Small Boat BMS/LFP with backup

[rgleason]

@wholybee wrote

My only change would be that there is no manual disconnect, and the Emergency switch allows paralleling of the batteries. So, I would change the emergency switch to a "1-2-off" type between the manual bypass and the lynx distribution.

Understood, one 3 way switch. I like it and will make that change.

1. LFP Bypass
2. Off
3. SLA Emergency
4. No both. Don't want to parallel the batteries (not compliant with ABYC.

@Goboatingnow wrote

With [the components shown] , ie. REC BMS , you have very fine control over charging limits , especially as you can

1. run DVCC on the Cerbo Gx
2. Control all Mppt and alternator charge sources , allowing central control.

What would be nice would to add the ability in the Cerbo to instruct the REC to reconnect the battery , this would even allow remote ( via victron VRM ) ability to reengage charge sources etc.

That would be something!

 

[rgleason]

Have made @wholybee's suggested change for an A-Off-B switch. Thank you, this makes it simpler.

 

[wholybee]

I was thinking more like this. So the "off" position becomes a complete battery disconnect. And the 1 / 2 positions select between the LFP and AGM without possibility of paralleling them.

 

[Goboatingnow]

I was thinking more like this. So the "off" position becomes a complete battery disconnect. And the 1 / 2 positions select between the LFP and AGM without possibility of paralleling them.

Yes but the diagram is more efficient and does the same thing

 

[Tribune]

Assuming the bypass to FLA is due to a BMS disconnect (open relay) with the bypass as shown, if there is any chance of the relay closing then there would be parallelling of the batteries. Wholybee's suggestion would prevent that. Or am I missing something?

 

[Goboatingnow]

Assuming the bypass to FLA is due to a BMS disconnect (open relay) with the bypass as shown, if there is any chance of the relay closing then there would be parallelling of the batteries. Wholybee's suggestion would prevent that. Or am I missing something?

That’s a good point. If so the original diagram always had that risk too.

But no BMS in my opinion should reconnect without manual command.

 

[Goboatingnow]

Actually thinking about this if the three way switch has the common connection to the load and each other terminal to the LFp battery or the SLA battery and you have no “ both option “ then you are safe even if the bms reconnects the LFP inadvertently , as the loads will be switched to the SLA.

So you need a off 1 , 2 no both combination switch
No situation results in inadvertent paralleling

This sort of thing

 

[rgleason]

While thinking about how to actually wire this, considering all the good points above, I think this switch is the right one provided there is a way to physically interupt power to the relay coil so that it becomes "normally open" when the switch is turned to SLA Emergency position.

This operation is ok if power to the relay is interrupted.

https://www.bluesea.com/products/6008200/m-Series_Selector_3_Position_Battery_Switch_-_Black

I found a Bluesea 1-off-2 with AFD (Alternator Field Disconnect) Switch that could be used to do this from the
e-series Selector 3 Position Battery Switch with AFD 11001 350v continuous, up to 32v, up to 4/0 awg



How does this look to you review experts?

NOPE! I realize now that wiring the relay coil power through the AFD would NOT solve the problem. There has to be a better way to do this.
When the switch is OFF the relay circuit (AFD) needs to be connected. (This is the opposite of an AFD circuit)
When the switch is on SLA Emergency the relay circuit (AFD) needs to be disconnected. (This is the opposite of an AFD)
When the switch is on LFP Bypass Override the relay circuit (AFD) can be connected or not, it does not matter.

Maybe we should ask Blueseas to make one?

Are there any simple and clever electrical engineering solutions available?
Of course wholybees wiring diagram would work nicely to meet the requirements (uses two switches)

 

[wholybee]

TBH, on my boat I would not have the switch to bypass the relay, only the 3 way selector. You should never bypass the relay without knowing what the cause of the failure is, which requires some investigation. So in an emergency, the correct action is to switch to the AGM.

 

[rgleason]

I understand the investigation of the cause of the relay disconnect is the first order of business, and switching to SLA Emergency is a reasonable thing to do, (knowing that the relay is disconnected and open) to provide light, navigation and power. Nevertheless, I would like it to have the setup unable to parallel the LFP and SLA, so to do that I need to interrupt the power to the rely when the switch is turned to SLA Emergency. I liked your idea of a single switch to do that, but will use two that are interlocked somehow if necessary.

There may be situations where investigation leads to the conclusion that there was a High voltage event or HVD in which case, if the LFP is still at high voltage, the most appropriate thing to do is to use the LFP Bypass Switch to allow the DC Panel to use the LFP until it is partially full. But in that situation, the SLA Emergency should not be connected.

 

[Goboatingnow]

There’s no need a simple three way switch with off, 1,2 with the common wired to the load /charge bus and one pin connected to the LFP , and the other to the SLA. When the SLA is selected it doesn’t matter if the BMS relay was activated as the battery

TBH, on my boat I would not have the switch to bypass the relay, only the 3 way selector. You should never bypass the relay without knowing what the cause of the failure is, which requires some investigation. So in an emergency, the correct action is to switch to the AGM.

i would beg to differ.

 

[Goboatingnow]

I understand the investigation of the cause of the relay disconnect is the first order of business, and switching to SLA Emergency is a reasonable thing to do, (knowing that the relay is disconnected and open) to provide light, navigation and power. Nevertheless, I would like it to have the setup unable to parallel the LFP and SLA, so to do that I need to interrupt the power to the rely when the switch is turned to SLA Emergency. I liked your idea of a single switch to do that, but will use two that are interlocked somehow if necessary.

There may be situations where investigation leads to the conclusion that there was a High voltage event or HVD in which case, if the LFP is still at high voltage, the most appropriate thing to do is to use the LFP Bypass Switch to allow the DC Panel to use the LFP until it is partially full. But in that situation, the SLA Emergency should not be connected.

Agreed. As a single switch what you need is a three way and to my knowledge no battery switch is three way.

What could be done is to use the alternator disconnect option to isolate the relay. Hence the relay cannot reengage

 

[rgleason]

Yes, that this would be good but it won't work right.

What could be done is to use the alternator disconnect option to isolate the relay. Hence the relay cannot reengage

Unfortunately, Blueseas e-series Selector 3 Position Battery Switch with AFD 11001 (correct link now)
works opposite to what we need with regard to the Alternator Field Disconnect.
When the switch is on Position 1 or 2, the AFD is connected and when in position OFF it is disconnected to protect the alternator.
We need the the AFD contacts to disconnect when on Position 2 (SLA Emergency) or both positions.

I could write Blueseas and ask about it. Meanwhile I think we need two switches as wholybee has shown.

https://diysolarforum.com/attachments/bypass-and-emg-switch-jpg.111911/.

Unless there is some other solution.

 

[rgleason]

LFP 3-way Emergency Switch with relay coil disconnect on Position 2

Written to Blueseas:

The 11001 has an AFD, which disconnects the field wire when OFF. I would like a different action.

I would like it to disconnect the wire when on Position 2. Is there such a switch?

I would like a switch intended for managing LiPoFe House Battery and Flooded Lead Acid Starter Batterys which allows me to safely switch to Starter Battery in the event of an emergency without paralleling the LiPoFe and the Flooded Lead Batteries as required by ABYC.

To accomplish this I need to wire the BMS relay coil control wire through a contact in a 3 way switch that disconnects the relay coil wire when the 3 way switch position 2 is selected.

Clarifiction - This has turned into a 4 way switch with RCD (relay coil disconnect)

NORMAL - Normal LFP Operation (relay coil wire is connected and BMS is operating normally)
Position 1 - LFP Bypass Relay Coil Switch (relay coil wire is disconnected)
Position 2 - SLA Emergency Backup (relay coil wire is disconnected to comply with ABYC requirements)
OFF - No Batteries (relay coil wire is disconnected to over-ride the BMS)

@svsagres @Goboatingnow @wholybee please review and advise. Thanks.

 

[Goboatingnow]

LFP 3-way Emergency Switch with relay coil disconnect on Position 2

Written to Blueseas:


Clarifiction - This has turned into a 4 way switch with RCD (relay coil disconnect)

NORMAL - Normal LFP Operation (relay coil wire is connected and BMS is operating normally)
Position 1 - LFP Bypass Relay Coil Switch (relay coil wire is disconnected)
Position 2 - SLA Emergency Backup (relay coil wire is disconnected to comply with ABYC requirements)
OFF - No Batteries (relay coil wire is disconnected to over-ride the BMS)

@svsagres @Goboatingnow @wholybee please review and advise. Thanks.

Yes that’s what you want. But I’d don’t beleive there’s a battery switch suitable

 

[Goboatingnow]

Yes, that this would be good but it won't work right.


Unfortunately, Blueseas e-series Selector 3 Position Battery Switch with AFD 11001 (correct link now)
works opposite to what we need with regard to the Alternator Field Disconnect.
When the switch is on Position 1 or 2, the AFD is connected and when in position OFF it is disconnected to protect the alternator.
We need the the AFD contacts to disconnect when on Position 2 (SLA Emergency) or both positions.

I could write Blueseas and ask about it. Meanwhile I think we need two switches as wholybee has shown.

https://diysolarforum.com/attachments/bypass-and-emg-switch-jpg.111911/.

Unless there is some other solution.

Yes correct the conventional alternator disconnects don’t suit this strategy.

 

[rgleason]

Response from Blueseas Technical:

Thank you for the question. The AFD is clocked at 11:00 and 1:00 so it will open when the rotor is between those two points.
Please ask if you have any additional questions.

To Blue Seas Technical:

4 way switch with RCD (relay coil disconnect)

NORMAL - Normal LFP Operation (relay coil wire is connected and BMS is operating normally)
Position 1 - LFP Bypass Relay Coil Switch (relay coil wire is disconnected) LFP is connected.
Position 2 - SLA Emergency Backup (relay coil wire is disconnected to comply with ABYC requirements) SLA is connected.
OFF - No Batteries (relay coil wire is disconnected to over-ride the BMS)
In this situation the disconnect of the relay coil wire has to occur around Position 1, Position 2 and OFF.
The relay coil wire is only connected when the switch is on NORMAL.
Position 1 provides connection to the LFP Battery (house).
Position 2 provides connection to the SLA Battery (start).

The reason this is needed is to provide a good single switch that meets ABYC requirements for LiFePo Batteries (SLA and LFP batteries are never paralleled) and provides safety and backup power in the event of a failure or emergency.

Do you have some suggestions for how we could accomplish making this switch?

Is there any way to reconfigure when the AFD is disconnected?

Later:

Yes you have explained what you need very well. And my apologies we do not have a switch that matches your needs.

 

[rgleason]

Now I am thinking that the Blueseas 11001 needs to be taken apart to see if the AFD disconnect can be changed to be at Position 2 for SLA Emergency. Someday I may try that, or perhaps the Guest switch that I have currently.

 

[rgleason]

Rod Collins has an excellent article Drop-in Lifepo be an educated consumer.

 

[wholybee]

ABYC requires a battery disconnect. I don't think that interrupting the relay coil satisfies that, but having 2 switches as I drew would.