Solarfun4jim
Solar seduced :-)
So, instead of drawing off 0.8A from one relay output, it would only draw 0.4A from each, thus reducing the overall wattage 'wastage'???
parallel bms?
- Thread starter Ken Jones
- Start date
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yes. If both are on, they would share the load, however, since the small current relays are only on for short time, the power draw is not really a concern. The advantage of sharing the relay and charge resistor is primarily cost and simplicity.
Solarfun4jim
Solar seduced :-)
I have already thought about simplifying everything...if i go down that route, then i will simply go for 16S 400ah cells....job done, one bms, less relays, balancers etc etc(still pondering such)...no redundancy or emergency power in that scenario though. If you lose your power on route 500, your going to have a miserable week....lol.
Solarfun4jim
Solar seduced :-)
Filterguy...
Could one of these be modified to work??/
www.aliexpress.com
Could one of these be modified to work??/
15.98US $ |4 Channel NPN Type 48V 10A Power Relay Interface Module,SONGLE SRD 48VDC SL C Relay.|Relays| - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
YUP. This gets into a lot of "what if" speculation and guessing. One thing to keep in mind: There is a pretty good correlation between simplicity and reliability. If you double everything up, there are 2 times the number of components that can fail.
There is no clear answer to which is better.... but I'll toss out a few counter opinions to ponder.
Active vs Passive. Yes active can balance things quicker and across the full voltage range, but how important is that? I don't recommend it but some people run their systems with no balancing at all! Assuming you have reasonably healthy cells, the only advantage of balancing is that you can charge your bank a little bit more at the top and discharge your bank a little bit more at the bottom. With active balancing, you get to squeeze both the top and bottom. With passive balancing you can squeeze a little bit more at the top. Passive balancing is slower, but most systems spend most of their life fully charged so there is plenty of time for passive balancing to do its thing. So.... given all that, how important is active balancing to you? Do you need that extra little bit?
How important is it to monitor each cell? If you are starting with good matched cells, there is a good chance that they will all degrade at about the same rate. Furthermore, it the 2P16S configuration, you can still narrow it down to a pair of cells. Is the added complexity worth the ability to narrow it down further?
I understand that priorities and requirements will drive the solution. But I also Know that almost every requirement will incur a cost somewhere . Consequently, engineering becomes the art of trade-offs. I see beauty in simplicity so I tend to lean toward the simpler designs....but everyone has different requirements, values and opinions, so we all make different choices. (Thank god that is true, if we were all identical the world would be a pretty boring place)
Solarfun4jim
Solar seduced :-)
My worry, with large cells, is 'one cell' drift, over time. I'm looking to do this right first time and never look at it again. If active balancing keeps the cells balanced all the time, i'm happy. Regarding keeping lifepo4 cells fully charged all the time, that is not my intention. I would prefer(after top balancing) to run my cells to around 80-90% soc and certainly as soon as the charge cycle reaches what i need as 'full' i would be looking to drop the 'float' voltage down below 3.4v/cell thus stopping any further current. Only looking to discharge to 3.25v/cell, so certainly not taxing the bank. I'm looking for longevity and maintainance free.
If i can spend a little more money(but not crazy more) to ensure i am not scratching my head in a couple of years time, wondering how everything works, then thats my aim. Build it once, make it last.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
No, but this one might work.Filterguy...
Could one of these be modified to work??/
15.98US $ |4 Channel NPN Type 48V 10A Power Relay Interface Module,SONGLE SRD 48VDC SL C Relay.|Relays| - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
15.98US $ |4 Channel PNP Type 48V 10A Power Relay Interface Module,SONGLE SRD 48VDC SL C Relay.|Relays| - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
Do you have the BMS and delay board on hand? If so could you put an ohm meter between the negative posts of the various relay outputs on the delay board? Is it zero ohms? If so, the grounds are all tied together and the PNP board should work fine.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Hold on.... I need to check something..... this board may not work. I'll be back to you in a few minutes.No, but this one might work.
15.98US $ |4 Channel PNP Type 48V 10A Power Relay Interface Module,SONGLE SRD 48VDC SL C Relay.|Relays| - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
Do you have the BMS and delay board on hand? If so could you put an ohm meter between the negative posts of the various relay outputs on the delay board? Is it zero ohms? If so, the grounds are all tied together and the PNP board should work fine.
Solarfun4jim
Solar seduced :-)
I dont i'm afraid....this is all research for me, before i spend my dosh on too many stupid mistakes....lol.No, but this one might work.
15.98US $ |4 Channel PNP Type 48V 10A Power Relay Interface Module,SONGLE SRD 48VDC SL C Relay.|Relays| - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
Do you have the BMS and delay board on hand? If so could you put an ohm meter between the negative posts of the various relay outputs on the delay board? Is it zero ohms? If so, the grounds are all tied together and the PNP board should work fine.
Solarfun4jim
Solar seduced :-)
I thought the switching voltage might be too low?
Solarfun4jim
Solar seduced :-)
@FilterGuy
Mate, i will need to catch up tomorrow...it is after 3am here and my eyes are shutting...lol.
Thanks a ton for all your help, been really enjoyable. Cheers
Mate, i will need to catch up tomorrow...it is after 3am here and my eyes are shutting...lol.
Thanks a ton for all your help, been really enjoyable. Cheers
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I hear you!!!!
I wondered about that. Have a good sleep!
OK.... I am clearly getting tired too.
* The 48 volt one won't work because the output from the chargery is 12 V.
* The 12 Volt one I pointed to won't work because it needs a 12volt power in (Constant on)
Going a different rout, This would work:
https://www.amazon.co.uk/MICTUNING-Fuse-Relay-Switch-Harness/dp/B07CF7T5SY/
Since they are indipendent relays, the coils are completely seperate and it does not matter how the delay board driver works. They have an added bonus of having the coil circuit fused.
Solarfun4jim
Solar seduced :-)
Thanks for that filterguy.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
@Solarfun4jim. I think the wiring you show may not be correct. I do not have direct experience with chargery but I have read the manual (a few times). The instructions on the relay delay controller are not very clear, but he key for me was this line in the instructions:
" When large current relay closed, the small relay will be open automatically according to the below connection diagram."
I *think* this is the way it would be wired if you have an All-In-One:
View attachment 5356
Notice that the small discharge relay is not in series with the large discharge relay, instead it creates a bypass to the large discharge relay.
Note: My diagram is for a single BMS. You would put two sets of these in series for two BMSs. However, you could also rearrange the circuit to use a single discharge resistor like this:
View attachment 5358
With a couple of diodes, this can be further simplified:
View attachment 5360
Note: The flyback diode that is mentioned below would work for these diodes.
With this, the signals for the small discharge relays are "OR'd" (If either one OR the other of the signals are on, the relay turns on). (The diodes are probably not be necessary, but I would need to see the circuit of the delay board to say for sure.)
I am still pondering the best way to combine the Large Discharg relays and the Charge relays. Conceptually, 'all' you have to do is "AND" all four signals to drive one relay. If I come up with a circuit I like, I'll post it here.
One more thing: All the relays should have a flyback diode across the coil Here are some comments from Will's latest video that describes it.
Comments below suggested the use of a "Flyback Diode". Very smart idea!! This is how they work:More information: https://en.wikipedia.org/wiki/Flyback_diode I will update my schematic for this change. Brian B put it nicely in a comment below: Great content! One way to stop shocking yourself and possibly damaging you BMS, put a large diode in the opposite direction across the coil. ie negative of the diode will go to the positive coil terminal and positive of the diode to negative terminal. This is called a 'fly back' diode. And here is another super useful comment by foxabilo
Excellent Stuff !
This is a most invaluable thread here now. I was also just thinking about how to tweak things out as ATM I only have the one LFP pack but will be adding 2 more (once the Chinese holiday ends) and was pondering the complications / complexity and how to best implement a "clean solution" and this is certainly headed in the right direction. BUT I find I'm a bit confused about it (still on coffee #1, takes a pot to wake up) so I'll toss this out here @FilterGuy who obviously loves to share his knowledge & experience too. I love this place !!
Snapshot view. 1 Solar Controller, 1 Inverter/Charger, NO external LFP charger. 3 LFP packs; 1-8s2p & 2-8S, therefore 3 BMS8T to manage all 3.
* Wildcard in the deck is that I also have a large FLA bank. Using a Blue Sea 3 Way switch, so LFP = Bank 1, FLA = Bank 2, has a 1&2 combo as well.
SCC & Inverter share common 4/0 routed through a MIdnite E-Panel.
What are your suggestions / recommendation FilterGuy to configure this with the delay board ? At the moment I just have the one pack and did not install the Delay Board so it's the simple setup as shown on Page 20 with the inverter in the manual. see pic below (temporarily fugly) but I already setup the Delay Board ready to install it which I figured I'd deal with one the other packs get built. (I hate exposed boards laying around so into a box it went) My plan has been to put all the LFP Packs behind a common BUS which feeds into the 3-way switch.
Thanks for the great info !
Steve
Solarfun4jim
Solar seduced :-)
@FilterGuy
Would you mind casting your eye over this possibility(see below) and pointing out the flaws? In this way i start to get an understanding of what im doing. My assumption, was that SSR's would draw very little on the coil side, but happy for you to correct that assumption if completely wrong???Would the 0.8A from the relay control be sufficient(this is where my inexperience lets me down). I believe SSR's prefer continuous duty to switching (iirc).
Thanks
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Edited: There is a couple of problems
That looks like it would work well!
Two problems:
1) The relay would need to be 48 volt on the coils. I probably did not make that clear enough in my description. Sorry.
2) It looks like the flyback diode is backward.
A few observations.
1) With the silicone in the path, the flyback diode on the relay is very important.
2) SSR 40DD (40 amp) is overkill. They are only switching enough power to drive the relay. (~1 amp) You could use an SSR10DD (10Amp). I Did a quick search on uk amazon and found this 25 amp at a reasonably low price: https://www.amazon.co.uk/Solid-State-Relay-100DD-White/dp/B083XNSJ27/ (The description is confusing..... but I think it is 25 amp)
3) The big boat switches are overkill. They are only switching enough power to drive the relay so you could use a small 10amp toggle switch.
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I just noticed the flyback diode on the big relay looks like it is backward.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Life happens....... but not before coffee!
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Steve,
Sorry, but I am not yet picturing what you have with all of the battery banks and selector switches. Could you draw some kind of diagram?
thanks
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
It looks like the ATO.com site carries the 48 volt 200 amp version of the relay.
BTW, 200Amp @48 volt is 9600 watts. That is a hell of a lot of power for a mobile rig! What size inverter do you have?
(Could you get away with the 100 amp relay or are you just being very conservative?)
Solarfun4jim
Solar seduced :-)
It would have a 5kw inverter, looking to power an electric hob(perhaps even a twin plate)....looking at 13A 240vac(1hours daily). Doesn't leave me much to power everything else out of the max 20A ac output. I simply do not wish gas on the RV. Large battery bank(19.2kwh), use perhaps about 20-25 % capacity per day. Allowing for a couple of rainy days and not running to more than 60% of the banks total capacity. Would attempt to limit usage to less than the panels can put back in 5hours(5kw) on a sunny day.
The amperage needed for that inverter at 48v would be roughly 100. Allowing a margin of safety and peak surges, especially with a hob, i thought 200A would be in the ballpark.
Never on campsites for electric hook up, always 'boondocking' or wild camping as we like to call it.
I still fail to fathom the diode direction across the main contactor coil. I was judging it from your previous drawing. I thought it should point towards the +ve feed input(but then im easily confused....lol)
As regards "1) With the silicone in the path, the flyback diode on the relay is very important.", im not exactly sure what precisely you mean by this....mind explaining a little to this thicko...lol.
Thanks again
EDIT...looked again an i had posted a previous version.
Does this check out now?
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Looking at your diagram, the positve side is on the right. The left side goes to the load and then negative. (Or am I looking at it wrong?)
The SSRs (Solid State Relays) have some form of a silicon transistor in them (Probably a FET). All silicone transistors are much more sensitive to voltage spikes than a relay would be.
The purpose of the fly-back diode is to suppress the voltage spike that gets generated on the coil when the relay is turned off.
You may ask why is a voltage spike generated. That is a little bit complicated.
- When the DC current flows through the coil, it generates a magnetic field (It is an electro-magnet.... that is how it moves the contacts)
- When the current suddenly stops flowing, the magnetic field rapidly collapses.
- As the field collapses across the coil, it generates power with a voltage that is opposite the voltage that created the field. Since there is no current, the voltage gets very high (Power=Current*Voltage and current is zero) The only reason the voltage is not infinite is that there are other losses in the system
- When you add the diode, the revers voltage generates a current through the diode with very low resistance above ~ .7 volts. This allows a high current so the voltage stays very low.
Solarfun4jim
Solar seduced :-)
Sorry filterguy,
as regards "Looking at your diagram, the positve side is on the right. The left side goes to the load and then negative. (Or am I looking at it wrong?)"
i posted an edit at the bottom afterwards....i had posted the wrong image, now corrected.
One other aspect i thought of, at the higher amperage (40A), there would be scope to add further banks/capacity, simply by adding more bms's/SSD's in line, so very expandable.
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
The current through the main relay coil is not going to change much when you add additional SSDs. In fact, each SSD you add will create a bit of resistance that *reduces* the current ever so slightly.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Sure FilterGuy,
Current system as is logical drawing:
New Packs planned (which is what I'm trying to work out)
Current system as is logical drawing:
New Packs planned (which is what I'm trying to work out)
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