Meanwell Bulk Charger
Converting a MeanWell S-350-48 into a LiPo Bulk Charger
If you have an e-baike with a 44V LiPo battery pack, and decide that you want to bulk charge it, you can buy a dedicated battery charger for over $100, or you can make you own with an inexpensive MeanWell 48V power supply, some extra parts, and some careful soldering.
May 2011
The MeanWell power supply has an adjustable voltage, and should be set to 49V for a 12S LiPo pack. If an unmodified MeanWell is used to charge your battery pack it will charge at the maximum current due to the low impedance of the batteries. This will eventually cause the  power supply to burn out. To prevent this, you will need to modify the MeanWell to limit the current. Note that there are lots of fake MeanWell supplies available on EBay.

These pictures can be clicked on for a higher resolution view.

Here are the wires from the potentiometer soldered to each end of R33.

I wanted a way to adjust the current from outside the chassis, but it looks like that is not really needed. Last night I connected my depleted LiPo pack to the MW PSU, and I used the 5K 1T pot to adjust the currrent. When the pot is set for open circuit, the MW tries very hard to charge the pack, and runs at about 9.5 amps. At 50V thats 475 watts, way over the 350watt rating.



I used the Fluke VOM to measure the current while charging a LiPo 12 S (49V fully charged) battery pack, while varying the potentiometer.

Adjusting the pot reduces the current. Below about 4 Amps I heard the power supply buzzing, so I adjusted it up to about 6 amps. I then measured the resistance of the pot. It was about 500 ohms.

 

I looked in my electronics bin for a suitable resistor, found one that was 575 ohms, and hard-wired it in place of the pot. I thought I may want to add a pot later, so I connect it it to the wires and stuck them to a capacitor with a blob of glue to prevent it from vibrating around.

When I fired the PSU back up it was charging at about 6.5 amps, which is within the rated specs of the MW PSU.

The fan went on and off as the PSU heated up and was then cooled by the fan. Nice. The LED voltage meter on the PSU displayed the charging battery voltage, so I was able to keep track of the charging process. As the battery voltage got close to the voltage set on the PSU (49V), the current began to drop. This made the charging slower. I finally disconnected the pack when the current dropped to about .5 amps. I have heard that this may never go to 0 amps, so this is probably not the solution to leave unattended overnight. 

I'm pretty happy with this, and it will be a good way to charge the battery at work. This was my first bulk charge. I'll check to check the individual cell voltages tonight to ensure they are not getting all unbalanced.
That blue volt meter does not normally come with the MeanWell PSU. Once you have the current limiter installed and adjusted the current limiter, it's nice to have a way to monitor the charging progress. One way to do this is to install a panel mount voltage meter. These are available on eBay for around  The one I bought was "Mini 99.9VDC Blue Digital Panel Meter Voltmeter" for about $10.

In addition to the voltage to measure, the voltage meter requires a 12V power supply. Fortunately the MeanWell power supply has 12V that is easily accessible. Just solder the + wire for the 12V voltage meter supply to the top of R52 as shown.

I soldered the ground and voltage sense wires to the backs of the screw connectors.

It works!

On this voltage meter there is a tiny potentiometer to fine tune the voltage.

I used a nibbler tool to cut a hole in the top of the case to mount the meter. I should have mounted it more to the lower right of the case as the back of the meter contacts a heat sink when it is fully closed. I'm using a plastic insulator to ensure it doesn't short out.
Another common modification is to add a switch to make the fan stay on all the time, rather than letting it turn on and off by itself. This is known as the Q5 emitter/collector fan mod.

Credits to NeilP and Amanda for the fan mod info.

Here's the location of Q5 on the Meanwell. To make the modifications, you will need to remove the power supply board completely.
Here's the back of the circuit board where you need to solder the wires that go to the switch. Click on the image to see the picture big enough to read.
Here's the inside of the case that Neil P made for two Meanwells. It allows him to switch them into series or parallel mode.
Here's Neil's Meanwell charger case with switches to turn on and off the fans, voltage adjustment, and the ability to change from series to parallel mode. Very clean.
A better option for a charger to be used to bulk charge LiPo and will actually shut off when the battery is fully charged is this one from BMSBattery.com. They cost about $120 with shipping. This Chinese company does not communicate well, but the product is decent and does arrive, eventually. You can have them configured to the voltage you desire.

 

I tested it and it works well, charging the battery to the desired 49V before shutting off.

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