diy solar

diy solar

System check for lithium battery upgrade

Lstyles

New Member
Joined
May 31, 2021
Messages
67
I installed a lithium/solar power system in my travel trailer 2 years ago but now want to upgrade the battery to a DIY lithium so as to give myself a little more breathing room on battery capacity. I am new to DIY lithium battery builds and spent a lot of time reading the various threads on this forum but I have a couple of lingering questions I would like to get your expert opinion on. Sorry in advance for length of post but it seems its helpful to have as much information as possible for you to evaluate.

Current system:

170ah renogy lipo- 2 yrs old and works fine in present system....just want a little more capacity so I don't have to watch the battery so closely. Max d/c rate for this battery is rated at 100amps but I have been able to run the microwave for short periods of time with BMV showing 125 amps out.

Victron 2000 watt inverter multiplus 80 Amp charger-has been handling our modest AC needs but we don't need much as we don't any high power appliances such air conditioner, hair dryers etc. Microwave is the only one above 600 watts and we rarely use it.

Victron 75/15 mppt to support 220 watts of sunpower portable panels (these work great!)

Victron 100/50 mppt to support 400 watts of panels on roof

Victron Bmv 712

2/0 wire from battery to bus bar and to multiplus with 300 amp fuse between battery and system bus bar and 300 amp fuse for multiplus

Current settings for charge controllers:

absorption=14.4v
float= 13.6v

Current settings for inverter/charger:
absorption=14.2v
float=13.5v

Planned upgrade:

4 CATL 310ah cells to replace 170 ah Renogy. Daly smart BMS 4S 150a. Battery bus bars that came with the cells are 16mm x 2mm x 95mm.
I just finished top balancing the cells to 3.6v (they have drifted down to 3.54v but are all the same). As there were only 4 bus bars that came with the cells, for top balancing the cells I made six bus bars out of 5/8” copper pipe which when smashed flat are about 1” wide x 2mm thick .
I want to move on to put the battery together and put on the BMS but have a couple of lingering questions:

1. Are the supplied bus bars adequate to handle the 150 amp discharge current that the BMS can put out?
From looking at some of the ampacity tables it looks like they are right on the edge. I don't think I will ever use more than 125 amps (from 1500w microwave) and that would only be for a couple of minutes but given 150amp rating of BMS its at least possible that I could pull up to 150amps. The copper pipe bus bars I made handle a little more as they are 1" wide (as opposed to the 5/8" provided bus bars) but aren't tinned. I also have some 1/4" x 1" aluminum bar in the garage that I could use to make some bus bars but not sure what else I need to do to use aluminum.

2. What sort of compression/padding should I plan for when I put the cells into series?
I planned on compressing them with wood but then wondered if I should introduce any padding between cells (or VHB tape), around the edges of battery or underneath as these will be in a travel trailer and we sometimes take the trailer on washboard roads.

3. Once I have made the battery and attached BMS, what settings should I program into the BMS (other than battery capacity of 310ah)?

4. When the battery is assembled and BMS settings entered can I just replace the old battery with the new one?
I am assuming the 2/0 cable and 300 amp fuses will be sufficient for the potential 150a max output

5. Once the battery is attached to existing system should I change the multiplus and/or charge controller settings from what I have above?
I am not sure if change from Renogy to the CATL cells means I need different settings.

6. Any thing I am doing wrong here? I don't need to squeeze every little last amp out of the system and my emphasis is always on safety.

Thanks so much for taking the time to review this and thank you in advance for any input/help you can give me.

Lori
 
I installed a lithium/solar power system in my travel trailer 2 years ago but now want to upgrade the battery to a DIY lithium so as to give myself a little more breathing room on battery capacity. I am new to DIY lithium battery builds and spent a lot of time reading the various threads on this forum but I have a couple of lingering questions I would like to get your expert opinion on. Sorry in advance for length of post but it seems its helpful to have as much information as possible for you to evaluate.

Current system:

170ah renogy lipo- 2 yrs old and works fine in present system....just want a little more capacity so I don't have to watch the battery so closely. Max d/c rate for this battery is rated at 100amps but I have been able to run the microwave for short periods of time with BMV showing 125 amps out.

Victron 2000 watt inverter multiplus 80 Amp charger-has been handling our modest AC needs but we don't need much as we don't any high power appliances such air conditioner, hair dryers etc. Microwave is the only one above 600 watts and we rarely use it.

Victron 75/15 mppt to support 220 watts of sunpower portable panels (these work great!)

Victron 100/50 mppt to support 400 watts of panels on roof

Victron Bmv 712

2/0 wire from battery to bus bar and to multiplus with 300 amp fuse between battery and system bus bar and 300 amp fuse for multiplus

Current settings for charge controllers:

absorption=14.4v
float= 13.6v

Current settings for inverter/charger:
absorption=14.2v
float=13.5v

Planned upgrade:

4 CATL 310ah cells to replace 170 ah Renogy. Daly smart BMS 4S 150a. Battery bus bars that came with the cells are 16mm x 2mm x 95mm.
I just finished top balancing the cells to 3.6v (they have drifted down to 3.54v but are all the same). As there were only 4 bus bars that came with the cells, for top balancing the cells I made six bus bars out of 5/8” copper pipe which when smashed flat are about 1” wide x 2mm thick .
I want to move on to put the battery together and put on the BMS but have a couple of lingering questions:

1. Are the supplied bus bars adequate to handle the 150 amp discharge current that the BMS can put out?
From looking at some of the ampacity tables it looks like they are right on the edge. I don't think I will ever use more than 125 amps (from 1500w microwave) and that would only be for a couple of minutes but given 150amp rating of BMS its at least possible that I could pull up to 150amps. The copper pipe bus bars I made handle a little more as they are 1" wide (as opposed to the 5/8" provided bus bars) but aren't tinned. I also have some 1/4" x 1" aluminum bar in the garage that I could use to make some bus bars but not sure what else I need to do to use aluminum.

2. What sort of compression/padding should I plan for when I put the cells into series?
I planned on compressing them with wood but then wondered if I should introduce any padding between cells (or VHB tape), around the edges of battery or underneath as these will be in a travel trailer and we sometimes take the trailer on washboard roads.

3. Once I have made the battery and attached BMS, what settings should I program into the BMS (other than battery capacity of 310ah)?

4. When the battery is assembled and BMS settings entered can I just replace the old battery with the new one?
I am assuming the 2/0 cable and 300 amp fuses will be sufficient for the potential 150a max output

5. Once the battery is attached to existing system should I change the multiplus and/or charge controller settings from what I have above?
I am not sure if change from Renogy to the CATL cells means I need different settings.

6. Any thing I am doing wrong here? I don't need to squeeze every little last amp out of the system and my emphasis is always on safety.

Thanks so much for taking the time to review this and thank you in advance for any input/help you can give me.

Lori

0. Consider paralleling you new battery with your old. 480Ah is better than 310Ah :)

1. Generally, yes. Consider that using a wire equivalent for your bus bar also considers insulation. Uninsulated bus bars can handle lots of current. They get hot, but they dissipate quickly. I would not be concerned by 150A with your typical bus bars. If you care a lot, you can ask them to provide "double bus bars." They'll usually do it for free or very low cost.

2. Whatever you like. You find it all ways. Once clamped, they faying surfaces can't move, and any issue is unlikely. More important to cushion them externally to prevent shock.

3. Depends on the BMS, but generally, upper and lower voltage limits and low temp protection.

4. Yes to all, but see #0.

5. No. They are the same chemistry, but you should review the settings against the cell specifications.

6. Nope. Doesn't look like it.

7. See #0 :)
 
Thanks for the prompt reply!
A couple more questions for you related to what you have above:

0. I didn't think it was advised to parallel two different capacity batteries made by two different manufacturers. Am I wrong about that? Its something to consider for future if its possible but I am trying to keep weight down in my trailer so might want to see how the 310ah DIY battery works first.

1. Good to know that what they sent me should be adequate. Given your comment about insulation, should I avoid putting heat shrink on the middle of the bus bars? I was going to do that to decrease the chance of shorting things (I am a bit clumsy).

2. Would fiber tape on sides and across top/bottom be sufficient if I put on the tape while the cells were already lightly compressed? I am thinking it will be easier to add padding to outside/underneath of battery as you suggest above if I use tape as opposed to clamping cells between two pieces of wood.

3. My cells didnt come with any documents but I found some information online about CATL cells that seem to indicate that temp should be set at 5 degrees C, low voltage at 2.5v, high voltage at 3.65v. Does that make sense?

5. Not sure where to get the charge specifications for CATL cells. Perhaps I could post a thread to see what others are using?

A couple of other little details I wanted to ask about:
-Cells have posts on them but not sure what those are made of. I have heard of issues with posts stripping when torqueing the nut. How important is torqueing the nut down to recommended torque? Should I remove the posts and replace with stainless (they might actually already be stainless) and use loctite so that I can torque them down sufficiently? I don't want to create a problem that doesn't exist if its not necessary.

thanks again!
 
Thanks for the prompt reply!
A couple more questions for you related to what you have above:

0. I didn't think it was advised to parallel two different capacity batteries made by two different manufacturers. Am I wrong about that? Its something to consider for future if its possible but I am trying to keep weight down in my trailer so might want to see how the 310ah DIY battery works first.

Following the rules rigidly, yes. It's not advisable; however, it's not like one is 5-10X larger than the other, and lots of folks do it. Some folks even parallel LFP and lead-acid. IMHO, it's worth exploring. If you go that route, it's a good idea to load/charge the battery bank and use a clamp ammeter to confirm that both batteries are passing hopefully, 1) something reasonably close to their fair share of the load and definitely confirm 2) the current passing through the battery is within the battery's (and BMS) rated limits.

1. Good to know that what they sent me should be adequate. Given your comment about insulation, should I avoid putting heat shrink on the middle of the bus bars? I was going to do that to decrease the chance of shorting things (I am a bit clumsy).

It's a personal preference. You have exposed terminals anyway, and unless you're covering the entire top of the battery, there's still a shock risk. You aren't pushing the bus bars hard, so I wouldn't be concerned if you added insulation.


2. Would fiber tape on sides and across top/bottom be sufficient if I put on the tape while the cells were already lightly compressed? I am thinking it will be easier to add padding to outside/underneath of battery as you suggest above if I use tape as opposed to clamping cells between two pieces of wood.

Tape instead of clamping? That would not be my choice. The clamping helps restrain the cells, which some manufacturers indicate can significantly increase cycle life, AND it keeps the surfaces from fretting against one another. If you're going to use tape, I'd put something between the cells - very thin foam or even paperboard - like what cereal boxes are made from.

3. My cells didnt come with any documents but I found some information online about CATL cells that seem to indicate that temp should be set at 5 degrees C, low voltage at 2.5v, high voltage at 3.65v. Does that make sense?

Yep. Very common numbers for almost all of these types of cells.

5. Not sure where to get the charge specifications for CATL cells. Perhaps I could post a thread to see what others are using?

They are usually expressed as a 0.5C or 1C value. This is a multiple of the capacity in amps, i.e., 310Ah cells charged at 0.5C is 155A max. You will likely be limited more by the BMS than the cells.

A couple of other little details I wanted to ask about:
-Cells have posts on them but not sure what those are made of. I have heard of issues with posts stripping when torqueing the nut. How important is torqueing the nut down to recommended torque? Should I remove the posts and replace with stainless (they might actually already be stainless) and use loctite so that I can torque them down sufficiently? I don't want to create a problem that doesn't exist if its not necessary.

Most terminals are aluminum. 6mm Internal threads in most of these commodity cells are limited to an absolute maximum torque of 8Nm, and this value may strip the internal thread. Most recommend installing grub screws.


Personally, I use green loctite and M6-1 x 30mm grub screws with the flat bottom. 30mm is longer than I wanted, but it was what was available and cheap.

@FilterGuy has a few things to say about grub screws:

 
Thanks again for the advice. I ended up clamping them together and installing Daly smart BMS without much trouble. I am now doing a capacity test. After I have completely drained the battery during capacity test do I need to top balance cells again or can I just hook up the whole battery to my benchtop charger and set it to 14.4 volts with max current (10amp)? I know it will take a while to charge up with benchtop charger but I don’t have anything more powerful.
 
I installed a lithium/solar power system in my travel trailer 2 years ago but now want to upgrade the battery to a DIY lithium so as to give myself a little more breathing room on battery capacity. I am new to DIY lithium battery builds and spent a lot of time reading the various threads on this forum but I have a couple of lingering questions I would like to get your expert opinion on. Sorry in advance for length of post but it seems its helpful to have as much information as possible for you to evaluate.

Current system:

170ah renogy lipo- 2 yrs old and works fine in present system....just want a little more capacity so I don't have to watch the battery so closely. Max d/c rate for this battery is rated at 100amps but I have been able to run the microwave for short periods of time with BMV showing 125 amps out.

Victron 2000 watt inverter multiplus 80 Amp charger-has been handling our modest AC needs but we don't need much as we don't any high power appliances such air conditioner, hair dryers etc. Microwave is the only one above 600 watts and we rarely use it.

Victron 75/15 mppt to support 220 watts of sunpower portable panels (these work great!)

Victron 100/50 mppt to support 400 watts of panels on roof

Victron Bmv 712

2/0 wire from battery to bus bar and to multiplus with 300 amp fuse between battery and system bus bar and 300 amp fuse for multiplus

Current settings for charge controllers:

absorption=14.4v
float= 13.6v

Current settings for inverter/charger:
absorption=14.2v
float=13.5v

Planned upgrade:

4 CATL 310ah cells to replace 170 ah Renogy. Daly smart BMS 4S 150a. Battery bus bars that came with the cells are 16mm x 2mm x 95mm.
I just finished top balancing the cells to 3.6v (they have drifted down to 3.54v but are all the same). As there were only 4 bus bars that came with the cells, for top balancing the cells I made six bus bars out of 5/8” copper pipe which when smashed flat are about 1” wide x 2mm thick .
I want to move on to put the battery together and put on the BMS but have a couple of lingering questions:

1. Are the supplied bus bars adequate to handle the 150 amp discharge current that the BMS can put out?
From looking at some of the ampacity tables it looks like they are right on the edge. I don't think I will ever use more than 125 amps (from 1500w microwave) and that would only be for a couple of minutes but given 150amp rating of BMS its at least possible that I could pull up to 150amps. The copper pipe bus bars I made handle a little more as they are 1" wide (as opposed to the 5/8" provided bus bars) but aren't tinned. I also have some 1/4" x 1" aluminum bar in the garage that I could use to make some bus bars but not sure what else I need to do to use aluminum.

2. What sort of compression/padding should I plan for when I put the cells into series?
I planned on compressing them with wood but then wondered if I should introduce any padding between cells (or VHB tape), around the edges of battery or underneath as these will be in a travel trailer and we sometimes take the trailer on washboard roads.

3. Once I have made the battery and attached BMS, what settings should I program into the BMS (other than battery capacity of 310ah)?

4. When the battery is assembled and BMS settings entered can I just replace the old battery with the new one?
I am assuming the 2/0 cable and 300 amp fuses will be sufficient for the potential 150a max output

5. Once the battery is attached to existing system should I change the multiplus and/or charge controller settings from what I have above?
I am not sure if change from Renogy to the CATL cells means I need different settings.

6. Any thing I am doing wrong here? I don't need to squeeze every little last amp out of the system and my emphasis is always on safety.

Thanks so much for taking the time to review this and thank you in advance for any input/help you can give me.

Lori
One suggestion, upgrade to the Daly 250 amp BMS. It comes with 2 gauge wire, and the price difference is not great.

Remember that busbars are generally not supplied by the battery manufacturer, but are usually procured and added by the vendor you purchased the cells from. Without any details, really nobody has a clue if the ones you have are sufficient.
Double check all BMS settings, Daly frequently does stupid things. My 12v Daly BMS was factory set for Li-ion rather than LiFePO4, so it still has zero cycles on it (since I refuse to charge to 3.7v per cell). A few other settings (like charge enabled to -20 C) were off.

If you really think 150 amps is enough, you might want to consider the cheaper and generally better JBD BMS. Their 150 amp model seems rock solid and accurately rated. You will have to make your own battery cables for it. I've not completely tested mine yet, but so far I'm impressed. Making two cables out of 6 gauge silicon wire isn't that hard for the JBD.

 
Thanks again for the advice. I ended up clamping them together and installing Daly smart BMS without much trouble. I am now doing a capacity test. After I have completely drained the battery during capacity test do I need to top balance cells again or can I just hook up the whole battery to my benchtop charger and set it to 14.4 volts with max current (10amp)? I know it will take a while to charge up with benchtop charger but I don’t have anything more powerful.
If you've already top balanced the cells, leave them in the pack and charge. Charging as a pack is 4 times as fast as charging in parallel.

10 amps is slow, but it will certainly get the job done.
 
Thanks for the advice on the BMS. I already have the Daly 150 amp and since my inverter is only 2000 watts I think I will be fine. We really don’t have many high power appliances and have done fine with the existing renogy which has 100 amp discharge max (although as I said above it did put out 125 amps at one point. Thanks also for the info on charging the pack after the capacity test. I wasn’t sure how to approach that once the battery has been discharged and BMS stops everything. I guess I might have to “jump” the BMS again but will charge batteries first and see what happens. So far Daly BMS has worked fine although SOC seems to be a moving target. I have a Victron BMV so not really worried about that though.
 
Thanks for the advice on the BMS. I already have the Daly 150 amp and since my inverter is only 2000 watts I think I will be fine. We really don’t have many high power appliances and have done fine with the existing renogy which has 100 amp discharge max (although as I said above it did put out 125 amps at one point. Thanks also for the info on charging the pack after the capacity test. I wasn’t sure how to approach that once the battery has been discharged and BMS stops everything. I guess I might have to “jump” the BMS again but will charge batteries first and see what happens. So far Daly BMS has worked fine although SOC seems to be a moving target. I have a Victron BMV so not really worried about that though.
Newer Daly BMS Bluetooth dongles now have a wake up switch as a black dot just to the right of the word "Bluetooth", if you were lucky and got one, no need to jump the BMS. Just charging the pack should wake it up as well.

When you parallel the batteries, make sure the voltages are pretty close, like a tenth of a volt close. If they are far enough apart, you could get some significant current flow between them.
 
Wow! I did not notice that little dot. I have it on my dongle. So does pushing the dot allow me to wake up the BMS like shorting out the two pins? I am charging pack back up now so will see if I need to use the dot.
 
Wow! I did not notice that little dot. I have it on my dongle. So does pushing the dot allow me to wake up the BMS like shorting out the two pins? I am charging pack back up now so will see if I need to use the dot.
That is what Daly says. I don't have one of the new ones, so can't really verify it. Just saw it on their Aliexpress store a day or two ago.
A welcome addition, motivated I'm sure by a lot of people returning their BMS that is working fine. Serves them right.
 
Just to report back in functionality of “dot” on BT dongle. It did not work to wake up the BMS. Charging the battery did wake it up. So the little “dot” did not seem to work for me.
I have another question about securing battery now that it is together. It is clamped together with two boards on ends. I planned on securing it to the floor of travel trailer but I am thinking some padding between battery and floor would be a good idea to soften impact of road bumps.
Any suggestions on how to cushion the battery?
 
Just to report back in functionality of “dot” on BT dongle. It did not work to wake up the BMS. Charging the battery did wake it up. So the little “dot” did not seem to work for me.
I have another question about securing battery now that it is together. It is clamped together with two boards on ends. I planned on securing it to the floor of travel trailer but I am thinking some padding between battery and floor would be a good idea to soften impact of road bumps.
Any suggestions on how to cushion the battery?
Thanks for letting us know. It might only work on a "new" design. Like I said, I just noticed it a couple of days ago in their store.
 
Still looking for advice on how to pad or decrease impact of movement/jolts on the battery when it is in the trailer??
Also, my cells came with threaded “posts” already seated in the aluminum female terminals at positive/negative ends of the cell. The terminal is aluminum but the posts are not as they are magnetic. I have just been tightening the nut on the posts lightly so far and haven’t noticed the post twisting in the female terminal. Unlike a hex ended grub screw there is no hex or other other way to control the spin on the existing posts. Should I replace the posts with SS grub screws with a hex end to prevent the post from turning in the female terminal? I hear the female terminals are soft and tend to strip with even a couple of “uses” (screwed in and out) so removing the existing posts and replacing with SS gru screws could theoretically do more harm. Should I just leave it alone or make the change? Would double nutting the existing posts help?
 
I want to reopen my original post because i am now considering paralleling the two batteries I mentioned above. The suggestion from Snoobler was to parallel my batteries. I didn’t need the capacity of both batteries at the time and wanted to save on weight in trailer. Things have been working fine but seeing that 170ah renovation battery sitting there unused is bothering me! ?
To recap, I had a 170ah renovation that I replaced with a 305 ah DIY battery. System has been working fine but now I think I want to add the 170ah renovation to make a larger battery bank. From some reading it appears I can just hook up the 170ah battery to the positive bus bar of the system so that the batteries are in parallel. It looks like the key things are to make sure the battery cables to the positive bus bar are the same length as the cables from 305ah battery. Also I should have a separate fuse for the new battery. Anything I am missing here??
Thanks in advance for all your help!
 
I want to reopen my original post because i am now considering paralleling the two batteries I mentioned above. The suggestion from Snoobler was to parallel my batteries. I didn’t need the capacity of both batteries at the time and wanted to save on weight in trailer. Things have been working fine but seeing that 170ah renovation battery sitting there unused is bothering me! ?
To recap, I had a 170ah renovation that I replaced with a 305 ah DIY battery. System has been working fine but now I think I want to add the 170ah renovation to make a larger battery bank. From some reading it appears I can just hook up the 170ah battery to the positive bus bar of the system so that the batteries are in parallel. It looks like the key things are to make sure the battery cables to the positive bus bar are the same length as the cables from 305ah battery. Also I should have a separate fuse for the new battery. Anything I am missing here??
Thanks in advance for all your help!
You first said it was a lipo battery, but the charge values you gave are more LFP. If it is an LFP (very likely), then just get the voltage pretty close and parallel away.
 
Sorry both are LFP not Lipo. I will be sure to charge up both batteries before connecting everything.
Thanks!
 
Back
Top