Alternators - leave them alone and forget about them

[Jeff F]

To me, the insight into BMS behavior, etc. is not just about what happens after a disconnect, but knowing you're at risk for one before it happens. Knowing that could prevent an unexpected loss of house power due to the overload cascade TT mentioned if you're under heavy load when part of the bank disconnects, causing an overload on the other BMSes.

Catch up, man. Go back and start from the beginning.

 

[Jeff F]

I would really like to line up two extreme cases - TT's and mine. Make sure they're well understood by all, then contrast and compare. The actual implementation will vary. I'm using some vaporware in my example.

Let's lay down some basic requirements:

1) fully functional ATC/ATD at pack level. 2) Cell monitoring is not required beyond operational needs. User monitoring is optional.
3) long term stability and safety is unquestionable

I hope that gets us going in the right direction.

 

[Barking Sands]

To me, the insight into BMS behavior, etc. is not just about what happens after a disconnect, but knowing you're at risk for one before it happens. Knowing that could prevent an unexpected loss of house power due to the overload cascade TT mentioned if you're under heavy load when part of the bank disconnects, causing an overload on the other BMSes.

IMO there are very few scenarios that are going to let you know before they happen.
-A failing cell or cells with slowly dropping voltage
- temperature issue, almost certainly high temp that's rising slow.

Most other types of failures in electrical equipment IMO tend to be fast acting. Some internal, some external. I think someone here even alluded to the fact the requirement to notify via alarm of "impending failure" was dropped from the ABYC. Being notified of all impending failures is really an intractable problem.

Overlay the impending failure with a single large battery bank with a single connected and integrated BMS. The very expensive kind. What are you going to do? You get an alarm of impending failure and you have say 20 minutes. As described in some systems here, you then have 20 minutes to do whatever you can think to do and then the house bank and maybe even the alternator are locked out until repairs are made. That is better than nothing and gives time to drop anchor...maybe. You could have 2 of these system side by side for redundancy, that would help. Big money.

But compare that to a modular/redundant design making use of good quality drop ins. Your total amp requirement is say 300 amps max. You buy 5 good quality drop ins of the type I posted above. That is 600 continuous AMPS available and 500 AH available. You could loose 2 batteries from malfunction and still not have a cascading event. Dont forget if you have a scenario where the amp draw far exceeds the 300 amp design requirement it would pop the required fuse or fuses regardless of the system type. So really a cascading event is highly unlikely in a properly designed system.

If you have 2 batts with 50 amp BMS's and routinely power 80-90 amps and one battery fails and locks out that would be a cascade to shut down the other battery and be without power.

 

[Jeff F]

And B,S. takes the middle ground ..

My solution is 10 x 100ah x 50a under a MBMS. No cell level monitoring.

MBMS will provide following functions
- ATC/ATD and/or warning thresholds configurable by user
- recognize when a battery goes offline, even briefly
- provide monitoring of battery voltages, and perform routine balancing of pack.
-
I'm thinking as I type. Let's say also that it provides individual battery disconnect and easy cabling connections for each battery. We're only talking 50a each. Aw heck, let's also throw in MBMS temp sensor with provision for external next to batteries. At 50a let's include some basic amperage per battery as well.

Let's put battery cost at $350/ea. I haven't researched. Price is key.

Edit to add: too high. My 300ah 200a are $1050. So let's say $300, for the sake of argument.

 

[Barking Sands]

And B,S. takes the middle ground ..

Thats the way its shaking out. 3 levels from 3 perspectives. I do appreciate all the input.

BTW...take a look at the battery I posted representing the middle ground. In the page for Epoch Batteries they link 3 videos near the bottom from Will Prowse and others. Its quite an amazing battery for the money. Only the top video shows the remote monitor. That monitor could be placed in plain view and it shows status and sounds alarms for each battery. Each batter has a monitor. Let me know what you think.

https://www.epochbatteries.com/?rfsn=7026032.670492

 

[Jeff F]

If you like it I'm happy

 

[DDW]

Rod was describing the cheapest of the cheap direct from China from several years ago. It might actually be hard to find a battery like that now unless you go searching for it...lol.

In the last year, I have purchased some LFP batteries and (since they failed in use) tested their capabilities. They came no where near the advertised spec. They weren't bottom fished either. So yes, you can find bad batteries. This is one serious problem with sourced in China, no-name, house branded batteries (or any product) purchased from unreliable suppliers. You don't know what's in there unless you take the top off. And you don't know that the one Will got was the same as the one you got. I've looked at a shelf full of batteries in the store, all with the same label and part number, but which were clearly from different manufacturers.

There are some higher quality drop ins that you can take the top off, and can service the cells if needed. The Epoch batteries are an example. The cheaper ones, you pretty much destroy the case taking them apart.

 

[twistedtree]

Rod was describing the cheapest of the cheap direct from China from several years ago. It might actually be hard to find a battery like that now unless you go searching for it...lol.
But...I am not sure what everyone has in their own mind for the "cheap" drop ins. Some might be seeking out that $199 Lifepo4 "deal".
I am hoping most are thinking of the more typical $300-400 range 12 volt 100AH battery from Amazon such as Ampere Time or Chins for the low end.
You can also get their "smart" batteries for about a 20% premium.
Any of these drop ins for a boat house bank IMO should have an on/off switch and bluetooth monitoring at the cell level along with warning. Here is the battery I just purchased for my Golf Cart:

https://www.epochbatteries.com/?rfsn=7026032.670492

But they also have:
12 volt 100AH
24 volt 100AH
36 volt 100AH
48 volt 100AH.

All have:
Bluetooth that can see all cells
many warnings
self heating for cold weather charging
IP67 rated waterproof case with mounting bushings
many protections (high/low temp, voltage, amperage etc)
11 year warranty from a large company (engineered in the US)
Data sheets for all testing and specs
2 CAN ports
On/Off switch on each unit
A remote dash mounted monitor that sounds all the warnings noted in bluetooth. This is connected to a CAN BUS plug
many certifications such as UL, CE. FCC and SAE
removable top, seems to be semi serviceable

Three videos from Will Prowse, Lithium Solar and some other guy that have rave reviews about the internal build quality.

And this battery cost $599 currently. That seems impressive. But I will test it when I get it in my hands and see how that translates into the discussion we have been having. I asked them about the CAN plug output that the external monitor plugs into and whether or not it could interface with Victron stuff. He said they are looking into that but that they would very much like to make it communicate with Victron stuff.
He also stated they plan to come out with 270Ah and 540AH versions.

I have heard this is where "drop-ins" are going, and I think it's in the right direction.

 

[twistedtree]

And B,S. takes the middle ground ..

My solution is 10 x 100ah x 50a under a MBMS. No cell level monitoring.

MBMS will provide following functions
- ATC/ATD and/or warning thresholds configurable by user
- recognize when a battery goes offline, even briefly
- provide monitoring of battery voltages, and perform routine balancing of pack.
-
I'm thinking as I type. Let's say also that it provides individual battery disconnect and easy cabling connections for each battery. We're only talking 50a each. Aw heck, let's also throw in MBMS temp sensor with provision for external next to batteries. At 50a let's include some basic amperage per battery as well.

Let's put battery cost at $350/ea. I haven't researched. Price is key.

Edit to add: too high. My 300ah 200a are $1050. So let's say $300, for the sake of argument.

I think you plan to wire all the batteries in parallel, right? That will make the battery voltage for each battery the same, so no way to detect cell voltage variations, or even battery variations.


To really tell anything, you would need to have a current sensor for each battery. No current flow in a battery would tell you that it has disconnected. Assuming it remains disconnected, then you replace it. If it's transient, then I guess you see if it repeats and if it does, replace it.


You might be able to glean other insight based on current variance from battery to battery, but it will be tricky since there will always be some variance based on cell and connection resistance variation. So the trick would be distinguishing normal from abnormal.


I'm not sure what balancing you will be able to do, since that happens naturally for batteries wired in parallel. And of course you can't balance cells.


And what will ATC and ATD be based on? Bank voltage is already available to chargers and used to control charging, so I'm not sure what additional insight you can bring to teh table with ATC/ATD from such a MBMS


I think if you are using 12V batteries to make 24V or 48V banks, then there is some value in monitoring per-battery voltage. This is more generically referred to as mid point measuring, and is a form of poor-man's cell monitoring. If the two halves of the battery measure different voltages, then you know you have an imbalance. It's not perfect because you could still have an imbalances within a battery, but nominal voltage overall. But it gives you a shot at detecting imbalance. But it begs the question of what you do about it. You would add or subtract charge to whole batteries, but that doesn't address individual cells that are high or low.


Regardless, I think your commodity approach to batteries is interesting. I think it's value depends greatly on the spread in cost between low-function and higher-function batteries, and how closely you can replace the capabilities of a higher-function battery.

 

[twistedtree]

IMO there are very few scenarios that are going to let you know before they happen.
-A failing cell or cells with slowly dropping voltage
- temperature issue, almost certainly high temp that's rising slow.

Most other types of failures in electrical equipment IMO tend to be fast acting. Some internal, some external. I think someone here even alluded to the fact the requirement to notify via alarm of "impending failure" was dropped from the ABYC. Being notified of all impending failures is really an intractable problem.

Overlay the impending failure with a single large battery bank with a single connected and integrated BMS. The very expensive kind. What are you going to do? You get an alarm of impending failure and you have say 20 minutes. As described in some systems here, you then have 20 minutes to do whatever you can think to do and then the house bank and maybe even the alternator are locked out until repairs are made. That is better than nothing and gives time to drop anchor...maybe. You could have 2 of these system side by side for redundancy, that would help. Big money.

But compare that to a modular/redundant design making use of good quality drop ins. Your total amp requirement is say 300 amps max. You buy 5 good quality drop ins of the type I posted above. That is 600 continuous AMPS available and 500 AH available. You could loose 2 batteries from malfunction and still not have a cascading event. Dont forget if you have a scenario where the amp draw far exceeds the 300 amp design requirement it would pop the required fuse or fuses regardless of the system type. So really a cascading event is highly unlikely in a properly designed system.

If you have 2 batts with 50 amp BMS's and routinely power 80-90 amps and one battery fails and locks out that would be a cascade to shut down the other battery and be without power.

All good points, but I want to clarify what's intended by the various alarming that we are talking about. It's alarming to indicate the battery is being driven outside it's safe operating envelope ("SOE" in ABYC lingo). In most cases, this is a direct consequence of charging outside of allowed ranges such that current limits, voltage limits, or temp limits are exceeded. The other is a consequence of excessive discharge that can also exceed current or voltage limits. The alarms are NOT predictions of electronics or cell failures, although such failures might result from exceeding the SOE. At least with ABYC, the limits are about SAFETY. They are NOT about asset protection, though again, keeping the battery away from unsafe conditions is likely to also protect it from damage.

 

[twistedtree]

Can you run through the recovery and repair of a single cell in a purpose built pack with single integrated BMS? Maybe also what a cell failure looks like in practice? Also, can you point to an example of a battery system that you are likely thinking of to contrast? Maybe even a picture. I am sure you have made a post before. Maybe just point me in the right direction so I can take a gander. Much appreciated.

I get the feeling we are still adding ALL the details in a pro/con list still. I think that list is incomplete as of yet. I also get the feeling there will be more than one way to do these things in a perfectly acceptable manner. But IMo we still need to add details to the discussion.

I think the most likely unexpected shutdown cause for a BMS is a cell that is out of balance WRT to other cells. The battery voltage will look fine and charging or discharging will be underway, currents are comfortably in range, but the BMS disconnects because that one cell is too high or too low. This WILL eventually happen if 1) there is no balancer, 2) the balancer is inadequate as they appear to be in some drop-ins, or 3) the battery isn't charged in such a way that allows the balancer to run enough. Also note that even with balanced cells, an improperly controlled charger that tries to overcharge the batteries will likely trigger a BMS disconnect. But I would consider that a fault condition, not an operational disconnect.



The next most likely, I believe, is an over-current disconnect, and this is much more likely with a FET-based (solid state vs contactor) BMS disconnect switch. FET disconnects are more limited in current capacity than a contactor, and cheaper FET disconnects have lower capacity. That's why you see some 100Ah batteries with a 50A rating and others with a 100A rating. FET switches are also subject to getting fried by large current surges (thrusters, engine starters, windlasses) that smoke the FETs before the BMS can disconnect. If over-currents like these occur, it's really because of a poorly designed/sized system. This is why most FET-based batteries prohibit use with such high surge current devices.



Next would be high or low temp disconnects. This obviously relates to ambient temp, but high charge and discharge currents will drive up cell temps.


These are the operational causes of disconnects, and should NEVER happen in a properly working system.


As for diagnostics and repair of a failed cell, I'm not aware of any manufacturer that allows field replacement of a cell. Their BMS can typically show a failed cell, but field replacement is of the whole battery, not the cell. The only situation where a cell would be replaced would be with a discrete system. At this point I don't think very many people are going that route anymore, but some still do, and quality battery systems can be built up this way. I built my home battery system this way and it is running great, now 4 years in. Cell replacement would depend greatly on the physical build, but presumably would be possible.


There are a few examples of what I would consider to be full-function battery systems, and I'll describe the one I have on my boat. It's built by MG Energy, and consisted of batteries with built-in cell sensing and balancing, coupled with an external BMS and contactor. Cat5 cables connect the batteries and BMS for communications and control, and the battery DC cables connect back to the BMS where they share a single contactor. The BMS is rated for 1000A.



The BMS provides two key signals, ATC and ATD which are used to enable/disable chargers and loads. All my chargers are programmed to charge within the allowed ranges for the batteries, so ATC always says charging is allowed. That said, ATC is wired to my shore chargers, inverters, and alternators and will turn them off if for any reason ATC shuts off. Referring to the above discussion, if cells have become imbalanced, battery bank voltage can appear OK and chargers will keep running, even though a single cell is heading out of range. This is where ATC shuts off charging, and averts what would otherwise be a BMS shutdown and potential alternator surge event.


ATC also protects against over temp and other events that are otherwise undetectable by chargers, and would lead to a BMS disconnect.


ATD controls the inverters and will shut them down if batteries become critically low. But my other DC loads will not shut off. I use ATD as an alarm, but specifically do not want other loads to shut down. I would rather have power as long as possible to give time to get an alternate power source going, etc. I also have generator autostart that kicks in well before ATD triggers.



As a result of all this, if a BMS disconnect happens, something is pretty broken, either on the charging side, or in the BMS itself or a cell.

 

[ronobrien]

I don't feel the need to have high capacity charging from my alternators, but some is necessary. It helps power the windlass (run from the house bank) and my electronics are all powered from the house bank. So with no alternator input, I'd just be drawing the batteries down if I run at night when there's no solar input.

The other time I appreciate alternator charging is if we've had cloudy weather and are down on power, but going to move the boat. The extra fuel burn from higher engine load for more alternator demand is less than I'd burn by firing up the generator for a couple hours to throw a similar amount of power into the batteries.

Main diesel engines don't like to be run with a light load such as charging only. They run at reduced cylinder pressures which does not properly seat the rings to the cylinder walls. Over extended periods this can cause reduced compression and a cascading set of events from there. This is old school knowledge, the newer diesels may be different and I am not up to date, just something to keep in mind when designing for regular use.

 

[rslifkin]

Main diesel engines don't like to be run with a light load such as charging only. They run at reduced cylinder pressures which does not properly seat the rings to the cylinder walls. Over extended periods this can cause reduced compression and a cascading set of events from there. This is old school knowledge, the newer diesels may be different and I am not up to date, just something to keep in mind when designing for regular use.

Agreed, I wouldn't want to fire up the mains just to charge batteries. I don't even particularly like firing up the generator just for charging. I'd rather have enough solar to handle most charging needs, enough battery to last through a couple of cloudy days, and then be able to make up the rest with incidental charging when the mains or generator are already running for another purpose.

 

[Barking Sands]

Thanks for the reply TT. Im going to have to digest what has been covered so far. My brain is nearly full. I appreciate everyones input on these discussions.

 

[DDW]

I think if you are using 12V batteries to make 24V or 48V banks, then there is some value in monitoring per-battery voltage. This is more generically referred to as mid point measuring, and is a form of poor-man's cell monitoring. If the two halves of the battery measure different voltages, then you know you have an imbalance. It's not perfect because you could still have an imbalances within a battery, but nominal voltage overall. But it gives you a shot at detecting imbalance. But it begs the question of what you do about it. You would add or subtract charge to whole batteries, but that doesn't address individual cells that are high or low.

You can buy mid-point balancers, which sense and balance between two (or more) 12V batteries in series. If the drop ins have adequate internal balancing, then everything should be kept in balance. Of course, many of the balancing schemes are top-of-charge only, so if you habitually operate at PSC, the balancer may not have the capacity to accommodate the result when you do eventually charge to 100%, then you might get a disconnect even though you have always stayed within the SOE. Again, this is weakness of many drop-ins, they are poorly documented and you have little idea of what the BMS does. The Epoch, and some of the other higher end drop ins have a Bluetooth connected phone app which gives you the individual cell voltages, so with diligent monitoring you could manage it.

 

[Jeff F]

Main diesel engines don't like to be run with a light load such as charging only. They run at reduced cylinder pressures which does not properly seat the rings to the cylinder walls. Over extended periods this can cause reduced compression and a cascading set of events from there. This is old school knowledge, the newer diesels may be different and I am not up to date, just something to keep in mind when designing for regular use.

Yep. I thought about that. I was putting a couple of HP into the alternator, so it's not no load. But agree it's not a good long term habit.

 

[Jeff F]

I'm not sure what balancing you will be able to do, since that happens naturally for batteries wired in parallel. And of course you can't balance cells.

And what will ATC and ATD be based on? Bank voltage is already available to chargers and used to control charging, so I'm not sure what additional insight you can bring to teh table with ATC/ATD from such a MBMS

Sorry I brought up balancing. Not for parallel. I was thinking about generic MBMS capabilities, which could include support for series arrangement. I was throwing out ideas as I had some RW obligations.

My MBMS would issue ATC/ATD based on following:
a) pack current or voltage threshold exceeded
b) failure of x batteries in the pack, as indicated by battery BMS activation.
c) ambient battery compartment temps

If in cold climates a heater in the battery compartment seems to me to be just as effective as individual battery heaters. The MBMS could conceivably manage heater control.

The MBMS would alert operator when one battery shut off. In a perfect world a transient shut off would be recognised as such, and root cause could be examined. Or as I suggested earlier, the battery gets swapped immediately.

What have I missed?

My 50a BMS example probably doesn't make real world sense, although I could change my example to 10 x 50ah 50a batteries.

 

[Jeff F]

The MBMS could also be used with smart drop ins. If it were an off-the-shelf solution it could open more possibilities for anyone building a bank of drop ins.

 

[Jeff F]

I would point out that in a drop in cell voltages may be interesting, but if they go out of whack it's likely an indication that the battery is nearing end of life. There's not a lot you can actually do to remediate the issue.

 

[Simi 60]

So if one of your batteries does a disconnect, you toss it?

It's a worry isn't it

 

[twistedtree]

I would point out that in a drop in cell voltages may be interesting, but if they go out of whack it's likely an indication that the battery is nearing end of life. There's not a lot you can actually do to remediate the issue.

Or that it just needs balancing. Otherwise these batteries won’t last very long.

 

[twistedtree]

BTW, a system like I described in 161 isn’t really more expensive than drop ins. Mine was about $7-$8 per Ah @12V, so equivalent to $700-$800 for a 100Ah 12V drop in. From what I’m seeing, drop ins in that capacity range from $500 for a cheapo, to $1000 for a name brand. So this notion that a more functional system is much more expensive isn’t really accurate. I actually think that once you add DC to DC converters, alternator protectors, etc you may end up with a more expensive system, and one that is actually less “drop in” than the more functional variants.

 

[Jeff F]

Of course, many of the balancing schemes are top-of-charge only, so if you habitually operate at PSC, the balancer may not have the capacity to accommodate the result when you do eventually charge to 100%, then you might get a disconnect even though you have always stayed within the SOE.

Right. I think most people do charge to full capacity regularly, so hopefully internal balancing works as designed.

In a parallel bank having an individual battery cut out in boundary cases - very low or very high SoC - may not be a problem as much as a cue that the battery is out of balance. Maybe you try to fix by cycling the battery a few times on the bench.

 

[Jeff F]

BTW, a system like I described in 161 isn’t really more expensive than drop ins. Mine was about $7-$8 per Ah @12V, so equivalent to $700-$800 for a 100Ah 12V drop in. From what I’m seeing, drop ins in that capacity range from $500 for a cheapo, to $1000 for a name brand. So this notion that a more functional system is much more expensive isn’t really accurate. I actually think that once you add DC to DC converters, alternator protectors, etc you may end up with a more expensive system, and one that is actually less “drop in” than the more functional variants.

I paid $3.50 per AH. Ampere Time. That leaves a lot of money for control/safety systems.

 

[Jeff F]

I'm going to change MBMS to BBMS. What I'm really describing is a bank BMS that allows you to easily and effectively make use of a variety of drop-in solutions, each having their own BMS.

Edit to add: the capabilities and features of each battery become much less interesting then.

 

[Jeff F]

My 50a BMS example probably doesn't make real world sense, although I could change my example to 10 x 50ah 50a batteries.

Just did a quick check and they're running at about $70/each. Probably $50 RW by the pallett.

Any failure swap out. Hobbyists will happily take rejects, and may even pay for them.

Edit to add: if you (stay well within BBMS capabilities or set conservative BBMS limits) and cycle the packs regularly failure should be uncommon once you've shaken the initial install out.

 

[Jeff F]

So couldn't I build an ABYC compliant installation without having cell monitoring? I should be able to. All I need is a fully-formed BBMS.

 

[Simi 60]

We paid less than $2 usd/ 12v ah

Matched and batched EVE 280ah 3.5v cells X 24 (8 makes a 24v @ 280ah batt)
A 200amp 24v JBD BMS and a 200 amp MRBF for each

Made 3 x totally independent batteries and, the boat will run on one - for the first few days we did just that as proof of concept
$3650 USD and that included delivery to the door China to Oz

Some assembly required

 

[Jeff F]

Made 3 x totally independent batteries and, the boat will run on one - for the first few days we did just that as proof of concept
$3650 USD and that included delivery to the door China to Oz

Some assembly required

So each battery has its own BMS?

 

[Simi 60]

So each battery has its own BMS?

Yes
And it's own MRBF