24v alternator protection using Alpha Pro regulator and Cerbo GX when charging LifePo4

[Vonasi]

I'm planning the electrical system for a narrowboat that I will start the build of later this year. I plan to have a 24v LifePo4 domestic battery bank built from Eve cells (either 8x280Ah or 16x280Ah 2P8S - yet to be decided) with a JK BMS and I would be interested on any thoughts on my possible system to charge these with an alternator from those more experienced in these set ups.

I plan to add a Mastervolt Alpha Pro III regulator to a 24v 100A alternator to temperature protect the alternator and to provide a 'small engine' mode for use at tick over speeds. However this does not protect the alternator from possible BMS charging disconnects that will blow the alternators diodes. I will however have a Victron Cerbo GX onboard and this has a relay output for starting a generator. The start and stop voltages can be adjusted on this so my thought was to use this to turn on and off the alternator regulator (perhaps via a solid state relay). So if the pack voltage gets to say 28.0 volts (3.50v per cell) then the Cerbo GX will turn off the regulator. I can then set a lower level for voltage to drop to to turn alternator charging back on. As long as the Cerbo GX's turn off voltage is well below the BMS maximum stop charging voltage the alternator diodes should be protected from any load dumps. I will also have a large solar array so I don't really need the alternator to be charging the LifePo4 to fill the last few % so these Cerbo settings could possibly be even a little more conservative.

Obviously there is an issue if the cells go well out of balance and one cell hits the 3.6v BMS stop charging voltage before the whole pack reaches 28.0v . The JK BMS has a powerful balancer built in so with well matched cells this shouldn't happen however in the event it does I plan to also have a Sterling alternator protection device (APD24) attached to the alternator. Sterling tell me these should not be used for protecting an alternator on an every day every charge cycle basis but are fine for occasional protection.

My engine starter battery will be 12v lead acid so I could simply charge that with a 12v alternator with smart regulator and then use B2B to charge the 24v domestic bank but this seems inefficient and has limited output and is also rather expensive compared to just using the Cerbo GX that I already have.

Yes I could buy a different BMS that has a relay output that could be used to turn off the alternator regulator but they all seem to a lot more expensive than the JK BMS.

Your thoughts would be appreciated.

 

[Vonasi]

Ok - my first post in these forums. 24 hours 30 views and not one answer.

Am I asking something very out of the ordinary? Am I asking in the right place? Have I worded my post so that it is difficult to understand? Or am I just trying to re-invent the wheel and no one want's to be the one to tell me why I shouldn't?

 

[svsagres]

Ok - my first post in these forums. 24 hours 30 views and not one answer.

Am I asking something very out of the ordinary? Am I asking in the right place? Have I worded my post so that it is difficult to understand? Or am I just trying to re-invent the wheel and no one want's to be the one to tell me why I shouldn't?

Too be honest, It's more that this is the first I've heard of this particular regulator. I've purchased a Wakespeed for my boat, and then there's the old standby by Balmar.

I like the WS500 because it's got the small engine/low RPM modes, integrates with the BMS and what not via CAN bus (so its output is controlled by the BMS), and also integrates with the rest of the victron and NMEA-2000 gear on the boat.

Given the flat charge curve of Lithium batteries, basing everything on voltage doesn't seem, to me, to be a great way to do things. Current based is better, but actually relying on signals from your BMS is the best way to go.

That's my $0.02

 

[Vonasi]

Thanks for your answer.

the Mastervolt Alpha Pro III also has a small engine mode but I don't believe that it has CAN Bus ability. I think the JK BMS might have but I'd need to double check the spec because some do and some don't.

I'm not a fan of Balmar and have been told of a lot of failures by someone in the industry.

It seems that I may have to rethink my BMS options and/or my regulator options as it makes sense what you say regarding not basing control on voltage with LifePo4. However I still think the system I described would be perfectly capable of doing the bulk of the charging via the alternator if a conservative Cerbo GX cut off voltage setting is used and then let the solar do the final top up in the last part of the curve without any fear of overcharging whether charging happens or not would now be down to the BMS only.

Surely even with a CAN bus controlled regulator there is the possibility that with a badly out of balance set of cells that the BMS would be switching alternator charging on and off based on just one cell continuously hitting the upper voltage before the others are anywhere near.

 

[svsagres]

Surely even with a CAN bus controlled regulator there is the possibility that with a badly out of balance set of cells that the BMS would be switching alternator charging on and off based on just one cell continuously hitting the upper voltage before the others are anywhere near.

In theory, yes, but the system should throw alarms before that happens. Additionally, the Wakespeed can be configured to go to a specific voltage on loss of communications. Additionally, if the REC I’m using detects a situation where a cell is out of balance, it will signal to the system to drop charging current to something within its balancing capabilities, so about 2A. Wakespeed will receive this, and ensure that no more than 2A is pushed into the battery.

 

[Vonasi]

That's interesting. The REC BMS has been recommended to me before but the price seemed a little eye watering compared to the JK BMS. Perhaps it has some features that make it worth the extra.

Perhaps a REC and a Wakespeed is something I should be looking into again.

 

[Vonasi]

I just had a look back at the REC and now remember some of my reasons for diregarding it.

It only has passive balancing on the version needed for 24v systems and although I'm sure this works fine it seems very innefficient compared to active balancing.

Also the communication is a bit clunky compared to others. Having to buy additional software and a cable to plug in a PC seems rather backward in this modern world of blutooth apps.

Plus there does not seem to be a UK distributor shown on their site. I'm sure there was one before. Perhaps this is another benefit of Brexit that they never told us about?

 

[RV10flyer]

I use a 50A 24V (28V) aircraft alternator, Transpo VR2400, 10000 ohm potentiometer to control field current/output to whatever I want. I monitor voltage, current, alternator temperatures.

 

[Vonasi]

I use a 50A 24V (28V) aircraft alternator, Transpo VR2400, 10000 ohm potentiometer to control field current/output to whatever I want. I monitor voltage, current, alternator temperatures.

Thanks for the reply. I don't really want something that I have to monitor and adjust.

At the moment I am thinking that simply using two 12vDC-24vDC 70A in/35A out chargers in parallel from the 12v lead acid starter battery to the LifePo4 bank might just be the easiest and safest way to do things. At a total of 140A load on a 175A 12vDC alternator that is 80% load so I may need a Mastervolt Alpha Pro III regulator too to keep the alternator temperatures down. I could also perhaps go to a Bosch 200A alternator that would then only be running at 70% load and perhaps this wouldn't need temperature control or wouldn't see so much of it at full output if a Alpha Pro regulator was fitted.

I imagine the losses in the DC-DC would probably mean only 60A @ 24vDC going to the LifePo4 but I imagine that that is pretty much what I would safely see out of a 100A 24vDC alternator anyway when it is temperature regulated.

 

[svsagres]

I just had a look back at the REC and now remember some of my reasons for diregarding it.

It only has passive balancing on the version needed for 24v systems and although I'm sure this works fine it seems very innefficient compared to active balancing.

Also the communication is a bit clunky compared to others. Having to buy additional software and a cable to plug in a PC seems rather backward in this modern world of blutooth apps.

Plus there does not seem to be a UK distributor shown on their site. I'm sure there was one before. Perhaps this is another benefit of Brexit that they never told us about?

Fair enough. I forget that I'm sticking with 12V, which means their BMS with active balancing is on the table. That said, if you initially balance your cells well, they shouldn't drift out too much over time, certainly enough that the passive balancing will be enough

As far as the setup goes, though, for me that's largely a one-and-done thing. The monitoring itself fires out over CAN Bus/NMEA 2000, so I'll be able to see the data I need on my other instruments and/or through the Cerbo. Yeah, the $60 or whatever it is for the software and RS485 adapter is a bit annoying, but *shrug* it's a fraction of a percent of what I'm spending on the whole thing. Furthermore, I think I can use the RS485 to change the configuration on the fly from within Node RED running on the Cerbo.

For me, the critical thing was the known good/working tight integration with both the Victron equipment I'm using elsewhere, and the Alternator. The flexibility of the Alternator controller is especially critical, given that I'm running a rather large alternator (80A) on an engine powered by a geriatric squirrel. (Yanmar 1GM10 installed in 1983).

 

[Smokin]

Hook it all up and let us know how it Goes. Man can't do anything right the first time.. LOL.

 

[bikesherpa]

Any progress on using the Alpha Pro with LFP?
I am looking at replacing my 24V 390Ah AGM battery bank with a 24V 560Ah LFP one using a REC BMS. I already have a Mastervolt Alpha Pro regulator and a 75A 24V alternator.
The Alpha Pro III has a Lithium setting, with programmable voltage and current levels. It also has an input terminal to shut off the alternator, which I am planning to connect to an output of the REC BMS for signaling a charge disconnect.
As anyone connected an Alpha Pro to the REC BMS?

 

[TimE]

That's interesting. The REC BMS has been recommended to me before but the price seemed a little eye watering compared to the JK BMS. Perhaps it has some features that make it worth the extra.

Perhaps a REC and a Wakespeed is something I should be looking into again.

If you are only using a standard 100A alternator, you are likely to be running it at no more than about 50A for longevity. You could keep the system simple with a JK BMS and send the alternator output to the start battery. Use multiple B2B chargers to charge the lithium off the engine battery whilst the engine is running. Super simple with resilience and redundancy