Lithium and Alternators

[timohara]

Hi All

Lithium house batteries being charged by alternator... need some advice please !!

I will be limiting the number of Amps the 600Ah House Battery bank can draw from the alternator (rated at 125Amp max output) - in order to protect the alternator from over heating and going 'pop'.

At some point the batteries will reach max voltage and become full - at which point my batteries will be disconnecting the charge from the alternator - and the Amps will drop to nil.

However, I have somehow got it in my head that if the alternator is throwing Amps at the house batteries - and this is stopped quickly - and it drops to nil quickly - this can damage the alternator.

Does anyone know if this is correct ? Or offer any advice ?

Thanks

Tim

[smac999]

The batteries (bms). Shoukd not be disconnecting the alternator unless there is a problem. It won’t disconnect under normal use. If it’s disconnected you can blow up the alt. You need to find a way to prevent this if it happens.


How do you plan to limit the max current? Balmar reg with the belt manager?

[timohara]

Originally Posted by smac999

The batteries (bms). Shoukd not be disconnecting the alternator unless there is a problem. It won’t disconnect under normal use. If it’s disconnected you can blow up the alt. You need to find a way to prevent this if it happens.


How do you plan to limit the max current? Balmar reg with the belt manager?

Thanks.

I intend to leave the standard alternator in place - and use the Victron Smart BMS CL 12/100 - https://www.victronenergy.com/batter...urrent-limiter.

This will limit the current - to what ever max current I want. What do you think - this will do the job safely ? Victron seem to claim it is perfect for the solution and designed exactly for it.

[rgleason]

In the wiring diagram for the Victron BMS the alt is connected to the start battery I believe. This is exactly like several other good examples that use paralleled LFP and FLA/AGM start with a relay between to protect the LFP from overcharge and discharge.. This BMS is limited in alt charging to 80% of the max fuse of 100a.

[Maine Sail]

Originally Posted by timohara

Hi All


At some point the batteries will reach max voltage and become full - at which point my batteries will be disconnecting the charge from the alternator - and the Amps will drop to nil.

A BMS does not disconnect on batteries based on SoC or being at 100% SoC. The only way a BMS disconnects is on over-voltage (pack or cell), under-voltage (pack or cell) over temp, BMS over current, BMS over temp. A stock alternator will be very happy to continue charging your LFP pack and holding it its its max voltage indefinitely, which is not good for LFP. You want to make darn sure your stock alterntor cannot exceed the safe pack voltage. A BMS is an insurance policy to protect the cells from the items listed above, not a cell manager to be used for managing charging.

If your alternator can charge the LFP bank beyond its disconnect voltage, convert it to external regulation.

Originally Posted by timohara

However, I have somehow got it in my head that if the alternator is throwing Amps at the house batteries - and this is stopped quickly - and it drops to nil quickly - this can damage the alternator.

Not just the alternator, anything connected to the house bus, that is sensitive to voltage transients, including your marine electronics can be damaged.

[timohara]

Thanks Maine Sail - I get it. Back to the drawing board.

[Deividas]

There is my idea of how to solve this problem. I'm planning to use B2B charger to separate LiFePo4 house bank from the alternator and to limit Amps that house bank will take because I'm going to use my standard 60Amp alternator.

[rgleason]

Please see this post. Timohera has been cross posting on the same topic. Thanks.


Deividas what you have is a Dual port / Dual Relay system which separates the charge and discharge buses, like the examples above.
You will want a dual port BMS, and some of those are limited on the current/amps on the second port.

[CarlF]

I'm hardly an expert but this is what my research has shown.

Yes - you are right to worry about the BMS disconnecting and frying your alternator diodes (and other surge issues) I'm assuming you are putting in a drop-in lithium.

The BMS disconnect is a failsafe. It should not disconnect in normal charging. Instead your alternator regulator should reduce the voltage to a float voltage that meets the specs for your drop-in lithium's float. This means an external alternator regulator where voltages can be set. Some battery companies will deny a warranty claim if there's evidence that your BMS was routinely disconnecting.

The best solution is to have a BMS that communicates with the alternator regulator and shuts down the alternator before a disconnect. Most drop in batteries don't have this capability. Lithionics is an example of one that does.

An alternative is to keep a conventional battery in the circuit. A common solution is to have an AGM start battery as many drop-in lithium batteries can not be used for engine start. As mentioned above, install a VSR between the start and lithium banks that will parallel the two banks whenever the alternator is charging and the batteries are above about 13.4V. Most drop-in lithiums and AGM batteries have very similar charge voltages. The AGM's won't be hurt charging at the drop-in Lithium voltages. Don't use temperature compensation.

And whatever method you use also install a "zap stopper" on the alternator as a backup. The best one appears to be the Sterling Alternator Protector.

All that said, it's best to use an electrician who's installed a lot of lithium systems. Or at least have him review it. There are gotchas.

[Knotical]

Take a look at Calico Skies’ latest video where they converted to lithium, Bill explains the process in detail (more towards the end of the video), he will even answer your question/s in the comments.

https://youtu.be/X5iKZbIUlEY

[Pete7]

Originally Posted by Knotical

Take a look at Calico Skies’ latest video where they converted to lithium, Bill explains the process in detail (more towards the end of the video), he will even answer your question/s in the comments.

Wow, they have just been given 6 x 2 year old lithium batteries from Delos. Great Christmas present.

Pete

[Wood]

Originally Posted by timohara

Hi All
Lithium house batteries being charged by alternator... need some advice please !!<snip>

An potentially economic alternative is the Sterling Alternator/Battery Charger:
https://sterling-power.com/products/...ers-up-to-130a
.
I picked one up used on ebay for $75US

It will charge the LiFePO4 with a 3 stage charge and has a number of configuration settings. I'm using AGM1 @ 14.1v bulk & 13.4v float. It .charges the start bank separately - so it the lithium charge bus disengages there is still load on the alternator

My lithium bank is 560AH. The alternator is OEM 1989 80amp. The most the batteries have ever drawn is 50amps tapering to 20 or so before the battery reaches 13.8 volts. I've never gotten a full charge on the alternator [nor to I want to]. I generally cruise at least 6 hours runs up to maybe 10 hours. So the chance of dropping to float for any long period is slim.

[scfoster]

Timohara, going through the same process.
Have 300Ah BattleBorn LiFePO4 house bank and Balmar alternator with external regulator.
You are correct that you will damage the alternator when the BMS shuts off charging to the LI bank.
Not sure where you're located. I can't recommend Peter Kennedy at PKYS.com enough.
Spoke with him yesterday to weigh options. For my needs, I've ordered a 170A Balmar alternator with a new MC 614 regulator. Will charge the starter battery and forward bow-thruster/windlass battery. Then will use Victron DC-DC chargers in parallel to charge the LI house bank.
Already have Victron equipment, so that works for me.

Again, everyone's situation is different, so it helps to talk it through with an expert who understands ABYC requirements.

Here's a video that may be helpful. Advance to 35:50 where the CEO of BattleBorn talks about charging LI from alternators.

https://www.youtube.com/watch?v=21Ql...ature=emb_logo