Jeremy Harris
100 MW
I took a gamble and purchased one of these: http://cgi.ebay.com/350W-48V-7-2A-S...ryZ48632QQssPageNameZWDVWQQrdZ1QQcmdZViewItem to see if I could mod it to run at about 60V. The idea is to use it as an on-board charger for my motorcycle build, which is using a 48V, 40Ah Headway LiFePO4 pack.
Today I took the PSU apart and spent a couple of hours reverse engineering it. I believe that these supplies are available from several different suppliers, all with essentially the same design, usually with a number like "S-350-48". The supply is based around the TL494 PWM chip (see here http://focus.ti.com/lit/ds/symlink/tl494.pdf for details). It's easy enough to up the voltage range, by simply adding a 15k resistor across the 3k9 resistor adjacent to the voltage trim pot. The snag is that the over-voltage protection circuit kicks in at about 53 volts, so seriously limiting the ability to trim the output up.
The fix for this is easy. Underneath the main ferrite transformer there is a 53V zener diode, labelled ZD1. Simply unsolder one end of this and add a 10V zener in series. This ups the over-voltage protection to 63V, which is the same as the rating of the main output filter caps.
The supply is good for over 6 amps (as high as I've tested it) at 60V, with no problems. I reckon it will make a neat on-board charger. All I need to get on and build is a shunt regulator type charge management system, like the excellent one from Gary/Bob. I've already got one of Gary's LVC cut-off boards, to switch off the controller in the event of a cell going low.
I love it when a plan comes together...................
Jeremy
Today I took the PSU apart and spent a couple of hours reverse engineering it. I believe that these supplies are available from several different suppliers, all with essentially the same design, usually with a number like "S-350-48". The supply is based around the TL494 PWM chip (see here http://focus.ti.com/lit/ds/symlink/tl494.pdf for details). It's easy enough to up the voltage range, by simply adding a 15k resistor across the 3k9 resistor adjacent to the voltage trim pot. The snag is that the over-voltage protection circuit kicks in at about 53 volts, so seriously limiting the ability to trim the output up.
The fix for this is easy. Underneath the main ferrite transformer there is a 53V zener diode, labelled ZD1. Simply unsolder one end of this and add a 10V zener in series. This ups the over-voltage protection to 63V, which is the same as the rating of the main output filter caps.
The supply is good for over 6 amps (as high as I've tested it) at 60V, with no problems. I reckon it will make a neat on-board charger. All I need to get on and build is a shunt regulator type charge management system, like the excellent one from Gary/Bob. I've already got one of Gary's LVC cut-off boards, to switch off the controller in the event of a cell going low.
I love it when a plan comes together...................
Jeremy