I picked up one of these recently and thought I'd give it a once over. It looked quite compact, came with a fan, already had an XT60 connector and I could do with something that charges a bit faster than my SANS chargers. It uses a PSU PCB company that also makes the PSU boards for the Vruzend brand. In fact, it looks physically very similar to the Vruzend PSU.
Vruzend PSU from Ad:
Back of the Mike's eWheels PSU:
It is quite a lot more compact and lighter than the SANS chargers. The mains cable is fixed, which may or may not be a disadvantage.
Including all cables, it weighs 350g.
It comes with an XT60 connector, which is good, but there is nothing filling in the gaps at the back of the connector.
The fan only comes on when charging. I have not tested charging current yet, but the voltage output was 41.9 V
The next question is whether it can be tuned to 41V to improve battery cycle life.
Unfortunately, unlike the SANS chargers (and the Vruzend 14s charger I bought a while back), there isn't a pot for easy adjustment:
The quality of the soldering was ok, There was only one poor quality joint, the one around the gate on the high voltage side MOSFET. However, there was some solder spatter in places, that could come detached eventually and could cause shorts.
The Vruzend PSU for a 14s battery pack also had a poor joint on one of the high voltage side capacitors. Seems like something you have to check for yourself on anything that comes from China these days.
As there is no pot for easy adjustment, the PSU must have been adjusted in the factory with discrete components. The question is, which part of the circuit? Typically on switched mode PSUs there are a couple of TL431 voltage regulator ICs, one for current regulation and one for voltage. The voltage regulator often connects to the opto coupler, which controls the high voltage side, here is an example from the web:
Close examination showed that someone had manually placed and soldered R22 and R23. They make part of a voltage divider (top part in Red circle) between the positive output and ground and connect to the TL431 (Yellow circle), connected to the opto coupler (Blue circle). So rather than fit a pot for easy adjustment, to save a few pennies on a pot, someone has manually fiddled with surface mount resistors to tune the output to just under 42V. Labour is cheap I suppose...
So, if the value of this divider is changed, will I change the output voltage?
The top resistor is zero Ohms, so the easiest thing to do was remove that and change the resistance of the resistor chain just a fraction, in case it wasn't the right part of the circuit for voltage control - I wouldn't do much harm and it could easily be reverted to pre hacked status. I temporarily soldered in a 220 Ohm resistor:
Result! the voltage increased to 42V with the 0 Ohm resistor replaced, while it went back to 41.9V ahen the 220 Ohm resistor was shorted. So the next thing to do will be to reduce the resistance of the resistor chain, as increasing it has raised the voltage. I will do this later and report back, as it means either removing one of the higher value resistors or putting another resistor in parallel with the existing resistors. But it will need a little more fiddling.
Anyway, it looks like I've found the right component to change and by dropping the overall resistance by about 1k, I should get an output of 41V.
Hopefully this may be useful to people out there who also have PSUs without pots for manual adjustment of output voltage.
Vruzend PSU from Ad:
Back of the Mike's eWheels PSU:
It is quite a lot more compact and lighter than the SANS chargers. The mains cable is fixed, which may or may not be a disadvantage.
Including all cables, it weighs 350g.
It comes with an XT60 connector, which is good, but there is nothing filling in the gaps at the back of the connector.
The fan only comes on when charging. I have not tested charging current yet, but the voltage output was 41.9 V
The next question is whether it can be tuned to 41V to improve battery cycle life.
Unfortunately, unlike the SANS chargers (and the Vruzend 14s charger I bought a while back), there isn't a pot for easy adjustment:
The quality of the soldering was ok, There was only one poor quality joint, the one around the gate on the high voltage side MOSFET. However, there was some solder spatter in places, that could come detached eventually and could cause shorts.
The Vruzend PSU for a 14s battery pack also had a poor joint on one of the high voltage side capacitors. Seems like something you have to check for yourself on anything that comes from China these days.
As there is no pot for easy adjustment, the PSU must have been adjusted in the factory with discrete components. The question is, which part of the circuit? Typically on switched mode PSUs there are a couple of TL431 voltage regulator ICs, one for current regulation and one for voltage. The voltage regulator often connects to the opto coupler, which controls the high voltage side, here is an example from the web:
Close examination showed that someone had manually placed and soldered R22 and R23. They make part of a voltage divider (top part in Red circle) between the positive output and ground and connect to the TL431 (Yellow circle), connected to the opto coupler (Blue circle). So rather than fit a pot for easy adjustment, to save a few pennies on a pot, someone has manually fiddled with surface mount resistors to tune the output to just under 42V. Labour is cheap I suppose...
So, if the value of this divider is changed, will I change the output voltage?
The top resistor is zero Ohms, so the easiest thing to do was remove that and change the resistance of the resistor chain just a fraction, in case it wasn't the right part of the circuit for voltage control - I wouldn't do much harm and it could easily be reverted to pre hacked status. I temporarily soldered in a 220 Ohm resistor:
Result! the voltage increased to 42V with the 0 Ohm resistor replaced, while it went back to 41.9V ahen the 220 Ohm resistor was shorted. So the next thing to do will be to reduce the resistance of the resistor chain, as increasing it has raised the voltage. I will do this later and report back, as it means either removing one of the higher value resistors or putting another resistor in parallel with the existing resistors. But it will need a little more fiddling.
Anyway, it looks like I've found the right component to change and by dropping the overall resistance by about 1k, I should get an output of 41V.
Hopefully this may be useful to people out there who also have PSUs without pots for manual adjustment of output voltage.
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