diy solar

diy solar

Benchtop Power Supply for under $100.

In the description on that page you linked, I found the words:


IMO, if you aren't comfortable with adjustable benchtop supplies, using them as a charger isn't a great idea. If you happen to have one, know how to use it, it will work. But it isn't what it was built for. I guess the other reason would be if you need some odd voltage (or too high like 60V) not found in regular Lithium or R/C chargers.

Thank you I will keep a look out for those words in the future. The best idea to check if the machine is working properly, find the voltage of the cell, let's say it is at 3.4. Set the machine to 3.45/3.5, set the CV mode, and see if the amps drop to 0 when it reaches 3.45/3.5 on that one cell? I have trust issues with all mechanical things, I have to test them out to see if they work as advertised. Just like how most home ovens give up after for 4~6 hours of continuous baking at high temperature :censored:. But once I understand how they work, I will know which boundaries not to cross so I can keep on using things for the longest time.

I just don't understand how the concepts work on the machine itself. Will the bench supply automatically take care of it? We set CV, set the voltage at 3.65, have another volt meter checking the battery side, just to be safe. Once the voltage hits 3.65, the bench supply will start reducing the amps on its own until it reaches down to zero (simplified version in my brain on how it is suppose to work)?

Hopefully once I have the cells in my hands, I can ask more relevant questions on how to get stuff done actually, rather than just thinking about it.

It is not a matter of if I am comfortable or not, some things you just have to learn and get used to them in your own way. Later down the road, we can all laugh at the little fears we had when we started (y). Otherwise life has a way of rubbing our nose in the things we avoid.
 
Set the machine to 3.45/3.5, set the CV mode, and see if the amps drop to 0 when it reaches 3.45/3.5 on that one cell
Actually the process is you set the CV value first. If that voltage is above the voltage of the cells then it automatically goes into CC mode giving it as much current as the setting or its capacity will allow. When the voltage of the cells equals the max voltage setting, the power supply ramps down the current to maintain the voltage at the setting. The voltage stays the same (CV) as the current ramps down. I think we agree conceptually on how it works. My detailed explanation is for the benefit of other readers.
 
Actually the process is you set the CV value first. If that voltage is above the voltage of the cells then it automatically goes into CC mode giving it as much current as the setting or its capacity will allow. When the voltage of the cells equals the max voltage setting, the power supply ramps down the current to maintain the voltage at the setting. The voltage stays the same (CV) as the current ramps down. I think we agree conceptually on how it works. My detailed explanation is for the benefit of other readers.

Thank you, that makes a whole lot more sense to me now :geek:.
 
It is not a matter of if I am comfortable or not, some things you just have to learn and get used to them in your own way. Later down the road, we can all laugh at the little fears we had when we started (y). Otherwise life has a way of rubbing our nose in the things we avoid.

Ok, now I understand! I'm the same way. If your goal is to learn and tinker with things, then an adjustable supply will be useful. I bought mine basically for one project and have used it for all sorts of things.

I posted earlier in this thread about how a dedicated charger does CC then CV modes. I'll expand on that here to try and help with your questions. The following is true for my adjustable PSU, and likely most of them, but I'm not 100% sure of that.

The PSU has two limits I can adjust. Current and Volts. Both limits are enforced all the time, allowing for some slop and a bit of time delay. The PSU does have two modes, constant voltage and constant current. It switches between from CV to CC whenever the current limit is hit. Once the load is drawing less than the current limit, it automatically switched back to CV mode.

Some examples: In both of these, let's pretend the resistance feeding the battery is always 0.01Ω and battery is at 4.0V.

Example 1
I set the PSU limits at 4.1V and 15A and connect the PSU to the battery. The voltage difference between PSU and battery is 0.1V, so battery will draw 10A of current. This is below the 15A limit. So the PSU happily supplies 10A at 4.1V to the battery. As the battery charges, its internal voltage increases and so the voltage difference between PSU and battery is less. When the battery is at 4.05V, it will only draw 5A. The PSU isn't adjusting current, it's just a result of the decreasing voltage difference divided by the resistance. The PSU is supplying as much current as the battery draws as long as it is below the 15A limit I set. Eventually the battery will come up to 4.1V and draw no current. But, the PSU will stay on and not let the battery rest.

Example 2
If I set the PSU limits at 4.1V and 2A and connect the PSU to the battery. The voltage difference between PSU and battery is 0.1V, so battery will try to draw 10A of current. If the PSU The PSU will limit this to 1A. How does it do that? By lowering its own voltage until the battery only draws 1A or less. At the start, that means the PSU will lower its voltage to 4.02V. When the battery's voltage gets a little closer to 4.02, the PSU will raise its own voltage (never above the 4.1V limit) just enough so that that 2A or less is delivered to the battery. Eventually, the PSU raises its own voltage to the 4.1V limit I set and it stops there. The PSU switches to Constant Voltage mode automatically. As the battery gets closer to that limit, the current it draws lowers from 2A towards zero.

In the real world things are a bit messier, but this gives the general idea. One thing to be aware of is there is a time delay for the PSU to switch between enforce voltage limit and enforce current limit modes. Your load could draw more current than your set limit during that time. Depending on the load, the PSU and the wires you use to connect them, this could damage something. As an example, If you connect a 3.1V battery with 0.01Ω resistance to a PSU set to 4.1V, that battery is going to try and draw 100A until the PSU can switch modes and lower its own voltage. All these PSUs have a way to force them into CC mode first, if I care about the current limit right away, I just do that.

You'll probably still get more accurate and safer results with an R/C charger. But it definitely won't be as flexible.
 
Once the load is drawing less than the current limit, it automatically switched back to CV mode.
I see the process somewhat differently but I think on a high level we agree. I have to give credit to @smoothJoey for helping me see the subtle difference. I once thought it was the battery that determined the transition.
The way I understand it is that in the CC phase when the battery voltage hits the CV setting the power supply adjusts current to keep the voltage from going higher. That point is the transition from CC to CV.
 
Sort of. A few important things to straighten out

The PSU does not adjust current. The only "tool" the PSU has available to enforce its limits is adjustable voltage. Let's say you short circuit the power supply output + and -. The is close to zero resistance, so nearly infinite current will be drawn from the power supply thru the wire that is connecting + to -. The power supply's only choice is to keep dropping voltage in an effort to meet the current limit. In this case, the PSU will eventually drop to 0V. At 0V no current will flow, 0A is less than whatever limit I can set on the PSU so the current limit is now enforced.

Power sources provide power at some voltage, Power loads (light bulbs, heaters, everything that uses power) draw current from power source. The load "controls" how much current it draws by how much resistance is in the circuit. The power source (an adjustable PSU or the power outlet in my wall) does not control the current directly. A 60W light bulb is built so that so that is has a specific resistance so that when it is plugged into a 120V (I'm in the US) outlet no more than 0.5A (120V x 0.5A = 60W) is drawn from the outlet in my house. It's the overall resistance of the circuit, combined with the voltage, that determines how much current flows.

You are right that batteries don't determine CC/CV transition. When charing a battery, it is just a dumb load like a light bulb.
 
The only "tool" the PSU has available to enforce its limits is adjustable voltage.
Exactly. That was the aha moment that @smoothJoey made me aware of. I think we are on the same page. Hopefully this dialogue will help inform others.
The physics that I alluded to is actually explained by Ohms Law which you explain very well without referring to it. Do I have that correct?
 
Thank you for the explanations @krby . I did get some of it, other went over my head. I will keep on reading the information and researching it. Hopefully over time, I will get a better understanding.

Thanks for confirming the hypothesis @Ampster, helps build the knowledge foundation.
 
I am looking for a low cost Benchtop power supply to charge assembled 12V & 24V LiFePO4 battery banks that have BMS systems installed.
The features I am looking for are:
  • Variable Voltage (Up to 30 V)
  • Variable Current (10 Amp or more)
  • I would like good accuracy (.01V) on the built in volt meter, but I do not plan to push my batteries to 100% charge so I am willing to give this up for price as long as the voltage does not drift.
Note: Since I will be charging batteries that have a BMS already incorporated I do not need a Ballenced Charger like they RC hobbyists use.

I am looking at THIS on amazon (https://smile.amazon.com/Yescom-Precision-Variable-Digital-Adjustable/dp/B00SWK6M0M)
This is obviously a mass produced Chinese knock-off, but sometimes that is good enough. What do others use?
I am using a DPS 5015 module from your favourite chinese supplier and feed the module from 3 old 19V 4A notebook power supplies from the scrapeyard. Anything else providing a fixed DC will do as well. The modules are accurate, damn cheap and display a lot of information. You can also program them over Bluetooth and get charts etc...
The modules cost around 40$ and then it's up to you to buy a dedicated case (15$) or to put it into an industrial cabinet.

DPS5015
Display: 1.44" LCD
Input Voltage: DC 6-60V
Output Voltage: 0-50.00V
Output Current: 0-15.00A
Output Power: 0-750W
 
I am researching benchtop power supplies and LiFePO4 chargers. Ideally, I can purchase one device and do both top balancing as needed and charge the battery bank every now and then when I have 240v mains/shore power available.

I don't need it to function as a power supply for any DC loads except the battery cells and bank - appliances, lights etc are powered by 240v directly when available.

Currently it's a 4S 12v 272Ah LiFePO4 bank (may expand in the future) with a Daly BMS.

I have found a few options:
  1. Ones that look like this, usually 0-30v and 0-5A or 0-10A and very cheap. Seems to be the default budget option.
  2. Riden/RD's RD series, 0-60v RD6006 (6A), RD6012 (12A) or RD6018 (18A), more flexible, faster charging, pretty colours, bluetooth/USB connectivity, firmware updates which appear to actually happen, does not include a PSU (they sell one that is suitable but only 800W vs max capability of 1080W), more expensive. Great intro benchtop power supply, can upgrade with a beefier PSU to handle 48v @ 18A as well.
  3. Riden/RD's DP series, like this one, which have similar features to the RD series and does not include a PSU, but does have a 20A output version. I think I would rather have the RD series with better interface, and live with 2A less current.
  4. This interesting 3-15v 50A unit and its brethren, which appear to consist of a buck converter bolted onto a range of PSUs, with a potentiometer for current and trim pot for voltage. I think it will shut off when current drops to nil - seems like a great way to do top balancing on parallel cells and then also quickly charge a larger battery bank. The 3-15v version also includes a reverse polarity protection thingy to help prevent the loss of magic smoke via a bumbling idiot's hands.
  5. Buy a super cheap buck converter with minimal controls and a cheap Ebay server PSU, rated appropriately. Could build it into a case for something that is easy to move and use. Feels janky though?
  6. Any number of much more expensive but less electrically scary than these cheaper ones.

So, #4 appears to be a pretty good option. I can top balance my cells in parallel and charge the whole bank fairly rapidly.

Or, a #1 and then a dedicated charger that has an LiFePO4 charge profile - something that floats @ 13.6v.

Thoughts? Thank you!
 
I agree the 50 Amp version sounds like a versitile option. I am also lookingvfor someting that can do parallel top balancing in that range of current output.
 
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I am researching benchtop power supplies and LiFePO4 chargers. Ideally, I can purchase one device and do both top balancing as needed and charge the battery bank every now and then when I have 240v mains/shore power available.

I don't need it to function as a power supply for any DC loads except the battery cells and bank - appliances, lights etc are powered by 240v directly when available.

Currently it's a 4S 12v 272Ah LiFePO4 bank (may expand in the future) with a Daly BMS.

I have found a few options:
  1. Ones that look like this, usually 0-30v and 0-5A or 0-10A and very cheap. Seems to be the default budget option.
  2. Riden/RD's RD series, 0-60v RD6006 (6A), RD6012 (12A) or RD6018 (18A), more flexible, faster charging, pretty colours, bluetooth/USB connectivity, firmware updates which appear to actually happen, does not include a PSU (they sell one that is suitable but only 800W vs max capability of 1080W), more expensive. Great intro benchtop power supply, can upgrade with a beefier PSU to handle 48v @ 18A as well.
  3. Riden/RD's DP series, like this one, which have similar features to the RD series and does not include a PSU, but does have a 20A output version. I think I would rather have the RD series with better interface, and live with 2A less current.
  4. This interesting 3-15v 50A unit and its brethren, which appear to consist of a buck converter bolted onto a range of PSUs, with a potentiometer for current and trim pot for voltage. I think it will shut off when current drops to nil - seems like a great way to do top balancing on parallel cells and then also quickly charge a larger battery bank. The 3-15v version also includes a reverse polarity protection thingy to help prevent the loss of magic smoke via a bumbling idiot's hands.
  5. Buy a super cheap buck converter with minimal controls and a cheap Ebay server PSU, rated appropriately. Could build it into a case for something that is easy to move and use. Feels janky though?
  6. Any number of much more expensive but less electrically scary than these cheaper ones.

So, #4 appears to be a pretty good option. I can top balance my cells in parallel and charge the whole bank fairly rapidly.

Or, a #1 and then a dedicated charger that has an LiFePO4 charge profile - something that floats @ 13.6v.

Thoughts? Thank you!

NO -- #4 IS A TOTAL PIECE OF SHIT RIP OFF -- TOTALLY ... BOTH @Steve_S and I fell for it ... TERRIBLE .. its a good idea but poorly put together and voltages that were all over the place (at least for mine) ... the 50A version couldn't put out 10A if it had to -- literally - the power supply is nothing more than a dell laptop charger with a variable control on it ....
 
Good to know. I actually have the 12v battery range covered with several other power supplies I have and a buck converter. Maybe I will focus on the 3 volt part of this question.
 
Last edited:
I am researching benchtop power supplies and LiFePO4 chargers. Ideally, I can purchase one device and do both top balancing as needed and charge the battery bank every now and then when I have 240v mains/shore power available.

I don't need it to function as a power supply for any DC loads except the battery cells and bank - appliances, lights etc are powered by 240v directly when available.

Currently it's a 4S 12v 272Ah LiFePO4 bank (may expand in the future) with a Daly BMS.

I have found a few options:
  1. Ones that look like this, usually 0-30v and 0-5A or 0-10A and very cheap. Seems to be the default budget option.
  2. Riden/RD's RD series, 0-60v RD6006 (6A), RD6012 (12A) or RD6018 (18A), more flexible, faster charging, pretty colours, bluetooth/USB connectivity, firmware updates which appear to actually happen, does not include a PSU (they sell one that is suitable but only 800W vs max capability of 1080W), more expensive. Great intro benchtop power supply, can upgrade with a beefier PSU to handle 48v @ 18A as well.
  3. Riden/RD's DP series, like this one, which have similar features to the RD series and does not include a PSU, but does have a 20A output version. I think I would rather have the RD series with better interface, and live with 2A less current.
  4. This interesting 3-15v 50A unit and its brethren, which appear to consist of a buck converter bolted onto a range of PSUs, with a potentiometer for current and trim pot for voltage. I think it will shut off when current drops to nil - seems like a great way to do top balancing on parallel cells and then also quickly charge a larger battery bank. The 3-15v version also includes a reverse polarity protection thingy to help prevent the loss of magic smoke via a bumbling idiot's hands.
  5. Buy a super cheap buck converter with minimal controls and a cheap Ebay server PSU, rated appropriately. Could build it into a case for something that is easy to move and use. Feels janky though?
  6. Any number of much more expensive but less electrically scary than these cheaper ones.

So, #4 appears to be a pretty good option. I can top balance my cells in parallel and charge the whole bank fairly rapidly.

Or, a #1 and then a dedicated charger that has an LiFePO4 charge profile - something that floats @ 13.6v.

Thoughts? Thank you!
I have been using #1 to charge my 24v LiFePos and one 12v LiFePo now for about six months with no issues. it holds voltage pretty steady and is giving 10a CC at the battery then drops current as it should when reaching set voltage. I did check with a VOM at the battery for accuracy. At $60 i am very satisfied with it. I do use 12g wires instead of the thin originals.
 
NO -- #4 IS A TOTAL PIECE OF SHIT RIP OFF -- TOTALLY ... BOTH @Steve_S and I fell for it ... TERRIBLE .. its a good idea but poorly put together and voltages that were all over the place (at least for mine) ... the 50A version couldn't put out 10A if it had to -- literally - the power supply is nothing more than a dell laptop charger with a variable control on it ....
Thank you and @Steve_S for your sacrifice, I will skip this unit. I am sketched out now by how insistently they say not to change the length of the cables, and how some reviews suggest they have calibrated the ammeter to the length of cabling used. I’m not sure if this is normal but yeah it means you can’t use higher gauge wires without throwing the whole thing out of whack - the current adjustment won’t go as high or low as it should be able to due to the mis-calibration and the display will be incorrect.

So, it’s between #1 and perhaps the RD6018, which appeals as it would be useful for a wider range of applications and has a reasonably priced option that includes a case and PSU, and is well-reviewed and fairly well-trusted. I also appreciate that Riden is designer, manufacturer and seller of the product. Or, judge, jury and executioner of my battery bank. HAH!
 
I have been using #1 to charge my 24v LiFePos and one 12v LiFePo now for about six months with no issues. it holds voltage pretty steady and is giving 10a CC at the battery then drops current as it should when reaching set voltage. I did check with a VOM at the battery for accuracy. At $60 i am very satisfied with it. I do use 12g wires instead of the thin originals.
Thank you for sharing your experience and another vote for this kind of unit.
 
Or this one to get me 60 Amps:

It is about $40 plus shipping.
Am I understanding correctly that you would use this to get your drained cells from 2.5v or whatever up to 3.3v (roughly 70% SOC), then use the 3.6v mean well to finish the job?
 
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