Critique my LiFePo4 Plan!

[mbartosch]

Originally Posted by leandroflaherty

The starter battery is kept off and isolated with an on off switch, only used when motoring. Likewise the housebank, a renogy lifepo4 with built in bms, is turned off when motoring keeping the chemistry separate.
...
Keeps it simple, cheap and isolated if i run into any issues between the engine and home electrical systems. Only need to hit two battery switches to start and turn off the engine.

I see some downsides to this approach:
- if you forget to turn off the B2B charger after stopping the engine it will deplete your starter battery, leaving you with no (easy) way to start the engine again.
- there is no guarantee that the B2B does not draw more power than the alternator can produce, again possibly draining the starter battery.
- an extension of the above point: in the case of prolonged engine idling while charging the battery there may be additional problems. Even if the alt can cope with the power draw of the B2B at engine idle, it will possibly overheat due to the low RPMs on the alt fan. If it cannot cope, then again the starter battery is depleted.
- the setup is not very "other crew" friendly. The skipper may know how to operate things properly, but it is very easy to screw things up by flipping (or not flipping) a switch. Nothing I would trust non-technical crew or guests in.

Not saying you cannot do it that way, but if I had made the decision I would want some automation or failsafes to cater for these conditions.

[170122]

Simple, charge your lithium bank with the inverter and solar panels, feed your house, install a secondary charger to charge your Lithium house, and your Two Engine and windlass AGM , the one on the pictures will do both, then install an isolator one alternator 3 banks, this way it will charge you 3 banks, the house lithium will not be charged all the way up to 87% but will not damage them, the secondary charger will bring them at 100% on shore powers, or with your solar lithium controller

[leandroflaherty]

Good point, forgot to add I have a victron battery protect between the battery which cuts off the b2b if low voltage.


As for low charge from the alternator, non issue if you keep rpms above low rpms which is bad for diesels over extended times.


I single hand mostly, so crew is not that big an issue, but again, its VERY easy, just two switches. The b2b is in its own switch (not always on) and that is only used when i need it, which is not often as the solar and wind cover me 95% of the time.

[170122]

Non turbo Diesel engines are not affected by running the at idle, turbo engines will build up carbon deposits inside their aftercoolers..
Good Lithium batteries are now equipped with battery Managment systems that cut power on the negative side to protect them from low and high voltage, also to supervise every cell independently.
From the alternator positive go to the isolator in an from the isolator out go to each bank independently.
The solar will charge only the house.
The inverter will have to be programmed for 14.6 v charge, also only for the lithium bank.
AC power to the inverter from shore power, then from the inverter to the AC electrical panel.
Are you running air conditioning units, here is a 7000 BTU 12v DC running on just 25a on 12v DC

[mbartosch]

Originally Posted by Mabruteam

Good Lithium batteries are now equipped with battery Managment systems that cut power on the negative side to protect them from low and high voltage, also to supervise every cell independently.

The adjective "good" for LiFePO4 batteries with integrated BMS is debatable. See the many other threads about this topic.

From the alternator positive go to the isolator in an from the isolator out go to each bank independently.

This approach will chronically undercharge the LA battery, leading to premature failure due to sulfatation.

The inverter will have to be programmed for 14.6 v charge, also only for the lithium bank.

It seems to me that the majority of this community has commonly accepted that charging to 13.8 - 14.0 V (depending on personal taste, some may go even a little higher) will get the pack nearly to 100 % without possibly sacrificing battery life.
14.6 V is way too high in my opinion. By doing so you may be charging the LA battery properly but risking the costly LFP bank.

[roland stockham]

First this is not an area of expertise for me so I may be way off. 2 points I noted. The fact that you have issolation switches on both the fla batteries could set up a potential problem. If the BMS shuts down charge with both switches closef then the would be no battery in the curcuit and you would instantly blow the alternator diodes. Have you thought about wiring the start battery directly to the alternator. This would be a short lead probably in the engine bay so a minimal fire risk. Second point is that I thought the main advantage of Lithium was fast charging. You only show a 50 amp alternator. This would be undersize for anything over about 300a/hr even on fla's. The charge acceptance rate on a 600a/hr litium bank should be in the hundreds of a/hr so to take advantage of the substantial investment you are making I would think you want a small DC generator, say 2.5 to 3 kw or an ac set with a couple of very high power chargers. Otherwise cant see much advantage. If you just need it for high power devices like an electric stove it would probably be simpler and cheaper to fit a genset.

[170122]

if you want advice from a profesional building boats and equipment for over 35 years is up to you, I design and build lithium batteries for the marine industry, I design appliances to work with those batteries. I commented on this post because the advise given was wrong. Lithium batteries Iron phosphate are the best, not to confuse with Lithium Ion, they are much more stable on High and Low temperature, and they are green, the BMS must be incorporated into the battery, charge must be 14.6 v to bring them fully charged, If you have an alternator and 3 banks of batteries you must use an Isolator with one in and 3 out, the lithium batteries will not charge all the way because most alternators are not made for lithium,
Battery charge display showing 14.5 V on the images..

[170122]

I do not understand why some advisers over complicating the issue, Isolators like the one below is made out of diodes and rectifiers, power goes one way from the alternator to each battery bank, diodes prevent power to go back to the alternator. I run marine air conditioning on Lithium with plenty installations under my belt, I am able to run this 7000 BTU 4 hours on a single 31 series lithium..

Originally Posted by roland stockham

First this is not an area of expertise for me so I may be way off. 2 points I noted. The fact that you have issolation switches on both the fla batteries could set up a potential problem. If the BMS shuts down charge with both switches closef then the would be no battery in the curcuit and you would instantly blow the alternator diodes. Have you thought about wiring the start battery directly to the alternator. This would be a short lead probably in the engine bay so a minimal fire risk. Second point is that I thought the main advantage of Lithium was fast charging. You only show a 50 amp alternatormade . This would be undersize for anything over about 300a/hr even on fla's. The charge acceptance rate on a 600a/hr litium bank should be in the hundreds of a/hr so to take advantage of the substantial investment you are making I would think you want a small DC generator, say 2.5 to 3 kw or an ac set with a couple of very high power chargers. Otherwise cant see much advantage. If you just need it for high power devices like an electric stove it would probably be simpler and cheaper to fit a genset.

[170122]

Learning curve on aviation didn’t stop them to making reliable, same for Lithium batteries, most accidents came from do it yourself owners using old antiquated Lithium unstable UPS technology.. new Lithium Iron not Zion doesn’t compare, can you run a 7000 BTU air cond. on a 31 series AGM battery for over 4 hours? No, you will get max one hour, but we run one on A 31 series lithium battery for 4 hours every single day, the battery is not even warm after discharge, and recharge..
https://youtu.be/ehl2nt6isYc

Originally Posted by mbartosch

The adjective "good" for LiFePO4 batteries with integrated BMS is debatable. See the many other threads about this topic.



This approach will chronically undercharge the LA battery, leading to premature failure due to sulfatation.



It seems to me that the majority of this community has commonly accepted that charging to 13.8 - 14.0 V (depending on personal taste, some may go even a little higher) will get the pack nearly to 100 % without possibly sacrificing battery life.
14.6 V is way too high in my opinion. By doing so you may be charging the LA battery properly but risking the costly LFP bank.

[mbartosch]

Originally Posted by Mabruteam

Learning curve on aviation didn’t stop them to making reliable, same for Lithium batteries, most accidents came from do it yourself owners using old antiquated Lithium unstable UPS technology.. new Lithium Iron not Zion doesn’t compare, can you run a 7000 BTU air cond. on a 31 series AGM battery for over 4 hours? No, you will get max one hour, but we run one on A 31 series lithium battery for 4 hours every single day, the battery is not even warm after discharge, and recharge..
https://youtu.be/ehl2nt6isYc

Huh?

The TO does not have a air condition, nor does he have the plan to build a 31S LiFePO4 bank.

But very shiny products you are selling - and by the way, welcome to the forum.

[Qismat]

This thread went way off topic, and some of you clearly have no knowledge over lithium systems, or else didn't even read the first post/look at the outline.

Brutal.

[mbartosch]

Back to topic: if I take your diagram as the draft design which should be modified as little as possible, what I would do is:

Make sure the alternator does not experience sudden disconnect. In your diagram you have multiple failure modes:
- someone disconnects "House on/off switch"
- someone disconnects "Alternator charge breaker" (what's the purpose of this? do you want to connect this to the BMS for HVC?)

Possible solution: directly connect alternator B+ output to battery. Fuse this wire at the battery according to the wire maximum current specs. Directly connect alt B- to battery (not via the main contactor).

Provide proper shutdown for alternator power generation from BMS (HVC output should cut "ignition" input of MC614, some also advocate cutting supply power of MC614. Do not cut field directly.). You could do this with a N/O relay in the ignition wire to the MC614 triggered by HVC.

Have a separate connection from LiFePO4 + to House On/Off, fuse at battery according to wire current spec.

You don't have a HVC for the solar chargers and for the shore power charger (I assume the Xantrex is one) if I am not mistaken. Irritatingly you have a "Charge Bus" but for the LA batteries. I'd expect to see one for the non-inductive charge sources for the LFP bank.

I assume the 500 A relay at battery minus is the main contactor. If this is the only protection device for your setup (no separate HVC/LVC), a HVC event will also shut down house loads. Probably not what you want.

The input + side of the B2B charger should go to the house load bus, not directly to the battery.
As mentioned, it is beneficial to have house and load bus on a LFP setup, both with contactors controlled by the BMS.

The shunt belongs as close as possible to the house battery -. It must see all current flow in/out the battery to function properly (I don't know if the black wire from battery minus to MC614 is meant to be the B- of the alternator. If this is the case, the BMV7xx will not measure alternator charging).

[Qismat]

Originally Posted by mbartosch

Back to topic: if I take your diagram as the draft design which should be modified as little as possible, what I would do is:

Make sure the alternator does not experience sudden disconnect. In your diagram you have multiple failure modes:
- someone disconnects "House on/off switch"
- someone disconnects "Alternator charge breaker" (what's the purpose of this? do you want to connect this to the BMS for HVC?)

Possible solution: directly connect alternator B+ output to battery. Fuse this wire at the battery according to the wire maximum current specs. Directly connect alt B- to battery (not via the main contactor).

Provide proper shutdown for alternator power generation from BMS (HVC output should cut "ignition" input of MC614, some also advocate cutting supply power of MC614. Do not cut field directly.). You could do this with a N/O relay in the ignition wire to the MC614 triggered by HVC.

Have a separate connection from LiFePO4 + to House On/Off, fuse at battery according to wire current spec.

You don't have a HVC for the solar chargers and for the shore power charger (I assume the Xantrex is one) if I am not mistaken. Irritatingly you have a "Charge Bus" but for the LA batteries. I'd expect to see one for the non-inductive charge sources for the LFP bank.

I assume the 500 A relay at battery minus is the main contactor. If this is the only protection device for your setup (no separate HVC/LVC), a HVC event will also shut down house loads. Probably not what you want.

The input + side of the B2B charger should go to the house load bus, not directly to the battery.
As mentioned, it is beneficial to have house and load bus on a LFP setup, both with contactors controlled by the BMS.

The shunt belongs as close as possible to the house battery -. It must see all current flow in/out the battery to function properly (I don't know if the black wire from battery minus to MC614 is meant to be the B- of the alternator. If this is the case, the BMV7xx will not measure alternator charging).

This is fantastic, thank you very much! I've made some changes to the plan.

I do have a point, though - The BMS system I have has the connections for each of the cells, plus the main negative. There is also the B- and the C- connection... How can I wire a separate output to a HVC relay/LVC relay?
Or do I need a different more sophisticated BMS?

[Dockhead]

Originally Posted by witzgall

This is pretty simple, the BMS must just directly or indirectly (using a relay) cut the ignition wire to the regulator. This powers down the regulator, and the field is dropped gracefully protecting the alternator diodes.

If you are at all unsure about how to do this, please contact our technical support, they can help.

Chris

But the high voltage cutoff will interrupt the circuit in milliseconds. Cutting the field will not power down the alternator quickly enough to protect the alternator unless the BMS has a time delay between triggering the alternator shut-down and triggering the high voltage cutoff, and I haven't seen that feature on any BMS I've looked at.


The OP would be well served to have one of these:


https://www.sterling-power-usa.com/S...iondevice.aspx


In addition to wiring the system to cut the field of the alternator.

[Dockhead]

Originally Posted by mikedefieslife

. . . The BMS can control the MC-614, disconnecting either the brown or the red wire from the MC-614 will shut it down. In such instances there is no need for any other device. The alternator is safe. .

As I posted in another thread, I don't believe this is true. If the same signal is used to cut the field wire to the alternator which acuates the high voltage cutoff, the high voltage cutoff acts almost instaneously, whereas it takes a certain amount of time for the alternator to shut down. So you'll still zap the diodes.



I think you need an alternator protection device in addition to this.