400 Watt boosting solar charge controller

There is an interesting boost converter style of solar charge controller that I have seen a number of people use and I had been wanting to test this out for a while. The brand is Elejoy (although I see some for sale with the brand name removed) model number: EL-MU400SP. The 400 meaning 400 (ish) watts of power with 200W and 300W versions also available. Since the price tends to fluctuate wildly at times and the higher power model is often not significantly more expensive, I went for the high power handling model.

To give a good idea of what I have, here is a page from the Grin Technologies Ebike website:

https://ebikes.ca/shop/electric-bicycle-parts/solar/adjustable-400w-boost-mppt.html

I need to point out first that this is a boost converter, meaning it takes a certain voltage input and bumps up the output voltage. Because of the way this operates, you need to have at least a couple of volts difference between the input and output. If the voltage of the solar panel is 23V, then the output would need to be set at ~25V or above. I believe it has protection to stop it from attempting to charge when the voltages get too close, but I haven't exercised that part of the device yet. In the future I will go over the manual and some of the finer details of how this thing operates.

I picked up a pair of 100 watt panels for under $120 and can use them in parallel with my 36V nominal battery (42V fully charged, or commonly referred to as 40V for tool batteries). If I move up to a 48V or 52V system, I could put the panels in series. This would allow for lower current at the same given power, which means less voltage drop between the panel and the charge controller. Given that it boosts the voltage, if you need to have a longer run of wire for whatever reason it might be better to lengthen the output side of things. That being said, you also want to protect this from rain or being overheated by the sun, so having the option to use a higher input voltage can certainly be useful.

There is another important point I want to bring up about boost converters. The way they operate is to charge an inductor and then shut off the charge. This causes the inductor to deplete itself as fast as it can, causing a reverse voltage spike. The circuit controls how fast it can charge and deplete. Since it is made for solar panels with blocking diodes, this works fine. I saw some online threads and YouTube comments of people attaching their boost convert to a bench power supply and destroying the power supply, or to a battery for the input and having issues. Myself and a number of other people have had no issues using a solar panel for input as intended, so I would strongly recommend using it with solar only. I'm putting this here both to save anyone down the road some grief, as well as to address anyone who does a search and sees someone claiming to have X years experience and are upset they let the magic smoke out of an expensive power supply.

One last important quirk to mention is that this (and likely other) boost converter style charge controllers are powered by the solar panel. If solar isn't connected, or doesn't have sufficient power to operate the controller then it will shut off. It isn't powered by the battery, so it isn't broken if it fails to light up when a battery is connected to the output. It holds the settings so when solar power resumes it can pick up where it left off.

I will have to come back to this another time and go over more details, but my favorite feature is being able to dial in the voltage. I have always been a fan of not pushing my cells to the extremes of 100% or under 20% charge when I can. I have to charge all the way to top balance the cells occasionally, but not every single time. This has been a huge problem with my wall chargers, as they have no built in way to stop charging where I want them. I have also had issues with them cutting out before the BMS could balance the cells and the first pack I built had one cell drift a fair bit away from the rest. This is a huge topic that I will have to dive in to another time, but I can choose to stop it around 80% or I can measure the voltage at the cell and perhaps dial in 42.2V or 42.3V to make up for the voltage drop and get a full balance charge. Even if the cells reach 4.23 volts a couple times a year, it wouldn't be overcharged to the point of being dangerous, and the lower charge between balancing will greatly extend the battery life. I have had great luck with used cells in the packs I built and little loss of capacity after years and a few thousand miles on them. This charge controller can help me step up my charging game and further extend the life of my batteries while using the sun for power.

The knock-off Wago connector on the one side immediately broke, which worked out fine since I wanted to add a fuse and XT-60 connector. On the input I have a wire with MC-4 connectors to attach to the solar panels. On the output side I made a crude connection, but it works. The blue tape has electrical tape and soldered wires underneath. Heat makes the electrical tape adhesive ooze out and come unraveled, and I find the blue tape holds up much better when I need a quick semi-permanent fix.

Daniel Schmidt wrote:There is an interesting boost converter style of solar charge controller that I have seen a number of people use and I had been wanting to test this out for a while. The brand is Elejoy (although I see some for sale with the brand name removed) model number: EL-MU400SP. The 400 meaning 400 (ish) watts of power with 200W and 300W versions also available. Since the price tends to fluctuate wildly at times and the higher power model is often not significantly more expensive, I went for the high power handling model.

To give a good idea of what I have, here is a page from the Grin Technologies Ebike website:

https://ebikes.ca/shop/electric-bicycle-parts/solar/adjustable-400w-boost-mppt.html

I need to point out first that this is a boost converter, meaning it takes a certain voltage input and bumps up the output voltage. Because of the way this operates, you need to have at least a couple of volts difference between the input and output. If the voltage of the solar panel is 23V, then the output would need to be set at ~25V or above. I believe it has protection to stop it from attempting to charge when the voltages get too close, but I haven't exercised that part of the device yet. In the future I will go over the manual and some of the finer details of how this thing operates.

I picked up a pair of 100 watt panels for under $120 and can use them in parallel with my 36V nominal battery (42V fully charged, or commonly referred to as 40V for tool batteries). If I move up to a 48V or 52V system, I could put the panels in series. This would allow for lower current at the same given power, which means less voltage drop between the panel and the charge controller. Given that it boosts the voltage, if you need to have a longer run of wire for whatever reason it might be better to lengthen the output side of things. That being said, you also want to protect this from rain or being overheated by the sun, so having the option to use a higher input voltage can certainly be useful.

There is another important point I want to bring up about boost converters. The way they operate is to charge an inductor and then shut off the charge. This causes the inductor to deplete itself as fast as it can, causing a reverse voltage spike. The circuit controls how fast it can charge and deplete. Since it is made for solar panels with blocking diodes, this works fine. I saw some online threads and YouTube comments of people attaching their boost convert to a bench power supply and destroying the power supply, or to a battery for the input and having issues. Myself and a number of other people have had no issues using a solar panel for input as intended, so I would strongly recommend using it with solar only. I'm putting this here both to save anyone down the road some grief, as well as to address anyone who does a search and sees someone claiming to have X years experience and are upset they let the magic smoke out of an expensive power supply.

One last important quirk to mention is that this (and likely other) boost converter style charge controllers are powered by the solar panel. If solar isn't connected, or doesn't have sufficient power to operate the controller then it will shut off. It isn't powered by the battery, so it isn't broken if it fails to light up when a battery is connected to the output. It holds the settings so when solar power resumes it can pick up where it left off.

I will have to come back to this another time and go over more details, but my favorite feature is being able to dial in the voltage. I have always been a fan of not pushing my cells to the extremes of 100% or under 20% charge when I can. I have to charge all the way to top balance the cells occasionally, but not every single time. This has been a huge problem with my wall chargers, as they have no built in way to stop charging where I want them. I have also had issues with them cutting out before the BMS could balance the cells and the first pack I built had one cell drift a fair bit away from the rest. This is a huge topic that I will have to dive in to another time, but I can choose to stop it around 80% or I can measure the voltage at the cell and perhaps dial in 42.2V or 42.3V to make up for the voltage drop and get a full balance charge. Even if the cells reach 4.23 volts a couple times a year, it wouldn't be overcharged to the point of being dangerous, and the lower charge between balancing will greatly extend the battery life. I have had great luck with used cells in the packs I built and little loss of capacity after years and a few thousand miles on them. This charge controller can help me step up my charging game and further extend the life of my batteries while using the sun for power.

The knock-off Wago connector on the one side immediately broke, which worked out fine since I wanted to add a fuse and XT-60 connector. On the input I have a wire with MC-4 connectors to attach to the solar panels. On the output side I made a crude connection, but it works. The blue tape has electrical tape and soldered wires underneath. Heat makes the electrical tape adhesive ooze out and come unraveled, and I find the blue tape holds up much better when I need a quick semi-permanent fix.

a nice appropriate size project! Hope you post results as you explore the possibilities.
Cheers, David

Thank you! I know there are some quirks and a few things about the manual that don't seem to line up, but it's been working well for me. My posts tend to get very long-winded, and I do that in hopes that people who come across them through searches can have as many details as I can give. I'm going to gather more notes about the setup and organize them into slightly more digestible chunks.

Sadly with all of the different connectors and proprietary setups, it likely won't be 'plug and play' to connect this to just any ebike. It can be made to work in a lot of cases if you are determined enough. I currently have XT-60 connectors on all of my 36V batteries, and will likely move up to XT-90 connectors for higher voltage packs to avoid any mistakes, as well as making use of the higher current handling capacity.

I'm hoping to eventually get to a point where I have a 48V electric trike that doubles as a power source using an inverter. As an individual who has spent a lot of time minimizing my personal power consumption, it's usually the occasional task requiring a bunch of power tool usage that eats up more energy than almost anything else in my life. For me it makes a lot of sense to have a cargo trike with an oversized battery that can occasionally haul stuff, go on a longer trek, or act as a power source that I can roll wherever I need it. With it being a secondary form of transportation, it can sit around for a few days and charge up slowly. As I keep moving forward I will update things and make more threads to show what I have going on. There are lots of ways of going about using ebikes and solar power. My successes can probably help other people with their goals, and maybe it can spark a few ideas that can be shared back to the community.

Daniel Schmidt wrote:Thank you! I know there are some quirks and a few things about the manual that don't seem to line up, but it's been working well for me. My posts tend to get very long-winded, and I do that in hopes that people who come across them through searches can have as many details as I can give. I'm going to gather more notes about the setup and organize them into slightly more digestible chunks.

Sadly with all of the different connectors and proprietary setups, it likely won't be 'plug and play' to connect this to just any ebike. It can be made to work in a lot of cases if you are determined enough. I currently have XT-60 connectors on all of my 36V batteries, and will likely move up to XT-90 connectors for higher voltage packs to avoid any mistakes, as well as making use of the higher current handling capacity.

I'm hoping to eventually get to a point where I have a 48V electric trike that doubles as a power source using an inverter. As an individual who has spent a lot of time minimizing my personal power consumption, it's usually the occasional task requiring a bunch of power tool usage that eats up more energy than almost anything else in my life. For me it makes a lot of sense to have a cargo trike with an oversized battery that can occasionally haul stuff, go on a longer trek, or act as a power source that I can roll wherever I need it. With it being a secondary form of transportation, it can sit around for a few days and charge up slowly. As I keep moving forward I will update things and make more threads to show what I have going on. There are lots of ways of going about using ebikes and solar power. My successes can probably help other people with their goals, and maybe it can spark a few ideas that can be shared back to the community.

you might wan to consider a voltage converter to step down the trike voltage to 12 volt. There are a lot of cheap options in the small 12 volt inverter range.  Small 48 volt gear is limited and more expensive. Just a thought. Enjoy.
cheers, David