40A Smart Mains Battery Charger for under £15?
- Thread starter wildebus
- Start date
wildebus
Forum Member
The typical 40A Smart Mains Charger can run at over £200. If you have either a B2B Charger or a good Solar Charger, you can get all the functions of a Smart Charger when plugged into the mains without the expense of getting another Smart Device 
By switching the input from the Starter Battery/Alternator (in the case of the B2B) or from the PV Solar Panel (for the Solar Charger) and feeding it from a simple mains power supply, you can get the same functionality at a fraction of the cost
This is my test setup. In this case I am using a a 400W Power Supply with a 48VDC/8.3A output (so maximum output would be around 35A at 12V) and feeding it into a Victron MPPT 100/20 Smart Controller (so actually limited to 20A maximum output)
PSU + MPPT by David, on Flickr
I could have bought just a 300W PSU and with a 24V output as well for example - what is best depends on the Solar Controller specification (I got the one I did so I could use it on 24V Leisure Battery systems and with bigger MPPTs)
Switching it on, I am putting the near maximum output from the Controller into the Battery Bank
MPPT Input and Output by David, on Flickr
If you already had this MPPT Controller, the cost of adapting it to become a AC Smart Charger would be just a cost of a PSU and either a switch or a relay. This is the PSU in the photo above - https://amzn.to/2Q9NIZ8 - for just £13.
If you wanted to do similar with a B2B you would need to feed it with an DC voltage around 14V or so, but the same principle would apply (exactly the same as my B2B testing did). The Solar Controller method is a lot more flexible I would say as the voltage range is typically a lot more flexible and needs a lot less regulation
PS. As usual, trying this is at your own risk and if trying this, ensure the PSU output does not exceed any voltage or current limitations of the Solar Controller (or B2B).
By switching the input from the Starter Battery/Alternator (in the case of the B2B) or from the PV Solar Panel (for the Solar Charger) and feeding it from a simple mains power supply, you can get the same functionality at a fraction of the cost
This is my test setup. In this case I am using a a 400W Power Supply with a 48VDC/8.3A output (so maximum output would be around 35A at 12V) and feeding it into a Victron MPPT 100/20 Smart Controller (so actually limited to 20A maximum output)
PSU + MPPT by David, on Flickr
I could have bought just a 300W PSU and with a 24V output as well for example - what is best depends on the Solar Controller specification (I got the one I did so I could use it on 24V Leisure Battery systems and with bigger MPPTs)
Switching it on, I am putting the near maximum output from the Controller into the Battery Bank
MPPT Input and Output by David, on Flickr
If you already had this MPPT Controller, the cost of adapting it to become a AC Smart Charger would be just a cost of a PSU and either a switch or a relay. This is the PSU in the photo above - https://amzn.to/2Q9NIZ8 - for just £13.
If you wanted to do similar with a B2B you would need to feed it with an DC voltage around 14V or so, but the same principle would apply (exactly the same as my B2B testing did). The Solar Controller method is a lot more flexible I would say as the voltage range is typically a lot more flexible and needs a lot less regulation
PS. As usual, trying this is at your own risk and if trying this, ensure the PSU output does not exceed any voltage or current limitations of the Solar Controller (or B2B).
Last edited:
smdts
That is a great idea, adding the relay. I did similar a while ago as I needed a cheap way to charge a 72v forklift so I used 3 40a cheap chinese solar charge controllers and 3 40a power supplies.
do you need to manually trigger the relay or are you using a double throw relay powered off the psu for an automatic changeover from solar to mains?
do you need to manually trigger the relay or are you using a double throw relay powered off the psu for an automatic changeover from solar to mains?
wildebus
Forum Member
This was more of a proof of concept to demonstrate the principle. Not actually installed this full-time
For low-current (30A or less) I would use a 5-pin relay on the +ve feeds. If bigger, then probably a manual 2-way high-current switch like this for example - https://amzn.to/34NU2sz
Either way would probably switch it manually between the two inputs, but it would not be very hard to have it auto-switching.
wildebus
Forum Member
My method is cheaper and more flexible
PS. If that charger is putting out 40A, I hope you have a fire extinquisher ready. those DC leads look just a touch on the light side
smdts
those 40a chargers on ebay are £88 now, unless i am missing a trick?
also anything that comes with those fuseless plugs I dont feel comfortable leaving powered up unsupervised, If they are pennypinching on a fused plug, what other nasties are going on inside the casing, what is the primary-secondary isolation like, when I worked in a power supply design lab as a tech we reverse engineered a lot of chinese power supplies that faked our branding but had deathtraps inside, to the point where the failure of a single already underspecced swmiconductor would result in 240v at the 24v output terminals.
also anything that comes with those fuseless plugs I dont feel comfortable leaving powered up unsupervised, If they are pennypinching on a fused plug, what other nasties are going on inside the casing, what is the primary-secondary isolation like, when I worked in a power supply design lab as a tech we reverse engineered a lot of chinese power supplies that faked our branding but had deathtraps inside, to the point where the failure of a single already underspecced swmiconductor would result in 240v at the 24v output terminals.
voyager
Forum Member
That's the way I went after reading comments from others that had done the same thing.The typical 40A Smart Mains Charger can run at over £200. If you have either a B2B Charger or a good Solar Charger, you can get all the functions of a Smart Charger when plugged into the mains without the expense of getting another Smart Device
By switching the input from the Starter Battery/Alternator (in the case of the B2B) or from the PV Solar Panel (for the Solar Charger) and feeding it from a simple mains power supply, you can get the same functionality at a fraction of the cost
This is my test setup. In this case I am using a a 400W Power Supply with a 48VDC/8.3A output (so maximum output would be around 35A at 12V) and feeding it into a Victron MPPT 100/20 Smart Controller (so actually limited to 20A maximum output)
PSU + MPPT by David, on Flickr
I could have bought just a 300W PSU and with a 24V output as well for example - what is best depends on the Solar Controller specification (I got the one I did so I could use it on 24V Leisure Battery systems and with bigger MPPTs)
Switching it on, I am putting the near maximum output from the Controller into the Battery Bank
MPPT Input and Output by David, on Flickr
If you already had this MPPT Controller, the cost of adapting it to become a AC Smart Charger would be just a cost of a PSU and either a switch or a relay. This is the PSU in the photo above - https://amzn.to/2Q9NIZ8 - for just £13.
If you wanted to do similar with a B2B you would need to feed it with an DC voltage around 14V or so, but the same principle would apply (exactly the same as my B2B testing did). The Solar Controller method is a lot more flexible I would say as the voltage range is typically a lot more flexible and needs a lot less regulation
PS. As usual, trying this is at your own risk and if trying this, ensure the PSU output does not exceed any voltage or current limitations of the Solar Controller (or B2B).
wildebus
Forum Member
Just for a comparison, this afternoon I turned on the basic 240VAC/48VDC PSU for 30 minutes, running through the MPPT Controller as described. Then turned it off and turned on my normal regular mains Charger (a Victron 120A Multiplus).
Apart from the dip in the middle which is the point where the PSU was turned off before the Multiplus was turned on, you cannot tell the difference in the charging profile - a gradually declining current as the battery bank SOC% is increasing.
This is really just a confirmation that the approach I discussed in the first post is just as reliable as getting a conventional smart mains charger.
Apart from the dip in the middle which is the point where the PSU was turned off before the Multiplus was turned on, you cannot tell the difference in the charging profile - a gradually declining current as the battery bank SOC% is increasing.
This is really just a confirmation that the approach I discussed in the first post is just as reliable as getting a conventional smart mains charger.
trevskoda
Forum Member
Mine has a fuse and works 100%,i do see a price rise on some,i was lucky at 20 bucks,yes there is crap out there but stuff in shops here is crap to these days,prob all from china but cannot blame every thing made there.