Too Parallel - when is it too much - Max Parallel connections?
- Thread starter OfflineAlberta
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robbob2112
Doing more research, mosty harmless
Thanks Jim,
And, there is only ONE way to bake proper cornbread.
And, there is only ONE way to bake proper cornbread.
robbob2112
Doing more research, mosty harmless
I need a set of those
robbob2112
Doing more research, mosty harmless
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I intend using a YR1035 meter to measure impedance from the inverter end of the cable through a single set of batteries.. then switch batteries and repeat... match them by shortening a battery cable...
I've recently posted more results for longer parallel strings: https://diysolarforum.com/threads/calculation-of-parallel-string-currents-addendum.94178/When you say string, that typically refers to serial connections. You have 6 12V in parallel and want to add 4 more in parallel.
Honestly, I'm shocked to hear some manufacturer recommended 8. The most is typically 2-4.
The fundamental issue is that the more batteries you have in parallel, the harder it is to get them to share current equally.
Please see line #6 in my signature. Victron discusses it in detail.
This post:
Also discusses it.
Haaaa… on that topic, 40 years + ago I used to cook a lot chilie in the eighty’s on a snowy winter day…….there are several good prepared mix of spices you can buy and add the other fresh stuff to suit your need…
I often used the Carrol Shelby’s brown bag of spice mix…
One time I was sitting there watching it simmer and having a drink and looked down at the side of the bag and found this pic and ole saying on the bag…
I thought , ya know.. there’s alot of truth in those words… love em or hate em…lota of truth….everyone loved it ……and no one got offended…
…and I tore it out and saved it..
That’s been 40- 45 years ago ..it still stays in my kitchen as a fond link to a better time in life..
They still sell ole Shelbys chilie spices but they have changed the packaging. And removed the old pic and sayin…
J.
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robbob2112
Doing more research, mosty harmless
My favorite off the shelf mix is Morrison's cornkits. Made in a cast iron skillet with bacon grease ... it is NOT loaded with sugar like nearly all of the box mixes...
OfflineAlberta
New Member
Thank you for all your work, your theory work is really useful to the community. I did read over your work on larger parallel strings. It is definitely what I am seeing with my array.
Though I noticed that all the constructs are linear in design. Do you think that balance issue could be addressed maybe by design as well? Perhaps you could put your math to work in my theoretical construct (I don't have the math skills). Though I have not drawn the design out but I can give a written description and since you have a decently working mind's eye (like most people in this space) I hope you can see what I am seeing.
My concept is to arrange all batteries in a decagon formation with all terminals facing inward (My batteries have terminals on the corners at the widest part of a rectangle, I also have 10 batteries that I would like to use). Using a busbar to connect the terminal together (Direct with no wires) and having the busbar ends soldered together to create a contiguous circle. This would be done for both positive and negative. Then in the increments of every two batteries there is a copper bar soldered facing toward the center of the ring (equally placed naturally). This would be done a total of 5 times for a 10 battery config. This configuration would not work as well with odd numbered batteries. In the center where the 5 leads meet a disk of copper is soldered symmetrically to the leads. At the center point is where wire leads for the inverter (Load) would connect. To my understanding this should give a high probability of access to all the batteries equally, forgiving material deficiencies if any.
The way I see it, the issue of balance for the batteries (both charging and discharging) is a matter of accessibility. In a linear configuration it is impossible to achieve equal accessibility but in a star configuration it is inherent in the design. I think linear layouts really only apply to lead acid style batteries since they can't be mounted but in one orientation. We keep on treating the LFP batteries as if they are Lead batteries.
Any and all feedback is welcome.
Consider the "posts" configuration:
The batteries don't have to be arranged in a straight line as shown in the image. Is your proposed configuration a version of posts but with the batteries in a circle? The copper disc in the center could be like this: https://diysolarforum.com/threads/c...ing-battery-currents.37937/page-5#post-754439
For a circular "posts" type configuration probably no math is needed.
The batteries don't have to be arranged in a straight line as shown in the image. Is your proposed configuration a version of posts but with the batteries in a circle? The copper disc in the center could be like this: https://diysolarforum.com/threads/c...ing-battery-currents.37937/page-5#post-754439
For a circular "posts" type configuration probably no math is needed.
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OfflineAlberta
New Member
Yes the pentagon would be a good shape for the center connection peace in my proposed design. Thank you for the suggestion!Consider the "posts" configuration:
View attachment 256838
The batteries don't have to be arranged in a straight line as shown in the image. Is your proposed configuration a version of posts but with the batteries in a circle? The copper disc in the center could be like this: https://diysolarforum.com/threads/c...ing-battery-currents.37937/page-5#post-754439
For a circular "posts" type configuration probably no math is needed.
I do have a question of ignorance on my part, this is regarding fuses and or breakers in front of each battery. What exactly are we protecting against? I can logically deduce it is an overload condition of some sort, however I am unable to "See" the circumstances that those overload conditions would occur. Right now I don't have anything in front of each individual batteries, I don't want to die stupid and so if I can get the Coles notes on the situations that could bring the overload condition I would love that!
Second question I have, some use T class fuses and some use breakers and then some use fuses and breakers (as described from the post you referenced above)? And yet still I see someone use fuses, breakers and a switch. Part of me thinks that some of these configs are "overkill" paranoia stuff .... you know the idea that you can never be too safe... the way I see it, a good quality breaker (midnight solar) should be sufficient for overload protection and to function as a switch.
I know some of these questions are pretty newbie and maybe they are answered somewhere else. Forgive my ignorance in this ... but I do learn pretty quickly.
Thanks again to all that contribute to this space, it is of really great service.
ricardocello
Watching and Learning
If one of your 10 batteries develops an internal short, the other 9 have a direct path to send all of their current through to that short. Result: Big big fire. Nine on one isn’t a fair fight.
Same if you accidentally short one of the cables. All of the batteries will send their current. Fuses/breakers protect the wiring and batteries and hopefully avoid the armageddon of your house burning down.
robbob2112
Doing more research, mosty harmless
When paralleling batteries a fault in a cell in a single one can present at the battery post as a lower voltage. This means that the other parallel batteries will dump current into the faulted battery.
Assume 4 x 100ah batteries and 1 has a fault. 3 batteries dump 100amps into the damaged one so you have 300amps coming in. The BMS might stop this depending on the original fault or it might cause catastrophic failure.
All of the LFP vendors state 4p as the max parallel. The reason is the bms is unable to block the current from more than that in parallel in case of a fault.
They also state 4s as max, because the bms can't stand up to the voltage of more than that in series.
The fuse on each battery is to protect a faulted one from the current dump of the neighbors.
For 12v batteries the MRBF fuse has an AIC of 10ka. At 48v it is 2ka. The class T is 20ka. If you use a breaker in place of a fuse you need to check that it has as high an AIC as the fuse would.
For 12v MRBF
For over that class T or breaker with 20ka AIC, the midnite breakers trip from magnetic instead of heat so they are quicker acting and more sensitive to over current. The also have a high AIC in the right series
Assume 4 x 100ah batteries and 1 has a fault. 3 batteries dump 100amps into the damaged one so you have 300amps coming in. The BMS might stop this depending on the original fault or it might cause catastrophic failure.
All of the LFP vendors state 4p as the max parallel. The reason is the bms is unable to block the current from more than that in parallel in case of a fault.
They also state 4s as max, because the bms can't stand up to the voltage of more than that in series.
The fuse on each battery is to protect a faulted one from the current dump of the neighbors.
For 12v batteries the MRBF fuse has an AIC of 10ka. At 48v it is 2ka. The class T is 20ka. If you use a breaker in place of a fuse you need to check that it has as high an AIC as the fuse would.
For 12v MRBF
For over that class T or breaker with 20ka AIC, the midnite breakers trip from magnetic instead of heat so they are quicker acting and more sensitive to over current. The also have a high AIC in the right series
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OfflineAlberta
New Member
Thank you for your response! You have given me some more insight into important considerations. I hope you can indulge some more of my ignorance. Specifically which "Series" in the midnight lineup would have the best protection. I personally like the idea of a breaker as it functions both as switch and protective element and they are reusable.
As for the max parallel of four, my batteries specifically say that 8 Parallel. Does this mean that they have a higher internal protection method to allow for current dumps should they happen? Another question that I have is about the breaker terminals, they often have relatively small terminals which really restrict cable thickness, what is the best way to overcome that.
Thank you again for your time in helping me to lens this.
OfflineAlberta
New Member
Thank you for your response! You have given me some more insight into important considerations. I hope you can indulge some more of my ignorance. Specifically which "Series" in the midnight lineup would have the best protection. I personally like the idea of a breaker as it functions both as switch and protective element and they are reusable.
As for the max parallel of four, my batteries specifically say that 8 Parallel. Does this mean that they have a higher internal protection method to allow for current dumps should they happen? Another question that I have is about the breaker terminals, they often have relatively small terminals which really restrict cable thickness, what is the best way to overcome that.
Thank you again for your time in helping me to lens this.
OfflineAlberta
New Member
Thank you for your response! You have given me some more insight into important considerations. I hope you can indulge some more of my ignorance. Specifically which "Series" in the midnight lineup would have the best protection. I personally like the idea of a breaker as it functions both as switch and protective element and they are reusable.
As for the max parallel of four, my batteries specifically say that 8 Parallel. Does this mean that they have a higher internal protection method to allow for current dumps should they happen? Another question that I have is about the breaker terminals, they often have relatively small terminals which really restrict cable thickness, what is the best way to overcome that.
Thank you again for your time in helping me to lens this.
OfflineAlberta
New Member
Thank you for your response! You have given me some more insight into important considerations. I hope you can indulge some more of my ignorance. Specifically which "Series" in the midnight lineup would have the best protection. I personally like the idea of a breaker as it functions both as switch and protective element and they are reusable.
As for the max parallel of four, my batteries specifically say that 8 Parallel. Does this mean that they have a higher internal protection method to allow for current dumps should they happen? Another question that I have is about the breaker terminals, they often have relatively small terminals which really restrict cable thickness, what is the best way to overcome that.
Thank you again for your time in helping me to lens this.
OfflineAlberta
New Member
Just to clarify, would a breaker like this work as overload protection for a battery.
Mini breaker with EM assist
I know this is not a Midnight Solar But for the price difference is it worth trying? The Midnight solar breaker that handles at least 100A is nearly 100$ for 1
HarryN
Solar Addict
robbob2112
Doing more research, mosty harmless
Depends on the size and voltage of the batteries - for 12v MRBF fuse on the post - for 24v the same - I like each battery to have a cutoff switch so that can either be a battery disconnect switch or a midnite solar breaker with a high AIC.
I am debating if I want to use a 2 pole breaker to cut off each battery totally or just a single pole on the positive side --- more reading and thinking to do on that.
Note - with 8 in parallel I would figure the current draw you expect from each and use the smaller class T fuses - this shape
Read this
and your MFG saying you can do 8 parallel probably does mean they tested it to a higher standard to prevent current when the mosfets are off.
I am debating if I want to use a 2 pole breaker to cut off each battery totally or just a single pole on the positive side --- more reading and thinking to do on that.
Note - with 8 in parallel I would figure the current draw you expect from each and use the smaller class T fuses - this shape
Read this
and your MFG saying you can do 8 parallel probably does mean they tested it to a higher standard to prevent current when the mosfets are off.
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