two 3kw 48v server psus in series. It worked very well!

Re: Building a cheaper charger

Posted: Sun Sep 12, 2010 9:46 pm
by GregsGarage
I am jumping on this bandwagon as well. :) I have ordered 3 of these. They are Lutze WRA960 48 volt 20 amp supplies. Note that they require 3 phase 415v mains power, so I will be mounting these at my work where 3 phase is available, most homes won't have 3 phase power so check before rushing out and buying these. They have a voltage trim adjustment and when connected together in series, will charge my pack to 3.5 volts per cell, and should give me a nearly full pack in 6 hours.

Edit: received the power supplies, will post pics when I get them installed.

Re: Building a cheaper charger

Posted: Tue Sep 21, 2010 5:52 am
by retepsnikrep

Re: Building a cheaper charger

Posted: Tue Sep 21, 2010 11:37 am
by Jeremy
That thread on ES has spawned a life of its own! I started it over two years ago and it simple refuses to lay down and die................

My original Meanwell S-350 power supply, modified as a charger, is still working very well BTW. I added the current limit mod, as well as the high voltage mod and it seems pretty bombproof. I've since bought quite a few more of these supplies and (touch wood) haven't had any problems with them. One is even driving a big brushless motor on my milling machine with no sign of stress.


Re: Building a cheaper charger

Posted: Tue Sep 21, 2010 12:15 pm
by retepsnikrep
Jeremy you are a man of many talents Image

Re: Building a cheaper charger

Posted: Wed Sep 22, 2010 3:58 pm
by dillond666
I happened upon this article a few days ago and was most interested. ... -6795.html

As my interest has been piqued I have ordered a book on power electronics and two on switch mode power supplies :shock:
Every time I twiddle the pots on my Zivan I get nervous. It was expensive so why am I not in full control of it?
I reckon when my BMS is shunting, it confuses the Zivan and stops the current from tapering down as it's supposed to.
More homework definitely required :lol:


Re: Building a cheaper charger

Posted: Thu Oct 21, 2010 10:54 am
by martinwinlow
Peter et al...

On the subject of cheap (and powerful) DIY chargers, have you come across this thread .... ... ht=charger ...??


Re: Building a cheaper charger

Posted: Thu Jan 27, 2011 8:54 pm
by jackbauer
I built this charger over a year ago using mostly parts rescued from a scrap plasma cutter. Still going strong and hold voltage very well:

Re: Building a cheaper charger

Posted: Mon Feb 28, 2011 9:49 am
by retepsnikrep
I tweaked my charger setup today to get the current limit while balancing stage correct. :roll:

As mentioned above I had added a 500R pot to adjust the current. I removed this from the board and added two pots to the outside of the case so i could get to them.

1) 1K 10 TURN permanently connected this is the bulk phase and adjusted on my setup to 6.5A

2) 50R 10 TURN in parallel to the above but only active (in parallel) when 12v micro relay activated by charger cutback opto on BMS master board.

Once the 50R is in parallel to the 1k charge current drops right down and can be adjusted to whatever you want for the balancing phase. I selected 300ma.

So you have two seperate adjustable limits :) If you remember from my recent post on the software thread I added a test option in submenu three to toggle on/off the charger opto for testing purposes so you can adjust it at any time :)

Also the voltage output of the three supplies I use in series is adjusted to match the fully charged voltage of the pack. So if the BMS all fails then the pack can't go above the fully charged pack voltage anyway. Hope that makes sense.