Joined
·
2,059 Posts
I've had several private emails about my DIY grid charger/discharger and decided to start a thread here so everyone can get the same info. I'm also curious how many people have built one of them from my article/schematic.
Here's the first question/answer to a recent post on the forum:
----
[edits]
Please read these corrections for the V2 charger:
10/17/2020] Basically all the problems that were mentioned in this #1 post have been eliminated in V2 of my DIY grid charger/discharger. The V2 power supply uses a single constant current supply that can output 200 volts maximum at 350 ma. I'd rather see 176 volts but you gott'a use what's available.
10/20/2020 I've added a way to start a V2 grid charge on a battery that has completely discharged from sitting a long time. It's all explained at the bottom of the V2 article on my website.
[/edits]
----
The rest of this post is the original #1 post for historical whatever.
You MUST use current limited power supplies. Not constant current supplies for a grid charger. The difference is subtle but most constant current supplies wired in series will not track properly. Unfortunately eBay Chinese sellers of LED power supplies have almost all switched over to constant current supplies and the current limited supplies are very hard to find. If I find a current seller of a 45-90 volt supply I will post it here.
I have tested several different constant current pairs and typically the first supply that reaches it's maximum current (considering the load) will prevent the other supply from delivering 1/2 of the voltage to charge the battery due to a race problem when the supplies start up. This will cause one supply to operate above it's wattage rating. I will describe this further near the end of this section.
The following are the results of two typical Chinese 60-90 volt, constant current 300 ma supplies that I recently tested.
Test 1: Test both supplies individually for consistency.
Supply #1: (Tested by itself)
No load voltage: 126 volts
Loaded with two 40 watt light bulbs in series: 89.9 volts @280 ma (after 10 minute warm up)
Supply #2: (Tested by itself)
No load voltage: 131 volts
Loaded with two 40 watt light bulbs in series: 88.5 volts @275 ma (after 10 minute warm up)
Test 2: With both supply's outputs wired in series
No load voltage: 261 volts (NOT 180 volts as you would expect from two 60-90 volt supplies in series.)
This is actually normal for a constant current supplies. The no load output voltage has to be higher than the expected loaded voltage to deliver the maximum specified constant current to the load.
A limited current supply has a maximum voltage it can deliver (for instance 60-90 volts) and will if necessary, also limit the current so as to not exceed it's rated maximum output current. That is the subtle difference between the two types of supplies. The lower rating (60 in this case) is the lower limit for normal operation.
Test #3: Check individual load voltage of the two series connected supplies.
Load with two 40 watt light bulbs connected in series to simulate charging current: 120 volts @ 239 (that sounds reasonable)
Output voltage of each series connected supply: (Wait till you see the next test readings @ 239 ma!!)
Supply #1: 4 volts (Yes, FOUR volts!)
Supply #2: 116 volts
Obviously these two typical non-precision constant current supplies are just not going to work for our grid charger since each supply is rated as a 25 watt supply. One supply is overloaded and doing most of the work and the other one basically took the day off.
Here's what caused one supply to only output 4 volts. When the AC power switch is set to ON there is a voltage/current race problem between the two supplies wired in series until one of them reaches it's constant current condition.
Since the supplies are wired in series, power supply #2 with the lower constant current capability with that load will have also reached it's maximum capable voltage at that maximum current. Supply #1 then fills in the remaining voltage (only 4 volts in this test) because of the current supply #2 is already forcing through both supplies. The higher current capable supply #1 can't force more current through the series connected supplies to balance the voltages because supply #2 won't allow any more current to flow.
Current limited supplies don't have the race problem because they each put out the their maximum voltage listed (90 volts) and if necessary limit the current to their maximum specified current. Yes the lower max current supply rules but only after it reaches it's specified voltage. Since the lower current sets the current the other supply is able to also output 90 volts for a total of 180V.
----
Here's some tips of what I did when building and using the grid charger that I didn't include in my website article.
1. I'd like to emphasize that if possible use a top mounted 120mm fan to make it much easier to mount the multi meter on the main part of the ATX case. And it gives you a little more leeway on mounting the LED driver supplies since the fan is not in the way.
2. Another thing that might help some builders: I used a normal 12v/5v Molex female power connector on the charger end of the charging harness. For the mating male connector on the grid charger I hack sawed off the male connector and a little of the metal work around it from a junk hard drive. I was then able to mount the male connector on the front of my grid charger and just plug the end of the charging harness into that connector.
3. I also use a normal flexible Molex power connector cover on the charging harness female connector when not charging the car. I find those black flexible covers on junk DELL desktop computers.
4. I haven't found any of the 3 digit multi-meters that show the voltage and current at the same time that display 1/10s of a volt above 100 volts. i.e. 165.3 will appear as 165 volts. I find it very useful to be able to see the tenths of a volt. Especially so near the end of the charge when you want to see the trend of voltage change when the change may only be 0.2 volt per hour!
5. I just checked and there are quite a few LED drivers that look the same as the ones I used but they have output voltage ranges that are either much too high or too low. So builders will have to be careful and only order the drivers that output 45 to 90 volts DC. I only found one vendor at the present time that has the voltage range needed and have updated the BOM to that eBay listing.
----
I would appreciate if you have ordered the parts, are building or have finished building one of these grid chargers that you go to my Google spreadsheet to give me an idea where you're at in the build. The grid charger/discharger has been the most read of everything on my website so I am just interested in how many people have built a charger from it.
Thank you.
Link to google spreadsheet.
Here's the first question/answer to a recent post on the forum:
No changes after adding the discharge connector and wires.Coincidentally it's your charger that I'm planning on making once the parts finish slow-boating their way from the various ends of the earth.
I thought it might be mine when you said it had a discharge connector.
Any changes or updates to what you have on your site?
----
[edits]
Please read these corrections for the V2 charger:
10/17/2020] Basically all the problems that were mentioned in this #1 post have been eliminated in V2 of my DIY grid charger/discharger. The V2 power supply uses a single constant current supply that can output 200 volts maximum at 350 ma. I'd rather see 176 volts but you gott'a use what's available.
10/20/2020 I've added a way to start a V2 grid charge on a battery that has completely discharged from sitting a long time. It's all explained at the bottom of the V2 article on my website.
[/edits]
----
The rest of this post is the original #1 post for historical whatever.
You MUST use current limited power supplies. Not constant current supplies for a grid charger. The difference is subtle but most constant current supplies wired in series will not track properly. Unfortunately eBay Chinese sellers of LED power supplies have almost all switched over to constant current supplies and the current limited supplies are very hard to find. If I find a current seller of a 45-90 volt supply I will post it here.
I have tested several different constant current pairs and typically the first supply that reaches it's maximum current (considering the load) will prevent the other supply from delivering 1/2 of the voltage to charge the battery due to a race problem when the supplies start up. This will cause one supply to operate above it's wattage rating. I will describe this further near the end of this section.
The following are the results of two typical Chinese 60-90 volt, constant current 300 ma supplies that I recently tested.
Test 1: Test both supplies individually for consistency.
Supply #1: (Tested by itself)
No load voltage: 126 volts
Loaded with two 40 watt light bulbs in series: 89.9 volts @280 ma (after 10 minute warm up)
Supply #2: (Tested by itself)
No load voltage: 131 volts
Loaded with two 40 watt light bulbs in series: 88.5 volts @275 ma (after 10 minute warm up)
Test 2: With both supply's outputs wired in series
No load voltage: 261 volts (NOT 180 volts as you would expect from two 60-90 volt supplies in series.)
This is actually normal for a constant current supplies. The no load output voltage has to be higher than the expected loaded voltage to deliver the maximum specified constant current to the load.
A limited current supply has a maximum voltage it can deliver (for instance 60-90 volts) and will if necessary, also limit the current so as to not exceed it's rated maximum output current. That is the subtle difference between the two types of supplies. The lower rating (60 in this case) is the lower limit for normal operation.
Test #3: Check individual load voltage of the two series connected supplies.
Load with two 40 watt light bulbs connected in series to simulate charging current: 120 volts @ 239 (that sounds reasonable)
Output voltage of each series connected supply: (Wait till you see the next test readings @ 239 ma!!)
Supply #1: 4 volts (Yes, FOUR volts!)
Supply #2: 116 volts
Obviously these two typical non-precision constant current supplies are just not going to work for our grid charger since each supply is rated as a 25 watt supply. One supply is overloaded and doing most of the work and the other one basically took the day off.
Here's what caused one supply to only output 4 volts. When the AC power switch is set to ON there is a voltage/current race problem between the two supplies wired in series until one of them reaches it's constant current condition.
Since the supplies are wired in series, power supply #2 with the lower constant current capability with that load will have also reached it's maximum capable voltage at that maximum current. Supply #1 then fills in the remaining voltage (only 4 volts in this test) because of the current supply #2 is already forcing through both supplies. The higher current capable supply #1 can't force more current through the series connected supplies to balance the voltages because supply #2 won't allow any more current to flow.
Current limited supplies don't have the race problem because they each put out the their maximum voltage listed (90 volts) and if necessary limit the current to their maximum specified current. Yes the lower max current supply rules but only after it reaches it's specified voltage. Since the lower current sets the current the other supply is able to also output 90 volts for a total of 180V.
----
Here's some tips of what I did when building and using the grid charger that I didn't include in my website article.
1. I'd like to emphasize that if possible use a top mounted 120mm fan to make it much easier to mount the multi meter on the main part of the ATX case. And it gives you a little more leeway on mounting the LED driver supplies since the fan is not in the way.
2. Another thing that might help some builders: I used a normal 12v/5v Molex female power connector on the charger end of the charging harness. For the mating male connector on the grid charger I hack sawed off the male connector and a little of the metal work around it from a junk hard drive. I was then able to mount the male connector on the front of my grid charger and just plug the end of the charging harness into that connector.
3. I also use a normal flexible Molex power connector cover on the charging harness female connector when not charging the car. I find those black flexible covers on junk DELL desktop computers.
4. I haven't found any of the 3 digit multi-meters that show the voltage and current at the same time that display 1/10s of a volt above 100 volts. i.e. 165.3 will appear as 165 volts. I find it very useful to be able to see the tenths of a volt. Especially so near the end of the charge when you want to see the trend of voltage change when the change may only be 0.2 volt per hour!
5. I just checked and there are quite a few LED drivers that look the same as the ones I used but they have output voltage ranges that are either much too high or too low. So builders will have to be careful and only order the drivers that output 45 to 90 volts DC. I only found one vendor at the present time that has the voltage range needed and have updated the BOM to that eBay listing.
----
I would appreciate if you have ordered the parts, are building or have finished building one of these grid chargers that you go to my Google spreadsheet to give me an idea where you're at in the build. The grid charger/discharger has been the most read of everything on my website so I am just interested in how many people have built a charger from it.
Thank you.
Link to google spreadsheet.