How to charge a 12V battery from a 24V battery. Uses a buck converter and a couple of voltage controlled relays. Modules used: XH-M604, XY-CD63L, Ming He B3008
Not sure I see the point of the relay closest to the target battery since the current limiting module will simply, with the right voltage setting, charge the battery whenever the supply relay is on. Adding a zener diode to the target battery terminal will prevent the battery from back feeding the current limiter. Fewer modules, fewer points of failure and less parasitic drain when charging is not taking place...
Can't help but admire the convoluted nature of this. Probably needlessly complex, but far more interesting than a little black box that does it all inconspicuously. Do feel like I'd want something to prevent the backfeed though, and I'm not really sure where I'd put the buck converter in the chain. I'd also stick a manual switch or two on there to disconnect either side from the circuit and for extra gadgetyness. Would be nice to see the final setup in action, perhaps another shed tour in due course?
LiFePo4 batteries have a built-in BMS. At 14.6 volts the BMS disconnects the charging Mosfet and at 10 volts the BMS disconnects the discharging Mosfet. You only need a step down regulator to 14.6V and 10A
Right, I was thinking that too although there’s a huge range of BMSs around these days, including many that I probably wouldn’t trust to handle the in/out limits for this situation. Any quality BMS with user controlled settings and an app for monitoring could handle all that switching reliably I would think
Heh, when you get this all finished, people won't see you for days and wonder what happened, only to shockingly discover that you are trapped in your own spider web made of wires. ;)
same transition from 24 to 12 for me and all my panels are 35+volts . you can use dc clock switch to open your charge via sun 4-5 hours only in daytime.. only thing is some converters love to have first the input then the load... or mine just kicked with a big ark when charged backwards
I'd put a diode after the buck converter then go to the battery instead. Not using the one module after the buck converter, as it is not needed. Stopping the battery backfeeding in the process too.
I'm really interested in the plethora of bidirectional USB power delivery boards on Ali and the newer chips from Linear Technologies that supposedly handle almost every facet of true MPPT for you across a wide range of voltages. Might incorporate them into my first PCB design ever (despite the price).
YES! These! I’ve been eyeing some of those bi-directional PD/ QC boards as well, waiting for the price to come down. I imagine them being quite useful! Those power delivery protocols are widening the list of available voltage and current options but currently it’s 3.3v to 24v 100w+, 200W right around the corner. There’s ones that buck/boost to achieve that output whether the input be 5v or 32v I think. I use a lot of the 1 way PD boards for charging devices and powering LEDs but the 2-way boards seem like a new level of awesomeness.
I have two battery system in use in my garage, 12 and 24v too. To recharge the 12v system i just use another epever tracer and instead feeding in solar i just connect it to the load out of my main charge controller. That way i can program the load out to only be enabled when charge is high enough and i have a second load out on the 12v side which i can then use to control my 12v loads. It works just fine for almost a year now. There's no backfeeding or other problems and the stand-by current draw of the charge controllers is really low. All these relays and controllers seems to be way over complicated.
@@JulianIlett haha, okay, i accept that answer. making the unusual solutions work is quite fun 😁 As an electrician specialized in electronics, i can totally understand that. If function is just the 2nd priority, then trying thing out is perfectly fine 👍
never seen the point of wanting to work in a shed in the UK! For a few days of the year it's too hot and the rest of the year its wet and cold, or cold, or just wet. plus all my tools go rusty in the shed. 😞 I'll stick with working in my toy room 🙂warm, dry and loads of mains power. I think you need to start to look at a processor controlled switching matrix so you can balance all the incoming power to your storage requirements.
@@JulianIlett🙂My toy room is meant to be the 4th bedroom. but being big enough to be a bedroom is only in the mind of an estate agent. As long as I leave a path to the airing cupboard I'm normally ok with all the toys 🙂
We had 4 bedrooms when we lived in Hayes, but lost a bedroom when we moved to High Wycombe. We gained a study (my workshop), but it's tiny. The shed does have its challenges, but overcoming them keeps my brain active :)
@@JulianIlett Not been to High Wycombe in years. the Hellfire caves was a fun place to visit, only about 20 miles from where we used to live. I've got to build a shed for the other half to replace the old one that's falling down. so it might be a modular shed 🙂
You need thicker cables to prevent the voltage drop. I am using 2.5mm multi strand wire, doubled up to equal 5mm square, it still solders into the ring terminals with a bit of manipulation. QUESTION: Can you please drop me a link for your source of Banana plugs.? I can only find unshielded decent Speaker type ones, which are no good with high current sources, in case of accidental shorts ETC. Even plugged in they are unshielded.
There is a small voltage drop in the cables, but it's only a few tens of millivolts. The banana plugs came from either Rapid Electronics or CPC Farnell, but the last time I looked they had been discontinued.
interesting. i also did something like that for my own "ups" psu at 14V feeds into relay when feeds converter to keep V at 12.4V when psu is off relays goes off and switches other relay on which reconnects battery which is off when psu is on to charge the battery. a little relay circuit that suppose to switch between psu and battery to power something, but it doesnt charge battery.
U can't use a battery while charging at low current unless you power the devices with the charger assuming you mean 1 battery best have 1 battery charging 1 battery in use
There is a simpler and easier way to do this. You know those little "solar" "MPPT" buck converters? They have a third pot on them, so not only do they give you configurable output charge voltage and current limit, they also set you set the minimum input voltage from the source below which they will not draw any more power. No need for relays. The only other component you might need is a diode to prevent backfeed from the destination battery into the buck converter.
Do you have a link for buying or at least looking at these devices specs ? When I enter "give take energy" in aliexpress, I mostly get testoterone boosters proposed :)
This is crying out for a bespoke home made solution, maybe even including an ESP32 with WiFi broadcasting voltages etc. Common Julian, give us a circuit diagram and build series. 😀
Seems like a complicated way to do bugger-all. Too many boards drawing too much current to be efficient. I use a ZK-J5X V3 to charge a 12V pack from my main 24V pack.
@@JulianIlett ya, like cars have that to v2g. There’s amp and volt measurements on both sides and a full bridge on them so that they can buck based on parameters and boost in the opposite case. V2g just pushes more voltage back up from the battery OR pulls depending on mode but it could be automatic.
Great to see that contraption all working together with a knackered battery , shows the full functionality of the principal.
Not sure I see the point of the relay closest to the target battery since the current limiting module will simply, with the right voltage setting, charge the battery whenever the supply relay is on. Adding a zener diode to the target battery terminal will prevent the battery from back feeding the current limiter. Fewer modules, fewer points of failure and less parasitic drain when charging is not taking place...
I do see your point. All I'd lose is the hysteresis on the destination battery and I can't immediately think how that would be a problem.
Can't help but admire the convoluted nature of this. Probably needlessly complex, but far more interesting than a little black box that does it all inconspicuously. Do feel like I'd want something to prevent the backfeed though, and I'm not really sure where I'd put the buck converter in the chain. I'd also stick a manual switch or two on there to disconnect either side from the circuit and for extra gadgetyness. Would be nice to see the final setup in action, perhaps another shed tour in due course?
There's a manual switch of sorts on the LCD relay unit. Pressing the bottom button puts it in an off state.
It's now all set up and working in the shed so I'll make an update video soon.
LiFePo4 batteries have a built-in BMS.
At 14.6 volts the BMS disconnects the charging Mosfet and at 10 volts the BMS disconnects the discharging Mosfet.
You only need a step down regulator to 14.6V and 10A
Right, I was thinking that too although there’s a huge range of BMSs around these days, including many that I probably wouldn’t trust to handle the in/out limits for this situation. Any quality BMS with user controlled settings and an app for monitoring could handle all that switching reliably I would think
I just wonder isn’t there an all in one solution to achieve this? Would work better together and surely more efficient.
I use 60x60cm led panels for lighting in my shed. They give a much better light spread than tubes.
Heh, when you get this all finished, people won't see you for days and wonder what happened, only to shockingly discover that you are trapped in your own spider web made of wires. ;)
Add to that the actual spider's webs and you're about right :)
same transition from 24 to 12 for me and all my panels are 35+volts . you can use dc clock switch to open your charge via sun 4-5 hours only in daytime.. only thing is some converters love to have first the input then the load... or mine just kicked with a big ark when charged backwards
I'd put a diode after the buck converter then go to the battery instead. Not using the one module after the buck converter, as it is not needed. Stopping the battery backfeeding in the process too.
I'm really interested in the plethora of bidirectional USB power delivery boards on Ali and the newer chips from Linear Technologies that supposedly handle almost every facet of true MPPT for you across a wide range of voltages. Might incorporate them into my first PCB design ever (despite the price).
YES! These! I’ve been eyeing some of those bi-directional PD/ QC boards as well, waiting for the price to come down. I imagine them being quite useful! Those power delivery protocols are widening the list of available voltage and current options but currently it’s 3.3v to 24v 100w+, 200W right around the corner. There’s ones that buck/boost to achieve that output whether the input be 5v or 32v I think. I use a lot of the 1 way PD boards for charging devices and powering LEDs but the 2-way boards seem like a new level of awesomeness.
Must be great to have so much free stuff and invent some complex use for it.
Some stuff is free, but the rest I have to pay for.
put a ideal diode from the step down to the second "charge controller" and jo have no reverse current flow.
Great video. It's a shame you can't buy an all in one bidirectional buck converter. 😊
I have two battery system in use in my garage, 12 and 24v too. To recharge the 12v system i just use another epever tracer and instead feeding in solar i just connect it to the load out of my main charge controller. That way i can program the load out to only be enabled when charge is high enough and i have a second load out on the 12v side which i can then use to control my 12v loads.
It works just fine for almost a year now. There's no backfeeding or other problems and the stand-by current draw of the charge controllers is really low.
All these relays and controllers seems to be way over complicated.
I'm trying to do this without using charge controllers. It's challenging (but fun) trying to get it all to work.
@@JulianIlett haha, okay, i accept that answer. making the unusual solutions work is quite fun 😁 As an electrician specialized in electronics, i can totally understand that. If function is just the 2nd priority, then trying thing out is perfectly fine 👍
Nice but would a relay or diode stop the back charge of the buck convertor????
The backfeed through the buck converter isn't a problem. As long as it's understood why it's happening.
never seen the point of wanting to work in a shed in the UK! For a few days of the year it's too hot and the rest of the year its wet and cold, or cold, or just wet. plus all my tools go rusty in the shed. 😞
I'll stick with working in my toy room 🙂warm, dry and loads of mains power.
I think you need to start to look at a processor controlled switching matrix so you can balance all the incoming power to your storage requirements.
Working in the shed is not a want, it's a need. My office has a smaller footprint than my car!
@@JulianIlett🙂My toy room is meant to be the 4th bedroom. but being big enough to be a bedroom is only in the mind of an estate agent. As long as I leave a path to the airing cupboard I'm normally ok with all the toys 🙂
We had 4 bedrooms when we lived in Hayes, but lost a bedroom when we moved to High Wycombe. We gained a study (my workshop), but it's tiny. The shed does have its challenges, but overcoming them keeps my brain active :)
@@JulianIlett Not been to High Wycombe in years. the Hellfire caves was a fun place to visit, only about 20 miles from where we used to live.
I've got to build a shed for the other half to replace the old one that's falling down. so it might be a modular shed 🙂
You need thicker cables to prevent the voltage drop. I am using 2.5mm multi strand wire, doubled up to equal 5mm square, it still solders into the ring terminals with a bit of manipulation.
QUESTION:
Can you please drop me a link for your source of Banana plugs.? I can only find unshielded decent Speaker type ones, which are no good with high current sources, in case of accidental shorts ETC. Even plugged in they are unshielded.
There is a small voltage drop in the cables, but it's only a few tens of millivolts. The banana plugs came from either Rapid Electronics or CPC Farnell, but the last time I looked they had been discontinued.
interesting. i also did something like that for my own "ups" psu at 14V feeds into relay when feeds converter to keep V at 12.4V when psu is off relays goes off and switches other relay on which reconnects battery which is off when psu is on to charge the battery. a little relay circuit that suppose to switch between psu and battery to power something, but it doesnt charge battery.
U can't use a battery while charging at low current unless you power the devices with the charger assuming you mean 1 battery best have 1 battery charging 1 battery in use
There is a simpler and easier way to do this. You know those little "solar" "MPPT" buck converters? They have a third pot on them, so not only do they give you configurable output charge voltage and current limit, they also set you set the minimum input voltage from the source below which they will not draw any more power. No need for relays. The only other component you might need is a diode to prevent backfeed from the destination battery into the buck converter.
is charge controller the right search term for those controllers with upper and lower set points?
Best to search using the module model numbers.
Thank you. @@JulianIlett
Do you have a link for buying or at least looking at these devices specs ?
When I enter "give take energy" in aliexpress, I mostly get testoterone boosters proposed :)
Modules used: XH-M604, XY-CD63L, Ming He B3008
This is crying out for a bespoke home made solution, maybe even including an ESP32 with WiFi broadcasting voltages etc. Common Julian, give us a circuit diagram and build series. 😀
A modular build suits my aging eyes and hands. A software-less approach suits my waning mental dexterity.
@@JulianIlett That's what ChatGPT is for. 😉
Looks to me like a fire waiting to happen
Seems like a complicated way to do bugger-all. Too many boards drawing too much current to be efficient. I use a ZK-J5X V3 to charge a 12V pack from my main 24V pack.
Why not just use a push/pull buck/boost and set limits in it?
push pull buck boost?
@@JulianIlett ya, like cars have that to v2g. There’s amp and volt measurements on both sides and a full bridge on them so that they can buck based on parameters and boost in the opposite case.
V2g just pushes more voltage back up from the battery OR pulls depending on mode but it could be automatic.
Oh OK. I've seen some Linear Technology IC's that can do that, but I've not seen any modules for sale yet.
@@JulianIlett get out the wood board and make one please! Would love to see you build one with an arduino!