Hi guys,
I have a pretty mad idea to build a super high current lead acid battery charging system on the cheap, using a TIG welder as the power source. Yes, this is potentially very dangerous. So lets get down to the engineering.
Intro
I've recently aquired 11x 92 Ah 12 V batteries that I will be using in a UPS backup system of my own design, all of which will be connected in parallel for charging and discharging. Clearly this battery bank requires a significant charging current - 0.08 to 0.1 C is recommended for a "slow" charge, equating to a charge current of 80.96 A to 101.2 A. Lead acid's require a CV / CC combination to charge correctly, meaning I need excellent control of the output of the TIG welder if this project is going to be possible.
Why Parallel Batteries?
It's a lot easier to find high power (3000 W) 12 VDC to 230 VAC inverters than it is ones that accept 130 / 140 VDC inputs. Additionally, it's easier to charge a bank of parallel 12V lead acids than a series stack (balancing for example).
Why a TIG welder?
There are not many sources of such high current power available to the domestic market for a price that is anything like reasonable. However, due to the magic of globalisation and economies of large-scale manufacturing, we can purchase high current TIG welders for a very reasonable price (for example £130 for a 140 A IGBT variant on Amazon - less than £1 per amp!!). On the face of it, these machines are very nicely suited:
How Can it be Done?
I've never attempted to convert a welder to a battery charger before, and I'm not sure if anyone else has either. However - my initial thoughts are as follows (feedback welcome).
1. Measure the voltage & current waveforms from the welder when you simply connect it to a 12 V battery array, set the current limit low and fire (hopefully we get a nice ~12 V current controlled power supply with no spurious voltages and currents on start up. And that it does actually start up)
2. Work out how the welder current control knob on the front panel works and design an interface to it (potentiometer, rotary encoder etc). Include read-back of set current if required.
3. Connect the welder current control knob interface to either an arduino which will manage the charge profile, or use an OTS part such as bq24450 to handle the control. I prefer the bq24450 option as this has all the smarts required a for pre, float and boost charging including ambient temperature adjustments... even though it will take some thinking about how to interface it to the proposed system.
4. Take high current shunt feedback from within welder or external device to the controller
5. Think about safety system (bimetallic thermal cut-outs, overcurrent, overvoltage, etc)
This also sounds like a really fun project for me to get my teeth stuck in to - so much so I may make a YouTube video for my channel on how I built (or failed to build) this absolute monster of a battery charger.
Dan
I have a pretty mad idea to build a super high current lead acid battery charging system on the cheap, using a TIG welder as the power source. Yes, this is potentially very dangerous. So lets get down to the engineering.
Intro
I've recently aquired 11x 92 Ah 12 V batteries that I will be using in a UPS backup system of my own design, all of which will be connected in parallel for charging and discharging. Clearly this battery bank requires a significant charging current - 0.08 to 0.1 C is recommended for a "slow" charge, equating to a charge current of 80.96 A to 101.2 A. Lead acid's require a CV / CC combination to charge correctly, meaning I need excellent control of the output of the TIG welder if this project is going to be possible.
Why Parallel Batteries?
It's a lot easier to find high power (3000 W) 12 VDC to 230 VAC inverters than it is ones that accept 130 / 140 VDC inputs. Additionally, it's easier to charge a bank of parallel 12V lead acids than a series stack (balancing for example).
Why a TIG welder?
There are not many sources of such high current power available to the domestic market for a price that is anything like reasonable. However, due to the magic of globalisation and economies of large-scale manufacturing, we can purchase high current TIG welders for a very reasonable price (for example £130 for a 140 A IGBT variant on Amazon - less than £1 per amp!!). On the face of it, these machines are very nicely suited:
- Current: 10 - 140 A
- No Load Voltage: 56 V
- Rated Output Voltage: 25.6 V
- Efficient
How Can it be Done?
I've never attempted to convert a welder to a battery charger before, and I'm not sure if anyone else has either. However - my initial thoughts are as follows (feedback welcome).
1. Measure the voltage & current waveforms from the welder when you simply connect it to a 12 V battery array, set the current limit low and fire (hopefully we get a nice ~12 V current controlled power supply with no spurious voltages and currents on start up. And that it does actually start up)
2. Work out how the welder current control knob on the front panel works and design an interface to it (potentiometer, rotary encoder etc). Include read-back of set current if required.
3. Connect the welder current control knob interface to either an arduino which will manage the charge profile, or use an OTS part such as bq24450 to handle the control. I prefer the bq24450 option as this has all the smarts required a for pre, float and boost charging including ambient temperature adjustments... even though it will take some thinking about how to interface it to the proposed system.
4. Take high current shunt feedback from within welder or external device to the controller
5. Think about safety system (bimetallic thermal cut-outs, overcurrent, overvoltage, etc)
This also sounds like a really fun project for me to get my teeth stuck in to - so much so I may make a YouTube video for my channel on how I built (or failed to build) this absolute monster of a battery charger.
Dan
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