DC to DC charger behavior

[grizzzman]

OK. Thanks. I installed the overkill app and it provides much more insight into the BMS set up. Excellent recommendation!

Interestingly the internal BMS settings indicate BMS sees 100% SOC at 3.35V. that seems a bit low vs some other numbers I have seen. Not sure what to make of that. The good news is both the overkill and the ecoworthy app indicate cells are well balanced.

There is really no point in balancing below 3.4. Balancing is really needed as cells diverge and even then it becomes a game of diminishing returns.

I am not sure there is much difference in terms of practical power capacity between, say 3.35 and 3.45 V so I may be obsessing over nothing?

It really depends on how much of the AH's you paid for that you want to use.

 

[singlehander]

There is really no point in balancing below 3.4. Balancing is really needed as cells diverge and even then it becomes a game of diminishing returns.

It really depends on how much of the AH's you paid for that you want to use.

Yes. Understand second paragraph. The issue is I do not know how many AH I am giving up. I would like to use as many as possible.

If 10 ah no problem.
If 50 ah ...problem.

I am just very skittish about charging my new 280 ah LFP without knowing how full the tank is. Should I just say the heck with it and keep charging at 14.6 V until the cells come up to 3.45 or 3.65? BMS says it's cutoff is 3.7 V so do the cognoscenti simply depend upon the BMS to terminate charging, at least first time around, so I can establish where "full" is for both me and my shunt equipped battery monitor?

 

[grizzzman]

Yes. Understand second paragraph. The issue is I do not know how many AH I am giving up. I would like to use as many as possible.

If 10 ah no problem.
If 50 ah ...problem.

I am just very skittish about charging my new 280 ah LFP without knowing how full the tank is. Should I just say the heck with it and keep charging at 14.6 V until the cells come up to 3.45 or 3.65? BMS says it's cutoff is 3.7 V so do the cognoscenti simply depend upon the BMS to terminate charging, at least first time around, so I can establish where "full" is for both me and my shunt equipped battery monitor?

My suggestion would be to condition the battery. As an example I purchased 2 cheep Temu 100 AH batteries. 218.00 for Both. Paralleled them put the power supply on at 14.6 once it hit the wall the amps/watts meters were on/off/on etc. This told me one battery was disconnected and the other battery was on the edge. Let them sit overnight to allow balancing to continue. Discharged for a while. Charged to 14.2 without disconnect. Discharged. 14.4 then 14.6 without disconnect. If you think that the batteries come truly balanced? Guess what, not likely. On a side note my diy 12 cell 8 year old LFP was paralleled with a 12 volts FLA GC2 bank for seven years. I would not recommend this on a boat. Good luck on your project!

 

[singlehander]

My suggestion would be to condition the battery. As an example I purchased 2 cheep Temu 100 AH batteries. 218.00 for Both. Paralleled them put the power supply on at 14.6 once it hit the wall the amps/watts meters were on/off/on etc. This told me one battery was disconnected and the other battery was on the edge. Let them sit overnight to allow balancing to continue. Discharged for a while. Charged to 14.2 without disconnect. Discharged. 14.4 then 14.6 without disconnect. If you think that the batteries come truly balanced? Guess what, not likely. On a side note my diy 12 cell 8 year old LFP was paralleled with a 12 volts FLA GC2 bank for seven years. I would not recommend this on a boat. Good luck on your project!

Yea, I was suspicious about the balance too given all the discussion here about balancing and how imbalance is very common esp on cheapos.

I think I can follow your process. I don't plan to use a power supply per se but I can set up my Victron DC to DC charger to do the job. It is actually set up already because I have tweaked the LFP setting to 16.6 Volts. I will charge using a 20 amp shore power charger through the Victron. The Victron output Voltage is easy to configure as you probably know,

The other alternative is to go ahead and use a bench power supply I possess but it does not sound like I need to hassle with temporarily rewiring the system and dragging the PS to the boat just to use a stand alone PS vs Victron.

Regardless, what you are telling me is I don't need to worry about overcharge because the BMS will trip before any overcharging occurs and that, long term, I can leave my single battery charging at 14.6 V safely. During my initial conditioning If the batt is imbalanced the BMS will trip, I do some discharge and I just back Volts off to, say 14.2 and go again, if no trips at that Voltage, do another discharge and up it .2Volts (14.4) and go again rinse and repeat until the battery can take 16.5 Volts.

Is that correct?

 

[yabert]

until the battery can take 16.5 Volts.

Is that correct?

No. 16.5 is way to high for a 4 cells lfp.
14.6V is the maximum and you can set to charge at 14.0-14.2V range without problem.

 

[grizzzman]

Yea, I was suspicious about the balance too given all the discussion here about balancing and how imbalance is very common esp on cheapos.

I think I can follow your process. I don't plan to use a power supply per se but I can set up my Victron DC to DC charger to do the job. It is actually set up already because I have tweaked the LFP setting to 16.6 Volts. I will charge using a 20 amp shore power charger through the Victron. The Victron output Voltage is easy to configure as you probably know,

The other alternative is to go ahead and use a bench power supply I possess but it does not sound like I need to hassle with temporarily rewiring the system and dragging the PS to the boat just to use a stand alone PS vs Victron.

Regardless, what you are telling me is I don't need to worry about overcharge because the BMS will trip before any overcharging occurs and that, long term, I can leave my single battery charging at 14.6 V safely. During my initial conditioning If the batt is imbalanced the BMS will trip, I do some discharge and I just back Volts off to, say 14.2 and go again, if no trips at that Voltage, do another discharge and up it .2Volts (14.4) and go again rinse and repeat until the battery can take 16.5 Volts.

Is that correct?

Well no. Most is yes but where did you get the 16.5 volt number from? The BMS will trip somewhere around 14.75. If there is an issue with the BMS you will very likely degrade ( or worse depending on absorption time ) for the purpose of conditioning the battery go no higher than 3.65 volts per cell. As far as in use voltage as an example if you cap voltage to 14.2 but you will need a longer absorption time then say at 14.5 volts.

 

[tpenfield]

FWIW - I designed my marine system to be able to charge the LFP batteries from 3 sources.

Solar
Alternator (via the DC-DC charger)
Shore power (via the Xantrex Inverter)

I do have a solar lockout so that the solar charge controller and the DC-DC charger are not trying to manage the charging cycle simultaneously, when the engines are running.

When on shore power, I figure the Xantrex, being more powerful, will rule the day. Most the time I am on shore power is at night, so the solar is sleeping.

Anyway . . . I set the charging rate on the Xantrex to be fairly low (like 20 amps) and the DC-DC charger is fairly low as well so as not to over load the alternators. BTW - if you have one of the newer digitally controlled marine engines (either outboard or inboard) you are best not to be charging from the alternators when the engine RPM is fairly low (idle/no-wake speeds). The DC-DC charger will try to go into Bulk charging mode and drag the voltage down to a point where the digital control system starts throwing out alerts and may even shut the engine(s) down (BTDT). I added an activation setting to the DC-DC charger to only activate if the input voltage was at a high enough level.

 

[singlehander]

Well no. Most is yes but where did you get the 16.5 volt number from? The BMS will trip somewhere around 14.75. If there is an issue with the BMS you will very likely degrade ( or worse depending on absorption time ) for the purpose of conditioning the battery go no higher than 3.65 volts per cell. As far as in use voltage as an example if you cap voltage to 14.2 but you will need a longer absorption time then say at 14.5 volts.

Sorry about that. I meant 14.6 volts. That is what is stipulated by the battery mfg.

According to overkill solar, the internal jbd BMS is configured to trip at cell voltage of 3.75 V and to reset at 3.6.

Meanwhile. The BMS SOC is set to show 100% SOC at 3.35 V which seems a bit low?

Anyway. Today I tried to charge to 3.65 V and boy did those imbalances come into view as voltages came up. I have one cell that is way out of school. About 110mv above the lowest cell. The high cell was at 3.65 v (charging). When I reached this voltage I shut it down rather than depend upon BMS.

Given the above, is the strategy to simply allow the bat to discharge some and then repeat the charge cycle until such time as the cells balance? I do note overkill solar is telling me the hi cells are balancing so something is happening.

 

[grizzzman]

Sorry about that. I meant 14.6 volts. That is what is stipulated by the battery mfg.

According to overkill solar, the internal jbd BMS is configured to trip at cell voltage of 3.75 V and to reset at 3.6.

Meanwhile. The BMS SOC is set to show 100% SOC at 3.35 V which seems a bit low?

Anyway. Today I tried to charge to 3.65 V and boy did those imbalances come into view as voltages came up. I have one cell that is way out of school. About 110mv above the lowest cell. The high cell was at 3.65 v (charging). When I reached this voltage I shut it down rather than depend upon BMS.

Given the above, is the strategy to simply allow the bat to discharge some and then repeat the charge cycle until such time as the cells balance? I do note overkill solar is telling me the hi cells are balancing so something is happening.

Bring the voltage down say 14.0 to start. The idea is to slow down the runner to allow more time balancing at a higher voltage. Then repeat. In between leave it at the higher voltage overnight. Draw it down, etc

 

[singlehander]

FWIW - I designed my marine system to be able to charge the LFP batteries from 3 sources.

Solar
Alternator (via the DC-DC charger)
Shore power (via the Xantrex Inverter)

I do have a solar lockout so that the solar charge controller and the DC-DC charger are not trying to manage the charging cycle simultaneously, when the engines are running.

When on shore power, I figure the Xantrex, being more powerful, will rule the day. Most the time I am on shore power is at night, so the solar is sleeping.

Anyway . . . I set the charging rate on the Xantrex to be fairly low (like 20 amps) and the DC-DC charger is fairly low as well so as not to over load the alternators. BTW - if you have one of the newer digitally controlled marine engines (either outboard or inboard) you are best not to be charging from the alternators when the engine RPM is fairly low (idle/no-wake speeds). The DC-DC charger will try to go into Bulk charging mode and drag the voltage down to a point where the digital control system starts throwing out alerts and may even shut the engine(s) down (BTDT). I added an activation setting to the DC-DC charger to only activate if the input voltage was at a high enough level.

Thanks for this overview.

I am in a small 30 foot single engine sailboat. My engine, a Yan 2GM20F, is 38 years old so no electronics. I am equipped with a large externally regulated 125 amp alternator on a serpentine belt. I also have both my regulator and DC to DC charger limited to 40 amps so with charging and equipment loading underway I am around 55 amps total. I have yet to test alternator charging but am well aware of the long run time high amp heat risk so I will be watching this carefully and will squeeze current down further if necessary.

My current set up is solar direct to the LFP battery. Neither Shore nor regulator have a lithium program so they charge the AGM start and feed a DC to DC charger then to the LFP.

The concept of solar controller and DC to DC charger competing for the charge cycle is not something I have considered. How did you implement the lockout? In my config the DC to DC charger will conflict with solar at the dock AND motoring underway. Maybe when either are "true" I should just turn my solar off?

 

[singlehander]

FWIW - I designed my marine system to be able to charge the LFP batteries from 3 sources.

Solar
Alternator (via the DC-DC charger)
Shore power (via the Xantrex Inverter)

I do have a solar lockout so that the solar charge controller and the DC-DC charger are not trying to manage the charging cycle simultaneously, when the engines are running.

When on shore power, I figure the Xantrex, being more powerful, will rule the day. Most the time I am on shore power is at night, so the solar is sleeping.

Anyway . . . I set the charging rate on the Xantrex to be fairly low (like 20 amps) and the DC-DC charger is fairly low as well so as not to over load the alternators. BTW - if you have one of the newer digitally controlled marine engines (either outboard or inboard) you are best not to be charging from the alternators when the engine RPM is fairly low (idle/no-wake speeds). The DC-DC charger will try to go into Bulk charging mode and drag the voltage down to a point where the digital control system starts throwing out alerts and may even shut the engine(s) down (BTDT). I added an activation setting to the DC-DC charger to only activate if the input voltage was at a high enough level.

Thanks for this overview.

I am in a small 30 foot single engine sailboat. My engine, a Yan 2GM20F, is 38 years old so no electronics. I am equipped with a large externally regulated 125 amp alternator on a serpentine belt. I also have both my regulator and DC to DC charger limited to 40 amps so with charging and equipment loading underway I am around 55 amps total. I have yet to test alternator charging but am well aware of the long run time high amp heat risk so I will be watching this carefully and will squeeze current down further if necessary.

My current set up is solar direct to the LFP battery. Neither Shore nor regulator have a lithium program so they charge the AGM start and feed a DC to DC charger then to the LFP.

The concept of solar controller and DC to DC charger competing for the charge cycle is not something I have considered. How did you implement the lockout? In my config the DC to DC charger will conflict with solar at the dock AND motoring underway. Maybe when either are "true" I should just turn my solar off?

 

[wholybee]

Thanks for this overview.

I am in a small 30 foot single engine sailboat. My engine, a Yan 2GM20F, is 38 years old so no electronics. I am equipped with a large externally regulated 125 amp alternator on a serpentine belt. I also have both my regulator and DC to DC charger limited to 40 amps so with charging and equipment loading underway I am around 55 amps total. I have yet to test alternator charging but am well aware of the long run time high amp heat risk so I will be watching this carefully and will squeeze current down further if necessary.

My current set up is solar direct to the LFP battery. Neither Shore nor regulator have a lithium program so they charge the AGM start and feed a DC to DC charger then to the LFP.

The concept of solar controller and DC to DC charger competing for the charge cycle is not something I have considered. How did you implement the lockout? In my config the DC to DC charger will conflict with solar at the dock AND motoring underway. Maybe when either are "true" I should just turn my solar off?

You can have multiple chargers of different types charging a battery at the same time. There is no issue. As the battery approaches full, one charger might drop to float before the others, but it doesn't hurt anything and doesn't slow charging, as the battery is nearly full and not accepting current anyway.

 

[singlehander]

You can have multiple chargers of different types charging a battery at the same time. There is no issue. As the battery approaches full, one charger might drop to float before the others, but it doesn't hurt anything and doesn't slow charging, as the battery is nearly full and not accepting current anyway.

Thanks for clarification.

 

[singlehander]

So I took a run at balancing the cells yesterday. I got the high cell to 3.65 V and, at that point, it was about 120MV above the lowest cell. I did not wait for the BMS to trip, I just turned charging off. The overkill application indicated cells were balancing so I just let the battery do its thing for 24 hours. I went down to the boat again today and charged the battery again. The imbalance was down to 60 millivolts so I am very encouraged that balancing is actually taking place. I will be doing a third cycle tomorrow and I hope this will show things are continuing to move in the right direction.

Meanwhile both the overkill and the OEM app are indicating SOC at 278 - 280 (99-100%) even though I know I have discharged as much as 27 AH and this is supported by declining cell voltages. The SOC appears to be stuck. I am reaching out to Ecoworthy on this issue, hopefully there is an easy fix. A return will be a giant PIA.

 

[grizzzman]

So I took a run at balancing the cells yesterday. I got the high cell to 3.65 V and, at that point, it was about 120MV above the lowest cell. I did not wait for the BMS to trip, I just turned charging off. The overkill application indicated cells were balancing so I just let the battery do its thing for 24 hours. I went down to the boat again today and charged the battery again. The imbalance was down to 60 millivolts so I am very encouraged that balancing is actually taking place. I will be doing a third cycle tomorrow and I hope this will show things are continuing to move in the right direction.

Looks like you are on the right track.

Meanwhile both the overkill and the OEM app are indicating SOC at 278 - 280 (99-100%) even though I know I have discharged as much as 27 AH and this is supported by declining cell voltages. The SOC appears to be stuck. I am reaching out to Ecoworthy on this issue, hopefully there is an easy fix. A return will be a giant PIA.

Do not get too hung up on the 100% thing. End voltage, absorption time and end amps are the real decider of SOC.

 

[wholybee]

So I took a run at balancing the cells yesterday. I got the high cell to 3.65 V and, at that point, it was about 120MV above the lowest cell. I did not wait for the BMS to trip, I just turned charging off. The overkill application indicated cells were balancing so I just let the battery do its thing for 24 hours. I went down to the boat again today and charged the battery again. The imbalance was down to 60 millivolts so I am very encouraged that balancing is actually taking place. I will be doing a third cycle tomorrow and I hope this will show things are continuing to move in the right direction.

Meanwhile both the overkill and the OEM app are indicating SOC at 278 - 280 (99-100%) even though I know I have discharged as much as 27 AH and this is supported by declining cell voltages. The SOC appears to be stuck. I am reaching out to Ecoworthy on this issue, hopefully there is an easy fix. A return will be a giant PIA.

The overkill BMS (and most, in fact) are not accurate until a couple full charge/discharge cycles. During setup, balancing, and the first cycles of operation, it only makes a best guess while it calibrates. It uses both the voltages stored in the BMS, and the Ah counter to do this.

Incidentally, if you were to set your charger to only charge to (for example) 13.9V, the BMS would learn this, and start considering that as 100%.

 

[singlehander]

Griz and wholly, you are correct. Once I finally got the battery fully charged based upon cell voltages and then began a load test, the BMS began to register what appears to be a fairly accurate representation of SOC. I am checking cell voltages against a hardcopy "SOC vs cell voltage" chart and am tracking this pretty well as the battery discharges. I am into the third day of testing (low amp load) and the battery is at around 45% SOC so definitely in the ballpark when I do the math on time vs amps( in addition to just looking at cell voltages vs SOC on the chart).

It seems like getting the batt to full charge was the key to getting the BMS squared away on SOC reporting as you guys suggested it would.