Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)


Scott SV Tengah
 

As many of you know, we've been on lithium for almost 4 years, nearly full time cruising. We noticed something about using 12v batteries in serial pairs, similar to how Amel set up the lead batteries from the outset.

We have 450AH Victron system consisting of 3 pairs of 12.8v 150AH batteries in a serial/parallel arrangement. Given that we do virtually everything on battery (cook, air-conditioning, scuba compressor, boiler, microwave, etc) with loads reasonably often in the 150-200amp range and with 200 amps of charging, I would say we're pretty tough on the batteries.

I'm taking the batteries to 100% today to top balance them properly. In each of the 3 pairs, the battery that has NEGATIVE connected to the main battery switch is the one that has lower voltage. I surmise this is because electrons flow into the positive terminal while the battery is charging and fills up the battery in each pair that has POSITIVE connected to the main battery switch. This observation is consistent across all 3 pairs and again, probably happens with lead batteries too.

I may swap the orientation of the pairs after they have been balanced out. Hope that makes sense. Probably overkill, but at nearly $11,000 USD for the batteries, I'm happy to do whatever it takes to keep them happy as I'm sure the admiral would jump ship mid passage if we had to go back to life on lead.

FYI, I do have thick copper bars between each battery in a pair. 24v batteries eliminate this problem, but the downside is that you don't have a bunch of backup engine starting batteries "built in". Once again, everything on a boat is a compromise.

--
Scott 
2007 A54 #69
SV Tengah
Currently Makemo, Tuamotus
http://www.svtengah.com


Mike Longcor (SV Trilogy)
 

Hi Scott,

Would battery balancers help? For less than 100$USD (x3) for the Victron ones, it would be a drop in the bucket for your set up. Easier to install them once instead of periodically switching battery positions and worrying about or living with imbalance. Just curious, what values did you get for voltage difference within each pair?

Cheers,
Mike Longcor
SV Trilogy SM23
Opua, NZ


On Thu, Jun 2, 2022, 8:17 AM Scott SV Tengah <Scott.nguyen@...> wrote:
As many of you know, we've been on lithium for almost 4 years, nearly full time cruising. We noticed something about using 12v batteries in serial pairs, similar to how Amel set up the lead batteries from the outset.

We have 450AH Victron system consisting of 3 pairs of 12.8v 150AH batteries in a serial/parallel arrangement. Given that we do virtually everything on battery (cook, air-conditioning, scuba compressor, boiler, microwave, etc) with loads reasonably often in the 150-200amp range and with 200 amps of charging, I would say we're pretty tough on the batteries.

I'm taking the batteries to 100% today to top balance them properly. In each of the 3 pairs, the battery that has NEGATIVE connected to the main battery switch is the one that has lower voltage. I surmise this is because electrons flow into the positive terminal while the battery is charging and fills up the battery in each pair that has POSITIVE connected to the main battery switch. This observation is consistent across all 3 pairs and again, probably happens with lead batteries too.

I may swap the orientation of the pairs after they have been balanced out. Hope that makes sense. Probably overkill, but at nearly $11,000 USD for the batteries, I'm happy to do whatever it takes to keep them happy as I'm sure the admiral would jump ship mid passage if we had to go back to life on lead.

FYI, I do have thick copper bars between each battery in a pair. 24v batteries eliminate this problem, but the downside is that you don't have a bunch of backup engine starting batteries "built in". Once again, everything on a boat is a compromise.

--
Scott 
2007 A54 #69
SV Tengah
Currently Makemo, Tuamotus
http://www.svtengah.com


Scott SV Tengah
 

Possibly, but I kept asking Victron whether their balancers were ok to use for lithium and they just kept responding “they aren’t needed”. That is clearly not true.

 

I charge with 28.4v absorption, per Victron documentation. You don’t take advantage of full capacity, but the batteries should last a lot longer. Say 20 years vs. 10 years. 😊

The positive connected battery was up to 14.31v and the negative connected one was around 13.95. For lithium, that’s a big difference and only rears its head at near full (or near empty) given the flat voltage curve. Note that I’ve only done this switching cables/copper bars one time in the last four years.

 

From: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io> on behalf of "Mike Longcor (SV Trilogy)" <svtrilogy53@...>
Reply-To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Date: Wednesday, June 1, 2022 at 11:15 AM
To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)

 

Hi Scott,

 

Would battery balancers help? For less than 100$USD (x3) for the Victron ones, it would be a drop in the bucket for your set up. Easier to install them once instead of periodically switching battery positions and worrying about or living with imbalance. Just curious, what values did you get for voltage difference within each pair?

 

Cheers,

Mike Longcor

SV Trilogy SM23

Opua, NZ

 

On Thu, Jun 2, 2022, 8:17 AM Scott SV Tengah <Scott.nguyen@...> wrote:

As many of you know, we've been on lithium for almost 4 years, nearly full time cruising. We noticed something about using 12v batteries in serial pairs, similar to how Amel set up the lead batteries from the outset.

We have 450AH Victron system consisting of 3 pairs of 12.8v 150AH batteries in a serial/parallel arrangement. Given that we do virtually everything on battery (cook, air-conditioning, scuba compressor, boiler, microwave, etc) with loads reasonably often in the 150-200amp range and with 200 amps of charging, I would say we're pretty tough on the batteries.

I'm taking the batteries to 100% today to top balance them properly. In each of the 3 pairs, the battery that has NEGATIVE connected to the main battery switch is the one that has lower voltage. I surmise this is because electrons flow into the positive terminal while the battery is charging and fills up the battery in each pair that has POSITIVE connected to the main battery switch. This observation is consistent across all 3 pairs and again, probably happens with lead batteries too.

I may swap the orientation of the pairs after they have been balanced out. Hope that makes sense. Probably overkill, but at nearly $11,000 USD for the batteries, I'm happy to do whatever it takes to keep them happy as I'm sure the admiral would jump ship mid passage if we had to go back to life on lead.

FYI, I do have thick copper bars between each battery in a pair. 24v batteries eliminate this problem, but the downside is that you don't have a bunch of backup engine starting batteries "built in". Once again, everything on a boat is a compromise.

--
Scott 
2007 A54 #69
SV Tengah
Currently Makemo, Tuamotus
http://www.svtengah.com


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Michael Winand
 

The nice thing about the  Victron Battery is that you can see what is going on with their internal voltage using the Bluetooth. 

With the lead batteries most systems would be oblivious to the difference between the two batteries in a series. 
When my ones were out I disconnected them and charged them individually. 
I had the Victron Battery balancer on my lead batteries but they didn't keep up when near end of life of the battery.
I think that this scenario of heavy use in the lead batteries is a big limiting factor.

Michael Nebo sm251 


On Thu, 2 Jun 2022, 7:56 am Scott SV Tengah, <Scott.nguyen@...> wrote:

Possibly, but I kept asking Victron whether their balancers were ok to use for lithium and they just kept responding “they aren’t needed”. That is clearly not true.

 

I charge with 28.4v absorption, per Victron documentation. You don’t take advantage of full capacity, but the batteries should last a lot longer. Say 20 years vs. 10 years. 😊

The positive connected battery was up to 14.31v and the negative connected one was around 13.95. For lithium, that’s a big difference and only rears its head at near full (or near empty) given the flat voltage curve. Note that I’ve only done this switching cables/copper bars one time in the last four years.

 

From: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io> on behalf of "Mike Longcor (SV Trilogy)" <svtrilogy53@...>
Reply-To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Date: Wednesday, June 1, 2022 at 11:15 AM
To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)

 

Hi Scott,

 

Would battery balancers help? For less than 100$USD (x3) for the Victron ones, it would be a drop in the bucket for your set up. Easier to install them once instead of periodically switching battery positions and worrying about or living with imbalance. Just curious, what values did you get for voltage difference within each pair?

 

Cheers,

Mike Longcor

SV Trilogy SM23

Opua, NZ

 

On Thu, Jun 2, 2022, 8:17 AM Scott SV Tengah <Scott.nguyen@...> wrote:

As many of you know, we've been on lithium for almost 4 years, nearly full time cruising. We noticed something about using 12v batteries in serial pairs, similar to how Amel set up the lead batteries from the outset.

We have 450AH Victron system consisting of 3 pairs of 12.8v 150AH batteries in a serial/parallel arrangement. Given that we do virtually everything on battery (cook, air-conditioning, scuba compressor, boiler, microwave, etc) with loads reasonably often in the 150-200amp range and with 200 amps of charging, I would say we're pretty tough on the batteries.

I'm taking the batteries to 100% today to top balance them properly. In each of the 3 pairs, the battery that has NEGATIVE connected to the main battery switch is the one that has lower voltage. I surmise this is because electrons flow into the positive terminal while the battery is charging and fills up the battery in each pair that has POSITIVE connected to the main battery switch. This observation is consistent across all 3 pairs and again, probably happens with lead batteries too.

I may swap the orientation of the pairs after they have been balanced out. Hope that makes sense. Probably overkill, but at nearly $11,000 USD for the batteries, I'm happy to do whatever it takes to keep them happy as I'm sure the admiral would jump ship mid passage if we had to go back to life on lead.

FYI, I do have thick copper bars between each battery in a pair. 24v batteries eliminate this problem, but the downside is that you don't have a bunch of backup engine starting batteries "built in". Once again, everything on a boat is a compromise.

--
Scott 
2007 A54 #69
SV Tengah
Currently Makemo, Tuamotus
http://www.svtengah.com


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


John Clark
 

Hi Scott,
  I too see the imbalance between first and second battery in a lithium 24v pair.  I never saw that in the AGMs.  
One thing that minimizes the imbalance for me is to limit the charge rate near end of charge.  This allows the lower voltage battery to “catch up.”

Note I am running 100ah of lithium in parallel with 300ah of agm which may make a difference. 
I charge the bank at ~ 60amp with voltage set to 28.8, when I get near -10aH left I reduce charge rate to 30amp.

Normally solar takes care of everything at a nice low rate that has me full by 1pm in St Thomas. 

Have had no capacity issues in last year and a half. 

John
SV Annie SM 37
St Thomas USVI

On Wed, Jun 1, 2022 at 5:56 PM Scott SV Tengah <Scott.nguyen@...> wrote:

Possibly, but I kept asking Victron whether their balancers were ok to use for lithium and they just kept responding “they aren’t needed”. That is clearly not true.

 

I charge with 28.4v absorption, per Victron documentation. You don’t take advantage of full capacity, but the batteries should last a lot longer. Say 20 years vs. 10 years. 😊

The positive connected battery was up to 14.31v and the negative connected one was around 13.95. For lithium, that’s a big difference and only rears its head at near full (or near empty) given the flat voltage curve. Note that I’ve only done this switching cables/copper bars one time in the last four years.

 

From: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io> on behalf of "Mike Longcor (SV Trilogy)" <svtrilogy53@...>
Reply-To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Date: Wednesday, June 1, 2022 at 11:15 AM
To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)

 

Hi Scott,

 

Would battery balancers help? For less than 100$USD (x3) for the Victron ones, it would be a drop in the bucket for your set up. Easier to install them once instead of periodically switching battery positions and worrying about or living with imbalance. Just curious, what values did you get for voltage difference within each pair?

 

Cheers,

Mike Longcor

SV Trilogy SM23

Opua, NZ

 

On Thu, Jun 2, 2022, 8:17 AM Scott SV Tengah <Scott.nguyen@...> wrote:

As many of you know, we've been on lithium for almost 4 years, nearly full time cruising. We noticed something about using 12v batteries in serial pairs, similar to how Amel set up the lead batteries from the outset.

We have 450AH Victron system consisting of 3 pairs of 12.8v 150AH batteries in a serial/parallel arrangement. Given that we do virtually everything on battery (cook, air-conditioning, scuba compressor, boiler, microwave, etc) with loads reasonably often in the 150-200amp range and with 200 amps of charging, I would say we're pretty tough on the batteries.

I'm taking the batteries to 100% today to top balance them properly. In each of the 3 pairs, the battery that has NEGATIVE connected to the main battery switch is the one that has lower voltage. I surmise this is because electrons flow into the positive terminal while the battery is charging and fills up the battery in each pair that has POSITIVE connected to the main battery switch. This observation is consistent across all 3 pairs and again, probably happens with lead batteries too.

I may swap the orientation of the pairs after they have been balanced out. Hope that makes sense. Probably overkill, but at nearly $11,000 USD for the batteries, I'm happy to do whatever it takes to keep them happy as I'm sure the admiral would jump ship mid passage if we had to go back to life on lead.

FYI, I do have thick copper bars between each battery in a pair. 24v batteries eliminate this problem, but the downside is that you don't have a bunch of backup engine starting batteries "built in". Once again, everything on a boat is a compromise.

--
Scott 
2007 A54 #69
SV Tengah
Currently Makemo, Tuamotus
http://www.svtengah.com


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Dean Gillies
 

Hi Scott,
That's an interesting observation, that the lower voltage is always found on the "bottom" battery of the pair. I can't think of a reason for that to consistently be the case.

Different batteries have slightly different capacities and the lower capacity battery will reach "full" (and empty) before the higher capacity battery. With lithium, observation of this effect by measuring the voltage will be quite pronounced at the top (and bottom) of the charge cycle.  However, if you swap the batteries around the effect should move with the battery.

Do you have anything at all attached to the midpoint terminals?
 
--
Dean Gillies
SV Stella *****,  Amel 54-154


Scott SV Tengah
 

Dean,

Nothing connected to the midpoints. Just the copper bar between the +ve and -ve on each serial pair but nothing between the midpoints of the separate pairs.

Forgive me if this is a stupid question as I'm not an engineer, but when batteries are being discharged, electrons flow from the negative terminal of each serial pair to the device doing the discharging, right ?

And when you charge, electrons are flowing from the charger to the positive terminal of each serial pair?

If the connection between the batteries in a given serial pair (copper bar with stainless bolts in my case) isn't a perfect electrical connection, the battery with the negative connection to the main battery switch suffers greater discharge under load and the battery with the positive connections to the main battery switch absorbs more electrons? Over time this would result in the imbalance I am seeing.

Would this not be similar to having unequal resistance due to different length cables, something that is frowned upon?

It is entirely possible that it's just a coincidence that the negative connected battery in all 3 serial pairs had lower voltage. I charged them individually and will let you all know the outcome after some time has passed.

On Wed, Jun 1, 2022, 18:28 Dean Gillies <stella@...> wrote:
Hi Scott,
That's an interesting observation, that the lower voltage is always found on the "bottom" battery of the pair. I can't think of a reason for that to consistently be the case.

Different batteries have slightly different capacities and the lower capacity battery will reach "full" (and empty) before the higher capacity battery. With lithium, observation of this effect by measuring the voltage will be quite pronounced at the top (and bottom) of the charge cycle.  However, if you swap the batteries around the effect should move with the battery.

Do you have anything at all attached to the midpoint terminals?
 
--
Dean Gillies
SV Stella *****,  Amel 54-154


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Dean Gillies
 

Scott,
The widely accepted model is that electrons flow one way and "holes" flow the other way in equal amounts. The current flow convention is in fact based around the flow of "holes", which flow from the positive terminal of the battery when discharging.  We engineers draw arrows representing current flow based on the movement of holes not movement of electrons.  We do this so that logical folks like you get confused! Some scientists will argue that electrons (and holes) don't actually "flow" at all, but just sort of vibrate. They do this to confuse engineers like me.

If you want to talk about flow of electrons specifically, they flow out of the negative terminal to the load and then back to the positive terminal when discharging, and they flow from the negative terminal of the charger into the negative terminal of the battery when charging.

The thing is that with two batteries in series, there is nowhere else for the current (electrons or holes) to go other than directly through each battery. Electrons and holes don't get lost on a circuit like this (unless you have a current leaking from the midpoint). Any resistive effect of the connecting busbar will happen equally to both batteries.  There is nowhere that electrons are lost in this circuit. 

The voltage difference you see is simply the result of a small difference in the effective capacity of each battery. 
When charging you drive power into the serial pair and they absorb it equally because their voltages are very close across most of the SOC range and each battery sees identical current flow. The power driven into each battery is the product of its voltage and the current flowing through it.  As the batteries reach high SOC, one of them will increase in voltage rapidly before the other one does because it is almost full before the other.  When the charger stops because the sum of the voltages reaches 28.4V the battery with the lower capacity will have a higher voltage and vice versa.

I think it is probably coincidence that your three series strings all show the same thing, and I would be expecting to see your low/high voltages swap around with the batteries.  

Regarding using a balancer... I'm not convinced that will work with Lithium.  Balancers make use of the long duration, low current end-of-charge profile of lead acid batteries. They don't balance with large currents and they don't balance quickly.
Its unlikely they could deal with the reasonably high currents which still flow near the end of a Lithium battery charge cycle. Also the voltage imbalance only occurs VERY close to the end-of-charge so the balancer does not have much time at all to try and do its job.

Looking forward to your next measurement cycle :-)
Cheers

--
Dean Gillies
SV Stella *****,  Amel 54-154


Dean Gillies
 

Scott,
John makes a couple of good points.

Each of the batteries balances itself by providing a current bypass for the cells with higher voltages, at some stage near the end of the charge cycle this process could divert current from the cells in one battery whereas the other battery will continue to charge.  By reducing the current it extends the timeline and gives the lower battery time to catch up and balance.

The other point is that John is charging to 28.8V, this will also extend the time that the cells are balancing, and thereby help reduce the imbalance in the batteries.

--
Dean Gillies
SV Stella *****,  Amel 54-154


Scott SV Tengah
 

Hi Dean,

 

Since we rarely use the generator, charging is *generally* not at high currents. Our solar is limited to 35amps and as we all know, max output is rarely held for long. If I do run the genset, I typically stop at 90% SOC, where the batteries are still well below absorption voltage and current is still at max.

 

My understand is that imbalances between batteries in a serial pair typically do not sort themselves out. This was told to me when I had gel batteries and re-iterated by Victron when I installed my lithium serial-parallel bank. While extended charge times may allow the cells within an individual 12.8v battery to equalize, it will not even out disparities between batteries in a serial pair. Victron even states that in their instructions.

 

Is Victron incorrect here?

 

From: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io> on behalf of Dean Gillies <stella@...>
Reply-To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Date: Thursday, June 2, 2022 at 4:36 AM
To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)

 

Scott,
John makes a couple of good points.

Each of the batteries balances itself by providing a current bypass for the cells with higher voltages, at some stage near the end of the charge cycle this process could divert current from the cells in one battery whereas the other battery will continue to charge.  By reducing the current it extends the timeline and gives the lower battery time to catch up and balance.

The other point is that John is charging to 28.8V, this will also extend the time that the cells are balancing, and thereby help reduce the imbalance in the batteries.

--
Dean Gillies
SV Stella *****,  Amel 54-154


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Scott SV Tengah
 

Thanks for the explanation - certainly over my pay grade, but it helps me understand where my thinking was wrong.

I'll let everyone know if the high/low voltages swap around with the batteries.

Regarding the balancer, do you think my use-case is a bit different and therefore it may make sense to include a balancer? It is extremely rare that I run the genset to charge to 100%. Typically I stop at 90%, when cell voltages are still far from the upper "knee" and just let the solar do the rest. I do notice that if I pump 200amps in to the batteries until full, the battery temp (Victron batteries report temp via bluetooth) increases a lot more than if I reduce this tail current. And knowing that lithium don't love heat combined with high SOC, I avoid it.

In any event, I wonder if the much lower currents and longer duration of solar top balancing gives the balancers enough time to do their magic?




--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Dean Gillies
 

Scott,
I'm still not convinced a balancer will help. 

I suspect your batteries will not show much imbalance if you check them at lower states of charge. The balancer only has time to do its job at the top end when the voltage of one battery kicks up before the other.  Maybe you can check this and log the imbalance at different states of charge. If your batteries are out of balance across the entire SOC range then maybe there is a case for an external balancer.

Series-connected lead batteries will definitely not self-balance, and will get progressively worse on each cycle.

Series-connected lithium batteries may try to self-balance, it depends upon how the cell balancing is configured. The cell-balancers provide an amount of bypass current which effectively does not (over)charge that battery, but will contribute charge to a second (lower voltage) battery.  The problem is that the bypass currents are very small, and only start when the first battery is almost fully charged so there is not enough time to bring the second battery up quickly enough.  So in practical terms the effect will not solve an imbalance problem.

Solar top balancing will help but timing is a problem. My bank takes about 4-5hours to fully balance after the pack reaches the balancing start voltage, and this only really happens in practice when on shore power.
  

--
Dean Gillies
SV Stella *****,  Amel 54-154


Jose Venegas
 

Scott,
I agree with Dean. Independent of the band, it makes sense that controlling the total voltage of a battery set in series does not ensure that the voltage of both batteries is sufficient to trigger balancing in both. The victron balancer does the trick. I spoke about it to a technician of Battle borne and he agreed with its use. I used to have differences greater than 2% between the two battery voltages of one set during the final part of charging to 100%. Since I installed the balancer the differences have been around 0.1 and 0.2%. I have 4 sets of two 12V 100 ah lithium batteries in series with one balancer.

Jose Venegas
Ipanema SM2K 278
Cartagena


Mike Longcor (SV Trilogy)
 

I might be stating the obvious here but unless battery midpoints are interconnected, you will need one balancer per battery pair. They start doing their job when voltage is above 27.3V. For their price, I think they are worth it for any 24V system using 12V battery pairs.

Cheers,
Mike

On Sat, Jun 4, 2022, 10:41 AM Jose Venegas via groups.io <josegvenegas=icloud.com@groups.io> wrote:
Scott,
I agree with Dean.  Independent of the band, it makes sense that controlling the total voltage of a battery set in series does not ensure that the voltage of both batteries is sufficient to trigger balancing in both.  The victron balancer does the trick. I spoke about it to a technician of Battle borne and he agreed with its use.  I used to have differences greater than 2% between the  two battery voltages of one set during the final part of charging to 100%.  Since I installed the balancer the differences have been around 0.1 and 0.2%.   I have 4 sets of two 12V 100 ah lithium batteries in series with one balancer.

Jose Venegas
Ipanema SM2K 278
Cartagena





Scott SV Tengah
 

Dean,

Well it seems there's theory and then there's practice. Or something else is going on.

First measurement after swapping the wiring of each respective serial pair such that the prior "bottom" battery that was previously connected to "negative" battery switch was now made into a "top" battery that is now connected to "positive". And of course vice versa.

For ALL three separate pairs, the new "top" battery exhibits higher voltage than the "bottom" battery at the end of charging. The difference is anywhere from 0.03v to 0.28v. So it was not just a coincidence. 

I may need to have more conversations with Victron about the balancer. If I run the genset in the morning to take my batteries to 100%, the energy balance will remain positive for most of the day, allowing them to work. This should be more than the 4-5 hours that your batteries need to balance out.

Thoughts?



 On Thu, Jun 2, 2022 at 10:17 AM, Dean Gillies wrote:

Looking forward to your next measurement cycle :-)
Cheers

--
Dean Gillies
SV Stella *****,  Amel 54-154

 
--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Dean Gillies
 

Hi Scott,
Well there you go. I don't understand the mechanism whereby the bottom battery is consistently lower voltage.
Sounds like an interesting conversation with Victron.
Keep us posted on what they say.

Out of interest I just checked my old notes from AGM batteries when I was looking at balancers a few years ago. I had 6 strings, and 4 of them had the TOP battery at higher voltage and 2 had the bottom battery at higher voltage. As I type, my Lead batteries are showing the TOP battery as being higher - see pic.

--
Dean Gillies
SV Stella *****,  Amel 54-154


Dean Gillies
 

.. and its been this way for some time ...
--
Dean Gillies
SV Stella *****,  Amel 54-154


Jose Venegas
 

Mike
I use one balancer with the battery midpoints interconnected as required by Victron 

Jose Gabriel Venegas
Ipanema SM2k 278