LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[newhaul]

Originally Posted by Dockhead

I have dual alternators on the main engine, and my main and gen start systems are 12v.



So I can't "buffer" the second alternator with a start batt, nor would I want to eliminate the desirable total separation of these systems.


So I am planning to use one of these to protect the alternator:


https://sterling-power.com/products/...tection-device


Do you see any reason why this wouldn't work?

I'm sure it would work just fine for somebody but for me its the extra £50 that says no to me . Having a lead start battery serves that purpose quite well for my needs overall. That £50 will buy the winters diesel for my furnace .

[Dockhead]

Originally Posted by newhaul

I'm sure it would work just fine for somebody but for me its the extra £50 that says no to me . Having a lead start battery serves that purpose quite well for my needs overall. That £50 will buy the winters diesel for my furnace .

Well, I was not suggesting it for YOU!


£50 (actually £45) is a rounding error in a £4000 power system and would be cheaper IN MY PARTICULAR CASE than adding an otherwise useless sacrificial battery or adding more complexity to the wiring.


Does anyone see why this wouldn't work? It's only job is to save the alternator in the unlikely event of a high voltage cutoff event, which is last ditch protection of the battery in case for some odd reason the voltage doesn't get turned down by ordinary regulation. Might even be the second last ditch in case I can get the BMS (probably Batrium) to cut the field current first.

[newhaul]

Originally Posted by Dockhead

Well, I was not suggesting it for YOU!


£50 (actually £45) is a rounding error in a £4000 power system and would be cheaper IN MY PARTICULAR CASE than adding an otherwise useless sacrificial battery or adding more complexity to the wiring.


Does anyone see why this wouldn't work? It's only job is to save the alternator in the unlikely event of a high voltage cutoff event, which is last ditch protection of the battery in case for some odd reason the voltage doesn't get turned down by ordinary regulation. Might even be the second last ditch in case I can get the BMS (probably Batrium) to cut the field current first.

I know that you were asking about your case or generally so yes it would work great

[transmitterdan]

Originally Posted by Dockhead

Well, I was not suggesting it for YOU!


£50 (actually £45) is a rounding error in a £4000 power system and would be cheaper IN MY PARTICULAR CASE than adding an otherwise useless sacrificial battery or adding more complexity to the wiring.


Does anyone see why this wouldn't work? It's only job is to save the alternator in the unlikely event of a high voltage cutoff event, which is last ditch protection of the battery in case for some odd reason the voltage doesn't get turned down by ordinary regulation. Might even be the second last ditch in case I can get the BMS (probably Batrium) to cut the field current first.

Dockhead,

The “standard” solution is to use something like this along with a relay to disconnect the field (or regulator power) when HV disconnect is triggered. I would not use one of these alternator “zap-stop” devices without a field cut system. These alternator “protection” devices are generally designed for brief periods of over voltage not continuous use.

[Dockhead]

Originally Posted by transmitterdan

Dockhead,

The “standard” solution is to use something like this along with a relay to disconnect the field (or regulator power) when HV disconnect is triggered. I would not use one of these alternator “zap-stop” devices without a field cut system. These alternator “protection” devices are generally designed for brief periods of over voltage not continuous use.

Yes, as I posted in another thread:

Originally Posted by Dockhead

This isn't my thread, and I don't want to hijack it, but I answered these questions, with regard to my own particular installation.


Basically: I won't have lead available to serve this function, and the Sterling device is simpler and more elegant -- IF IT WORKS -- than installing a lead battery which has no other purpose, plus all the faff required to charge it properly since it doesn't use the same charge profile as lithium.


So the algorithm in my case would be:


1. Battery reaches target SOC -- go to float voltage [i.e. voltage sufficient to support loads without adding to SOC of the battery]
2. Battery high voltage condition -- shut down charge sources [backstop to 1 basically]
3. Battery high condition continues for 6 seconds after that -- trip the high voltage cutoff contactors [backstop to 2 basically].


Alternator protector is a backstop in case alternator regulator does not respond to 2 and the HVC contactor is tripped while the alternator is producing current.


Using a lead battery for this will be elegant in some system configurations, but not in mine.

Considering that I am no kind of EE (!), I would be grateful for comments to this.

[mbartosch]

Originally Posted by Dockhead

Considering that I am no kind of EE (!), I would be grateful for comments to this.

Forgive me if I did not fully catch the context of your query, but how about the following:

Assumption: you have a service battery, optionally a main contactor behind it (highly recommended), and from this (or the battery) a charge bus and a load bus, both separated from the battery or the main contactor via HVC and LVC contactors.
Main contactor, LVC and HVC contactors are controlled by the BMS. HVC and LVC occur before a main contactor disconnect.

Possible Solution for alternator protection:
Alternator B+ is connected to the main contactor or to the battery +, NOT to the charge bus
A HVC event cuts HVC contactor AND field to the alternator (e. g. via a normally closed relay)

Operation:
Stage 1: Normal operation. All contactors closed. Alternator B+ is connected to battery and charges battery. Charging sources are connected to the battery on charge bus and charge battery.
Stage 2: HVC is triggered. HVC contactor opens, normal charging sources are dropped off (e. g. solar panels) on the charge bus. Alternator stays connected to battery, because it's not on the charge bus (see above), but HVC NC relay cuts field to alternator. Alternator stops producing power.

Stage 3: Main contactor opens (emergency shutdown). BMS cuts all connectivity to the bank. Should not happen.

Hope this helps.

[john61ct]

Not to derail, but

Are the Victron mains chargers (finally!) the first "LFP ready" charge sources to specify

14.2V, 3.55Vpc Absorb?

rather than the usual 14.4 - 14.6V?

To add to the confusion, their docs conflate the LI label "Li-ion" with LFP / LiFePO₄

especially since they now sell packaged system LI / Li-ion (non-LFP)*batteries?

That chemistry at 4S charges to 16.8V, in some variants even 17.4V


"Storage Mode":

Whenever the battery has not been subjected to discharge during 24 hours, float voltage is reduced to 13.2V

This would be IMO **perfect** handling for LFP longevity

but that feature might **only** apply to lead chemistries,

_____
The deal breaker for me is a lack of user-custom setpoint adjustment, as featured in the solar controllers.

Probably best to keep discussion of the charger itself to that specific thread: http://www.cruisersforum.com/forums/...rs-223775.html

[newhaul]

Originally Posted by john61ct

Not to derail, but

Are the Victron mains chargers (finally!) the first "LFP ready" charge sources to specify

14.2V, 3.55Vpc Absorb?

rather than the usual 14.4 - 14.6V?

To add to the confusion, their docs conflate the LI label "Li-ion" with LFP / LiFePO₄

especially since they now sell packaged system LI / Li-ion (non-LFP)*batteries?

That chemistry at 4S charges to 16.8V, in some variants even 17.4V


"Storage Mode":

Whenever the battery has not been subjected to discharge during 24 hours, float voltage is reduced to 13.2V

This would be IMO **perfect** handling for LFP longevity

but that feature might **only** apply to lead chemistries,

_____
The deal breaker for me is a lack of user-custom setpoint adjustment, as featured in the solar controllers.

Probably best to keep discussion of the charger itself to that specific thread: http://www.cruisersforum.com/forums/...rs-223775.html

the problem with your hoped for 14.2v 3.55vpc is that most bms don't top balance till at the 3.6vpc point ( 14.4v) with hvc at 3.65vpc (14.6v)
so unless user Setable to go to the 14.4v it would not be useful for balancing . That is the primary reason personally for having a shore charger.
Will have to read the manual carefully.

Hereis is a link to the unit https://www.victronenergy.com/charge...t-ip65-charger

Comes in a variety of amp outputs up to 15amps

[CatNewBee]

You can configure the Victron to whatever you like. Starting from Li-Ion profile it disables temp compensation and equalization so you get a straight plain profile to your settings without the usual FLA whizardry.

[john61ct]

Originally Posted by newhaul

the problem with your hoped for 14.2v 3.55vpc is that most bms don't top balance till at the 3.6vpc point ( 14.4v) with hvc at 3.65vpc (14.6v)
so unless user Setable to go to the 14.4v it would not be useful for balancing

To rephrase - those who balance their cells using a non-adjustable BMS that can only do so at a very high voltage and/or a very slow rate,

must only use charge sources that

1. hold Absorb above that BMS' hard-coded start-balance voltage, **and**

2. allow AHT to be extended long enough for that BMS to finish balancing.

This is why I (personally) think it is silly to use such a BMS to do your balancing.

[john61ct]

Originally Posted by CatNewBee

You can configure the Victron to whatever you like.

Do you mean this specific unit?

If so, do you know if that Storage feature can be used with LFP?

That would overcome a **big** hurdle for me!

[newhaul]

Originally Posted by john61ct

To rephrase - those who balance their cells using a non-adjustable BMS that can only do so at a very high voltage and/or a very slow rate,

must only use charge sources that

1. hold Absorb above that BMS' hard-coded start-balance voltage, **and**

2. allow AHT to be extended long enough for that BMS to finish balancing.

This is why I (personally) think it is silly to use such a BMS to do your balancing.

well that is part of the purpose of having a bms .

What do you personally use on your lifepo4 house bank for top balancing ?

I use my custom configured bms with the top balancing feature .set to my specifications of 3.5vpc.

Its easy set it and forget it on the solar controller for the day. Just set mine to 14.40v.

[newhaul]

Originally Posted by john61ct

Do you mean this specific unit?

If so, do you know if that Storage feature can be used with LFP?

That would overcome a **big** hurdle for me!

reading the specifications sheet it doesn't mention lifepo4 in the storage feature description .
All it says wrt Lfp is this
Also charges Li-ion (LiFePO₄) batteries LiFePO₄ batteries are charged with a simple bulk – absorption – float algorithm

So I would say no it doesn't but with the low self discharge rate of Lfp you don't need a charger hooked up at all with less than a years layup ( IMO ymmv )

[CatNewBee]

Originally Posted by john61ct

Do you mean this specific unit?

If so, do you know if that Storage feature can be used with LFP?

That would overcome a **big** hurdle for me!

You can configure the values freely.

I can only speak for the units I use, the Quattro 12/5000 220 100/100 and the MPPT Smart Solar 150/100, but I do not see a reason why the other units, like the MultiPlus or the normal MPPT controllers would have different settings abilities, they use a similir UI and likely the same software.

For storage I simply change the settings to my needs. I am not aware of a second pre-set of parameters to switch back and forth between use and storage by a single setting.

Download the Victron Connect app and use the simulator, you can load any Victron Device and tweak the available settings. Also the configuration windows UI can be run in simulation mode for the inverters and chargers.

[john61ct]

We've been discussing exactly these points for some time now, there are dozens of non-balancing BMS out there, to be used by owners using any of the dozens of different kit designed to just do balancing.

Originally Posted by newhaul

I use my custom configured bms with the top balancing feature, set to my specifications of 3.5vpc.

If that configurable spec is the start-balance voltage, then you just adjust it to work in conjunction with whatever charge source and Absorb voltage you like, right?