Parallel and Series Cells for redundancy

[Windseeker]

It's time... My AGM bank is getting long in the tooth and time to retire.


I'm reading as much as I can on the installation and it looks really straight forward with a few caveats.


I was reading an older post about parallel and series battery connections with pictures, but the pics were no longer there. I like the idea of multiple cells to give some level of redundancy for the house systems bank. I am thinking there are two options for connecting these cells. I am thinking either will work with Option B being preferred.



Is there a consensus on this?


Thank you!



Mark

[dougweibel]

The way you have thing arranged in your A and B there is no difference electrically and there is no redundancy provided other than there is an extra cable connecting each parallel pair of batteries to the next pair in series. Failure of a battery cable is a pretty rare event. I don't see much value in B over A. If you are really a "belt and suspenders" person you'd want to use B and double the top and bottom cables in the figure as well.

[Windseeker]

Thank you for the input. Just making sure I wasn't missing something on the onset of this project as I work my way inside out.


Option A will actually work better in the space allocated. Glad to know there is no significant penalty.



Very much appreciated!Mark

[T1 Terry]

Option A works best, option B doesn't force both cells to work together because all the current comes in one end of both cells and out the other. One cell is the closest (shortest electrical path) on the way in and the other cell is the closest on the way out ..... no matter if you are charging or discharging.


T1 Terry

[Windseeker]

Hi Terry!

I'm a huge T1 Terry fan!

I've been inspired to do this conversion with the reading of the "House Bank" thread started by Sytaniwha back on 2011-07-28. You and so many others have made significant contributions to that thread. It is very much appreciated. Someone called it "Magic Help" and I could not agree more. I have read through the first 800 posts and have a solid understanding of how to treat these batteries so I don't kill them.

The attached PDF is more or less how this boat is laid out today. I understand very well that many things will have to change to adopt these batteries. I have a design on my hard drive that I won't share just yet because the following question will influence that design.

The way Catalina designed it was to have a 4D house battery and a 4D reserve battery. After killing two SLA batteries over the first 2 seasons of owning the boat, I switched to AGMs from SLAs and ran the packs under BOTH selector with a reserve Jump Pack on board. This was the right call as I never had a start issue and never needed the jump pack.

Going forward, I am thinking of separating the two to have a separate AGM Engine Start circuit from the LiFePO4 House Bank. I can do this because this LiFePO4 pack will have the same capacity as the two 4D AGM. I will not need to combine them anymore. There are two ways I could implement this. 1)Start the Engine with the LiFePO4 and trickle charge the reserve AGM to keep it full or 2) dedicate the AGM to 100% engine start and bring in the LiFePO4 in on emergency start situation.

Now is the time to make this modification. What is the best practice here?

Many Thanks,

Mark

[T1 Terry]

Something that might help with lithium house battery understanding is a website my wife Margaret wrote and updates regularly with new bits as she gets her head around my garbled techno-speak and converts it into plain speak :lol: t1lithium.com.au It is her business, I'm just the flogged redheaded step child that does the work for no pay ... but the benefit package is good .......

Looking at your PDF, are you planning to replace one of the AGM's with the lithium battery pack?

Two ways to do it, use an Electrodacus BMS that has the ability to separately switch charging on/off and also non essential loads off when the capacity gets low before actually isolating the lithium battery if it gets down to the potential damage level. You would then need to switch in the start battery to supply the essential loads once you started the engine so recharging was occurring before you switched the essential loads and non essential loads back on as the battery condition improved.

The other method is to "T" the lithium battery into the existing AGM supply and use an isolator to disconnect the lithium battery if a cell went either high or low voltage so there were no voltage spikes, the AGM will act as a capacitor to absorb any potentially damaging spikes.

A hybrid of the "T" in method and the Electrodacus SBMS-0 BMS where the charging and the load both are connected to the AGM battery and via either big solid state relays or contactors controlled by the SBMS-0 to isolate the lithium battery from the AGM battery.
In this design, the AGM battery is really only there as a capacitor, the lithium runs at a higher voltage than the AGM but not higher than the AGM charging voltage, so basically the AGM battery remains in float charging mode but takes the current surge when the lithium cuts the charging and the back EMF voltage spike when the high induction loads are disconnected but the lithium battery has been isolated due to low cell voltage.
Also, using this method all the existing charging devices can be set to AGM so no special charges are required .... not that the lithium charging regime in any of them actually suits lithium batteries, but the ability to operate at maximum output for long periods is a necessity, so if they are rated for lithium at least you know they should be built to take the punishment.

As a side note, if a charger says it is suited to a limited lead acid battery capacity, they are basically saying it is not 100% continuous output rated, the max output is a distortion of the facts and it will let the smoke out if it gets pushed that hard ..... So I suppose there is such a thing as a lithium suitable battery charger, it is one where the manufacturer is honest about the maximum continuous output

Yeah, as usual, no short simple answer eh

T1 Terry

[grizzman]

Originally Posted by T1 Terry

Something that might help with lithium house battery understanding is a website my wife Margaret wrote and updates regularly with new bits as she gets her head around my garbled techno-speak and converts it into plain speak :lol: t1lithium.com.au It is her business, I'm just the flogged redheaded step child that does the work for no pay ... but the benefit package is good .......

Looking at your PDF, are you planning to replace one of the AGM's with the lithium battery pack?

Two ways to do it, use an Electrodacus BMS that has the ability to separately switch charging on/off and also non essential loads off when the capacity gets low before actually isolating the lithium battery if it gets down to the potential damage level. You would then need to switch in the start battery to supply the essential loads once you started the engine so recharging was occurring before you switched the essential loads and non essential loads back on as the battery condition improved.

The other method is to "T" the lithium battery into the existing AGM supply and use an isolator to disconnect the lithium battery if a cell went either high or low voltage so there were no voltage spikes, the AGM will act as a capacitor to absorb any potentially damaging spikes.

A hybrid of the "T" in method and the Electrodacus SBMS-0 BMS where the charging and the load both are connected to the AGM battery and via either big solid state relays or contactors controlled by the SBMS-0 to isolate the lithium battery from the AGM battery.
In this design, the AGM battery is really only there as a capacitor, the lithium runs at a higher voltage than the AGM but not higher than the AGM charging voltage, so basically the AGM battery remains in float charging mode but takes the current surge when the lithium cuts the charging and the back EMF voltage spike when the high induction loads are disconnected but the lithium battery has been isolated due to low cell voltage.
Also, using this method all the existing charging devices can be set to AGM so no special charges are required .... not that the lithium charging regime in any of them actually suits lithium batteries, but the ability to operate at maximum output for long periods is a necessity, so if they are rated for lithium at least you know they should be built to take the punishment.

As a side note, if a charger says it is suited to a limited lead acid battery capacity, they are basically saying it is not 100% continuous output rated, the max output is a distortion of the facts and it will let the smoke out if it gets pushed that hard ..... So I suppose there is such a thing as a lithium suitable battery charger, it is one where the manufacturer is honest about the maximum continuous output

Yeah, as usual, no short simple answer eh

T1 Terry

Hi ya Terry!
One thing that I would like to add is if your using the ElectroDacus SBMS0 and a DSSR20 with diversion can send solar to a SCC set for FLA (in my case)

[T1 Terry]

Originally Posted by grizzman

Hi ya Terry!
One thing that I would like to add is if your using the ElectroDacus SBMS0 and a DSSR20 with diversion can send solar to a SCC set for FLA (in my case)

Yes, but you need a few of them if you have much solar. Most of the systems we build/install are above 50 amps and the best so far was just over 300 amps @ 24v nom. A better method might be to use the diversion control to switch bigger solid state relays or contractors so the solar can go to different controllers. Another option is to use the charge cut output to switch an MPPT controller off or just feed the MPPT output to a diode charging splitter (real old technology) and cut the charging leg to the lithium battery using a relay or contactor so all the output now goes to the lead acid battery. So many ways to skin the same cat :lol:

The Electrodacus unit will need to be mounted in a well sealed box to keep the salt spray out of it, but the Bluetooth output has a good range so it wouldn't be necessary to open the box very often.

T1 Terry

[grizzman]

Originally Posted by T1 Terry

Yes, but you need a few of them if you have much solar. Most of the systems we build/install are above 50 amps and the best so far was just over 300 amps @ 24v nom. A better method might be to use the diversion control to switch bigger solid state relays or contractors so the solar can go to different controllers. Another option is to use the charge cut output to switch an MPPT controller off or just feed the MPPT output to a diode charging splitter (real old technology) and cut the charging leg to the lithium battery using a relay or contactor so all the output now goes to the lead acid battery. So many ways to skin the same cat :lol:

The Electrodacus unit will need to be mounted in a well sealed box to keep the salt spray out of it, but the Bluetooth output has a good range so it wouldn't be necessary to open the box very often.

T1 Terry

Thanks Terry, just one correction. It uses WiFi not Bluetooth.

[T1 Terry]

Originally Posted by grizzman

Thanks Terry, just one correction. It uses WiFi not Bluetooth.

Ahhh.... well that answers one problem :lol: One of the Betta systems we installed seemed to working fine but the customer says he can see the Victron apps but not the Electrodacus .... didn't click that they were looking for it with the WiFi turned off, that seems to be the only way the Bluetooth will work on a smart phone .... I'll try that theory next time we hear from them, so a big thank you in advance ....

T1 Terry

[Windseeker]

Hi Terry,

First of all, Congratulations on opening your business! I went through your website and found it very informative. You are very passionate about this technology and wish you much success and happiness in your endeavor. Can you still get the Junsi Cell logger? It was obsolete when I went shopping for cell meters.

I received my batteries in Feb and conducted different tests with the PowerMax Charger and loaded the batteries with an inverter and a space heater. As you mentioned before, after about 13.7 volts, very little amp hours go into the battery and the cell voltage begins to climb. I found that the 3 stage charger doesn't kick in unless you push the voltage up to at least 14.2. At 14.4V, it was pushing the some cells slightly north of 3.6V which is more than the 3.45 you mentioned is optimal. For now, I set it to fixed voltage at 13.8 since this is a safe rate. The Question I have on this is how much damage is actually being done with the batteries charged to 14.4? The current was in the milliamp range with the batteries being full. The ISDT cell meter only reports 93% capacity at 13.8 volts. You have to push the voltage to 14.4 before it thinks its full. Plus, I am only charging at around a 40 amp rate on my 100 (80 actually) amp charger with it throttled back to 13.8 volts.

I have come up with a preliminary design on how I might install these batteries on this system. I will finally have enough House Bank capacity that I can separate and have a dedicated engine start battery. I have always been told this is the way to do it.

I did not mention that I purchased a Sterling advanced alternator regulator many years ago but never got around to installing it and was not sure if I was going to with this change. Same for the Link Lite AH meter. I think the Link Lite will be helpful and the ability to isolate the alternator field wire with the Sterling is a big plus if there is any hint of overcharging. Plus, there is battery and alternator temp monitoring.

I did not need to buy many parts to piece this together. I will be the BMS for the most part. What I care most about is disconnecting the fridge load if I am away from the dock and not kill the batteries. There is no harm in keeping the shore charger at 13.8V from my understanding. The secondary concern would be not killing the alternator or batteries if at the helm for 6 hours motoring.

Any comments on my proposed layout is very much appreciated.

Sincerely,

Mark

[rgleason]

Terry's website. T1lithium. Com au

https://www.t1lithium.com.au/about-us.html