Problem with Balmar Mc614 and LiFeP04

[twistedtree]

Does this mean it can be hooked up?

Yes, the Wakespeed has an input for a battery shunt, if you choose to install one.

 

[Jeff F]

That's interesting, and different from what I see and described in a previous post. What setup behaves this way? The chargers I have used seem to hold the SOC pretty well just by regulating float voltage. As discussed, it's a bit of a crap shoot just what SOC you will get for any given float voltage, but whatever it is, my stuff seems to hold it pretty well.

I'm going to argue based on what you've described that your charge cycle is stopping before is has to. You're charging to what would be 90% of a more aggressive approach and calling it 100%.

By definition if a 13.5v float maintains a 100% SoC with load it indicates that your SoC calibration is out of whack. That's my theory. Your 100% could correspond to someone else's 85-90%.

I could turn this around - if you start with a dead battery and charge with 13.5v until current reaches zero, what will the SoC be? It's not going to be 100% of the possible maximum charge.

 

[twistedtree]

I'm going to argue based on what you've described that your charge cycle is stopping before is has to. You're charging to what would be 90% of a more aggressive approach and calling it 100%.

By definition if a 13.5v float maintains a 100% SoC with load it indicates that your SoC calibration is out of whack. That's my theory. Your 100% could correspond to someone else's 85-90%.

I could turn this around - if you start with a dead battery and charge with 13.5v until current reaches zero, what will the SoC be? It's not going to be 100% of the possible maximum charge.

Initial bulk charge to higher than13.5. I don't remember exactly, but 13.8 sticks in my head, and that only brings the batteries to about 95%. After it hit hits 14V it drops to float at 13.5. And that 13.5V slowly keeps charging the batteries until they get to 100%.

And that's just for the alternator. Other chargers controlled by DVCC run up to 14V, then float about 13.5V, all under BMS control.

 

[Jeff F]

Initial bulk charge to higher than13.5. I don't remember exactly, but 13.8 sticks in my head, and that only brings the batteries to about 95%. After it hit hits 14V it drops to float at 13.5. And that 13.5V slowly keeps charging the batteries until they get to 100%.

And that's just for the alternator. Other chargers controlled by DVCC run up to 14V, then float about 13.5V, all under BMS control.

Right. By using 13.8 you're leaving ~10% of capacity on the table. If you were more aggressive with the top charge you'd never see that behaviour. Again, it's a question of where you mark your 100%.

 

[twistedtree]

Right. By using 13.8 you're leaving ~10% of capacity on the table. If you were more aggressive with the top charge you'd never see that behaviour. Again, it's a question of where you mark your 100%.

OK, I'm not following. Let's say my bulk charge was to 14V. What behavior would you then expect to see with a float of 13.5V?

 

[Jeff F]

OK, I'm not following. Let's say my bulk charge was to 14V. What behavior would you then expect to see with a float of 13.5V?

Approach this as a calibration challenge. I'd posit that since you've never tried significantly higher thresholds (not just voltage, but termination as well) you don't really know where 100% is on your pack. That's fine.

I can tell you that when I charge my drop-in pack to the max recommended 14.6v and leave the rest to the charger defaults my SoC under use will drop to below 90% before 13.5v provides any net charge to the battery. After that with some cycling 13.5 will hold the battery at no more than 80%.

So if 13.5 is recovering your batteries immediately following a charge cycle that suggests that your 100% is my 85%.

I'm sure we could look up how much energy gets put into a battery at 13.5v. That might be a calibration point.

 

[Jeff F]

One more anecdote that's closer to home.

When I installed Lithium 3.5 years ago I deliberately wanted to rely on solar as much as possible. I was hanging out here and paying lots of attention to your thoughts and approach.

My takeaway was that hitting a conservative target voltage like 13.8 and dropping immediately into float might be a good practice, and that's essentially what I tried to do with my Balmar regulator, with a low float value.

I mentioned earlier that my current arrangement charges to 90% SoC. I'll now qualify that a bit. I should have said max 90%. If the pack is at higher charge it will cut out at about 90%, but if starting from a lower charge it'll cut out well before that.

I've come to recognize that voltage can be easily dragged around and stretched with these batteries. Getting to a target value is easy, but unless you have other markers to indicate equilibrium - like current tapering under constant voltage - it's pretty meaningless.

I'm happy to be challenged on any of this. I got interested in lithium in cars and RC boats, and it's been years since I had any major curiosities or experiences there. These thoughts are based on playing and monitoring with my system. I'm ashore for the first time in a while and reflecting on what I've learned.

 

[DDW]

Twistedtree - why do you need another shunt for the Wakespeed? One shunt can serve many instruments.

I agree that the need to measure battery current is tied to LA, particularly AGM, and LFP has much less need to do so - though for diagnostics, still very useful. The problem I had with the Balmar regulator on the AGM bank was that it switched to float prematurely, regardless of settings. This added an hour or two to reach full charge, and full charge is necessary for AGMs if you want them to last. Also the Balmar erroneously switched out of float to absorb frequently. Lifeline specifies 0.5% C charge rate as full, on my 600 AH bank that is 3 amps. Even then theory that the Balmar could come close to that by guessing from field current, when the amp draw is varying from 15 to 100A while the engine is running is faulty, and in practice it did not work. I finally set the float to 0.1V below absorb, until I fitted the Wakespeed.

I'm skeptical that you have never had a thermal cutback on the Wakespeed alternator, given your setup. I'll bet if you logged the data you would see it. Unless you have the field maximum set to some low value. Logging the data, you will often be amazed at what you see.

 

[twistedtree]

Approach this as a calibration challenge. I'd posit that since you've never tried significantly higher thresholds (not just voltage, but termination as well) you don't really know where 100% is on your pack. That's fine.

I can tell you that when I charge my drop-in pack to the max recommended 14.6v and leave the rest to the charger defaults my SoC under use will drop to below 90% before 13.5v provides any net charge to the battery. After that with some cycling 13.5 will hold the battery at no more than 80%.

So if 13.5 is recovering your batteries immediately following a charge cycle that suggests that your 100% is my 85%.

I'm sure we could look up how much energy gets put into a battery at 13.5v. That might be a calibration point.

OK, I see what you are saying now. I agree and presume that different manufacturers set their 100% SOC level to different points. Mine happens to come from by BMS, and based on how the BMS is controlling DVCC, I can see what voltages they are charging too. And I suspect you are right that the differences we are seeing is just a result of the 100% SOC point being different.

Once mine hit the full charge voltage and the Wakespeed kicks into float, the alternators shut off and all power loads come from the battery while the voltage drops from the bulk to float voltage. I'm running from memory on these numbers, but the load is in the order of 100A. This lasts for no more than a minute or two. As the voltage reached the float voltage, the alternators ramp back up and I end up with a positive 10-20A charge rate at 13.5V. The charge rate remains positive like that until the batteries reach 100% SOC.

Looking at how many Ah are involved, let's say it takes a full 5 minutes from teh time the alternator shuts off and when it comes back on at the float voltage. At 100A draw, that's 8Ah draw out of the batteries. Then looking at what ends up being a slow charge to 100% at 13.5V, I would estimate it takes 2 hrs to get from 95% to 100%. At 20A that's 40Ah. 5% of my battery bank is 84Ah, so these numbers don't add up. It's probably because I'm not remembering the numbers correctly, and will be interested to monitor it more closely next time I leave an anchorage.

I also think part of what we might be seeing is the effect of charging to a voltage at different current rates. They don't get you to the same SOC. So charging to 14V at .5C might get you to 90%, where charging to 14V at .1C will get you higher. Another way to look at it is that if you are only using the cut off voltage to charge to 100%, you need a higher cutoff voltage the higher the charge current. With just alternators I'm charging at about 0.16C

 

[twistedtree]

Twistedtree - why do you need another shunt for the Wakespeed? One shunt can serve many instruments.

I agree that the need to measure battery current is tied to LA, particularly AGM, and LFP has much less need to do so - though for diagnostics, still very useful. The problem I had with the Balmar regulator on the AGM bank was that it switched to float prematurely, regardless of settings. This added an hour or two to reach full charge, and full charge is necessary for AGMs if you want them to last. Also the Balmar erroneously switched out of float to absorb frequently. Lifeline specifies 0.5% C charge rate as full, on my 600 AH bank that is 3 amps. Even then theory that the Balmar could come close to that by guessing from field current, when the amp draw is varying from 15 to 100A while the engine is running is faulty, and in practice it did not work. I finally set the float to 0.1V below absorb, until I fitted the Wakespeed.

I'm skeptical that you have never had a thermal cutback on the Wakespeed alternator, given your setup. I'll bet if you logged the data you would see it. Unless you have the field maximum set to some low value. Logging the data, you will often be amazed at what you see.

My BMS is the source for battery current, not a separate shunt.

I'm pretty sure on the alternator temps. I haven't watched it 100% of the time, but it gets the hottest after leaving an anchorage when charging batteries at full output. After everything is heat soaked the Wakespeed is reporting about 80C at the rectifier and is set to throttle at 100C. Maretron is reporting ~300F on the stator. The alternators are among the few that are designed for continuous output.

 

[DDW]

What model alternator?

 

[SteveK]

The chart below shows my expereince with LFP. I have deliberately discharged to ~10% with 12.6v and watched the voltage & SOC along the way.

 

[Jeff F]

I also think part of what we might be seeing is the effect of charging to a voltage at different current rates. They don't get you to the same SOC. So charging to 14V at .5C might get you to 90%, where charging to 14V at .1C will get you higher. Another way to look at it is that if you are only using the cut off voltage to charge to 100%, you need a higher cutoff voltage the higher the charge current. With just alternators I'm charging at about 0.16C

Yes, I'd agree with that observation. That's why I think the absorb phase matters. The farther/faster you force a voltage change, the longer you have to hold it to make it stick.

 

[SteveK]

Yes, I'd agree with that observation. That's why I think the absorb phase matters. The farther/faster you force a voltage change, the longer you have to hold it to make it stick.

Absorb discussions with LFP suggested not needed, I disagree. Bulk charges to absorb and absord keeps current following into battery, cut it short and 100% SOC may not be achieved.

 

[Jeff F]

Once mine hit the full charge voltage and the Wakespeed kicks into float, the alternators shut off and all power loads come from the battery while the voltage drops from the bulk to float voltage. I'm running from memory on these numbers, but the load is in the order of 100A. This lasts for no more than a minute or two. As the voltage reached the float voltage, the alternators ramp back up and I end up with a positive 10-20A charge rate at 13.5V. The charge rate remains positive like that until the batteries reach 100% SOC.

I'll offer a prediction here. I think that each discharge cycle draws down the voltage a little bit. Bringing the battery back to 13.5 doesn't replace all the lost energy. My experience cycling at a fixed voltage is that SoC gradually falls.

Think of it this way. If you start out at full charge and hold at 13.5v with a trickle discharge the battery will stabilize at XX% SoC.

If you take a discharged battery and hold at 13.5v the battery will stabilize at a much lower SoC. Maybe if you leave them hooked up forever they approach the same state, but I'm not sure it'll ever happen.

 

[twistedtree]

What model alternator?

Delstar 180 (I think, again going from memory). 250A each at 24V, and I have two of them. With full field they put out about 275A initially, but once they warm up it drops to about 225A. I really like them.

 

[twistedtree]

Absorb discussions with LFP suggested not needed, I disagree. Bulk charges to absorb and absord keeps current following into battery, cut it short and 100% SOC may not be achieved.

I agree, but I don’t care if I give up a couple percent. In exchange you get simpler charging, lower chance of an unexpected disconnect because of cell imbalance, and maybe temp too. Plus likely longer battery life, but that’s unquantified.

 

[twistedtree]

Think of it this way. If you start out at full charge and hold at 13.5v with a trickle discharge the battery will stabilize at XX% SoC.

In practice I don’t see this happen. I may see a brief discharge current, then a charge current, etc. There is never an ongoing trickle discharge. The alternator covers the DC loads. I think the longest I have been underway like this is perhaps 36hrs, and SOC doesn’t budge. I think to stabilize at a lower SOC the voltage needs to be lower. I think more like 3.4 vpc.

 

[Jeff F]

In practice I don’t see this happen. I may see a brief discharge current, then a charge current, etc. There is never an ongoing trickle discharge.

My example may be a bit too contrived.

In your use case described above if you held that 100a load for an hour instead of a few minutes your SoC when the battery gets back up to 13.5 will be lower.

ETA: it occurs to me on rereading that maybe I'm not understanding your regulation. A smart regulator may try to cover a large share of the load, but that's by breaking the constant voltage rule. At least that's my simplistic view.

 

[Jeff F]

I agree, but I don’t care if I give up a couple percent. In exchange you get simpler charging, lower chance of an unexpected disconnect because of cell imbalance, and maybe temp too. Plus likely longer battery life, but that’s unquantified.

I buy this. Here are my disagreements, based on having used this approach with my alternator regulation.
1) the battery may drift out of balance over time. You and I agree that this is low risk, but the best defense is regular full charging.
2) You may give up a lot more than a few %, especially with a deeper charge cycle. That was the big unexpected takeaway for me.

 

[twistedtree]

My example may be a bit too contrived.

In your use case described above if you held that 100a load for an hour instead of a few minutes your SoC when the battery gets back up to 13.5 will be lower.

ETA: it occurs to me on rereading that maybe I'm not understanding your regulation. A smart regulator may try to cover a large share of the load, but that's by breaking the constant voltage rule. At least that's my simplistic view.

OK, that may be. I have not tried that.

 

[twistedtree]

I buy this. Here are my disagreements, based on having used this approach with my alternator regulation.
1) the battery may drift out of balance over time. You and I agree that this is low risk, but the best defense is regular full charging.
2) You may give up a lot more than a few %, especially with a deeper charge cycle. That was the big unexpected takeaway for me.

Re 1, I agree if balancers only run when at elevated voltage. Most do, but not all. The MG balancing works differently, but I think they are unusual in that respect.

Re 2, that may be. I haven’t tried it, and am not recalling any research that has quantified it.

 

[twistedtree]

This has been a good discussion. Now we just need to hear how Kevin has made out with his Zeus….

 

[Jeff F]

The chart below shows my expereince with LFP. I have deliberately discharged to ~10% with 12.6v and watched the voltage & SOC along the way.
View attachment 162314

Sure, if you discharge at a slow constant rate this holds true. But throw in a high discharge event and it goes out the window.

Try charting voltage vs SoC while charging. The difference might surprise you.

 

[SteveK]

Sure, if you discharge at a slow constant rate this holds true. But throw in a high discharge event and it goes out the window.

Try charting voltage vs SoC while charging. The difference might surprise you.

OK, Tell me how you would do that, step by step of what you mean.
Maybe show me your voltage v. SOC
I have only seen ~200A going in over x hours to replace depleted Ah and voltage was mostly around 13.2v. on the graph it would show as high as 14.4v. It would say IE: 3 hrs 15m to full charge and it was close enough for me. The charge gradually reduced. Then it would go to float 13.5v and charger would match loads under 40A and bats stay 100%.

 

[Bmarler]

Sure, if you discharge at a slow constant rate this holds true. But throw in a high discharge event and it goes out the window.

Try charting voltage vs SoC while charging. The difference might surprise you.

Is it really that surprising? Don’t they have a high acceptance rate, shown by a high current draw and voltage slow climbing till they reach some point where the voltage climbs to the bulk setpoint and current draw slows? Would that point be about an 80% charge?
I’m not being snarky, I really want to know.

 

[Jeff F]

Is it really that surprising? Don’t they have a high acceptance rate, shown by a high current draw and voltage slow climbing till they reach some point where the voltage climbs to the bulk setpoint and current draw slows? Would that point be about an 80% charge?
I’m not being snarky, I really want to know.

No snark taken. I'm throwing it out to try to show where voltages can become seriously disconnected from SoC. If you start cycling to any extent that disconnect can be persistent.

Once untethered it's only in the top or bottom 5% range where you can establish a reliable connection between voltage and SoC. It's easy to do balancing there too.

That's a key characteristic with Lithium. 'Resting voltage' has some meaning with LA. I think with Lithium it's a misnomer.

To your question, the higher the setpoint voltage, the more reliably you can stop charging at a known SoC. That's a function of the chemistry. It's the 'current drain slows' that's problematic.

 

[Jeff F]

... Then it would go to float 13.5v and charger would match loads under 40A and bats stay 100%.

I'm not sure what we're debating here. If you're trying to dispute my claim that batteries won't stay at 100% float then I'm going to claim your 100% calibration is incorrect. See above conversation.

There are a few moving pieces here. They can't be discussed in isolation.

 

[ksanders]

This has been a good discussion. Now we just need to hear how Kevin has made out with his Zeus….

That will be a month or so as my boat is on the hard getting a bit of work done in Ensenada. I am looking at launching the 2nd week of March.

Also part of this is I want to connect the BMV-712 Victron shunt which is configured as a alternator monitor to the cerbo and see how the display reacts. Plus with the Zeus regulator they say that will talk to the Cerbo and I want to see how that functionality works.

 

[Barking Sands]

I could turn this around - if you start with a dead battery and charge with 13.5v until current reaches zero, what will the SoC be? It's not going to be 100% of the possible maximum charge.

Just some thinking out loud. No guarantee that I am right about any of the following:

I am thinking maybe too much attention is paid to SOC? I dont really know of any batteries that have SOC tied to anything directly except a reset to 100% at a known position that is semi-arbitrarily set by drop in manufacturers or user set with things like the Victron shunt, followed by a counting of current in/out.. "Charged detection criteria" is set in the Victron shunt in three places that will together reset SOC to 100%. If I remember correctly...its Charged voltage, tail current and charged detection time. Typically, Victron recommends a charged voltage of .2 volts less than absorption. Tail current is a percent of total capacity and detection time is how long the two other values are seen. Once that happens then it just resets SOC to 100%. As far as I can tell SOC in all LFP batteries was added as a convenience item to give users a half decent fuel gauge since the flat voltage no longer allowed good capacity tracking. In drop in batteries those values are set by the manufacturer and not settable of course. In addition things like "current detection threshold" of the Victron shunt or the in the case of drop ins...the internal shunt have varying levels of accuracy. Its well know the Epoch V1 had a current detection threshold of 1.3 amps. Anything less was invisible to calculate SOC. The Victron shunt is settable but comes preset to .1 amps. And they warn setting it too low can induce/pick up on noise in the system to make amp measuring inaccurate if set too low. So .1 is probably good. The current detection thresholds conspire to add drift into SOC calculation and tracking for very low draws/charges, or every time the current direction is reversed if that reversal isn't symmetrical in time spent under the thresholds at low currents in each direction. I have a theory that this is why SOC on solar tends to drift so much more than something like inverter/charger charging. But solar can also spend a very long time in a midrange SOC without ever getting to the SOC reset criteria. A few weeks on solar without ever reaching SOC reset and the drift accumulated is likely significant. Floating for extended periods as well.

Jeff, in your quote above you say charging to 13.5 will not result in 100% SOC. But what if that is only due to previously induced and accumulated drift in SOC accuracy and the fact that the system hasn't achieved the SOC reset criteria? Since SOC seems to be such a poor indicator of actual capacity it would seem that the only way to determine the state of the battery after charging and absorbing at 13.5 volts is by experiment by doing an actual capacity test. One of the best tests I have ever seen was Ben Steins tests in this article.

Charging LiFePO4, what's the impact of lower voltages?

What voltage should I charge my LiFePO4 batteries? That seems like a simple question likely to have a single, direct answer. But, the actual answers are often unclear. Many LiFePO4 battery manufacturers recommend 14.6 volt absorption. But, that singular recommendation doesn't account for...

panbo.com

He charges and cap tests a 100AH battery at voltages from 13.2 to 14.6. It must have taken quite some time to compile. Only at 13.4 did the battery not quite achieve full rated capacity on discharge tests. 13.5, when full absorbed essentially matched all voltage above it for capacity. But charge speed took a big hit. In actuality 13.4 did make rated capacity but all higher voltages added another 3ah or so. You can also use Bens charts to help inform for absorption time.

I don't put too much stock in SOC unless I know I have recently hit the SOC reset point AND haven't spent extended time near very low currents in and out. Boat systems that float for long periods accumulate drift in SOC. Solar systems that spend many days in a mid level SOC with lots of in/out reversals at very low currents and dont make it to SOC reset for days weeks or even months will be wildly inaccurate. But charge up a golf cart to 14.6 which resets SOC, followed by a hard drive where amp draw is hefty and constant with no reversals and SOC will be fairly accurate over the full discharge. When I had the V1s in the boat I would float for weeks at the dock. SOC would drift 4-7% from the Victron shunt and the Victron shunt was guaranteed to be less than perfect as well (but much better than the EpochV1). I could care less about the SOC because as long as I hit my voltage and absorption marks I knew the battery had 100% capacity or very very close. Hitting those marks also were guaranteed to reset the Victron SOC but not the Epoch SOC. So there was that too. So If I wanted to align them I would just ensure that on the next charge cycle I hit all the marks of the various SOC tracking meters and they all reset to 100%. Then its just a slow slide of SOC drift away from accuracy over time.

So you dont need to charge to 100% SOC. You need regular visits back to SOC reset criteria. To further illustrate, I have seen the opposite effect where 100% SOC was reached too early at too low of a voltage to be considered full capacity. Obviously, the SOC meter wont go above 100% so it just continues to charge at a decent amp rate for long periods sitting at 100% until the programmed charge cycle is met. Again, soc was just along for the ride.

In practice I don’t see this happen. I may see a brief discharge current, then a charge current, etc. There is never an ongoing trickle discharge. The alternator covers the DC loads. I think the longest I have been underway like this is perhaps 36hrs, and SOC doesn’t budge. I think to stabilize at a lower SOC the voltage needs to be lower. I think more like 3.4 vpc.

I agree. Its still all about the voltage from what I can gather. And 3.4 vpc should give full capacity as measured by a proper capacity test. Especially for the longer runs. I am sure battery charge current had long dropped to 0. Andy at Off Grid Garage on Youtube did many cell level tests over the years similar to Ben Steins tests of a complete battery and came to the same conclusions regarding voltage, absorption time VS measured capacity. The only difference between the cell level testing and the full battery testing was the addition of an SOC meter, that in reality is a marginal tool. I am sure your all Victron system is very accurate for SOC. But I also believe it will rebulk every 7 days (or maybe s BMS managed for rebulk?) which will reset the SOC at regular intervals.

On of the biggest tip offs that SOC (especially in drop in batteries with Bluetooth) is to be viewed carefully and skeptically is dealing with many golf cart users. Many new golf cart people with their new lithium drop in batteries would charge up the packs with the simple Cc/Cv charger to max voltage of 14.4 to 14.6 volts. This would always reset SOC to 100%. They would go on the long drive and come back with SOC at 20%, but they would charge again and manually stop the charge at 80% because thats what they read they should do. After doing so 6 or 7 times they would head out with 50% remaining only to have the SOC drop to 0 all of a sudden, the cart dies a mile from home. Many BMS have a low voltage SOC reset as well. But its just prior to discharge mosfet disconnect....lol.