Small Boat BMS/LFP with backup

[rgleason]

John Harries has reviewed the diagram above and found a problem with the starter wiring:

1. SLA Battery needs a 250a fuse.
2. Wire from SLA Battery to the starter should be 2/0 awg
3. To support the starter loads for "3YM30 Starter 64a min with Max load current 250a and 400CCA load minimum".

He also focused on SLA Emergency Feed at 100a.

1. The dashed red SLA Emergency Feed to the DC Panel and Chargers was fused 100a and sized for emergency condition DC Panel loads.
2. I now realize now that we have the Alternator also recharging the SLA when the 1-Off-2 switch is on the SLA Emergency position.
3. The Wakespeed under these emergency conditions (with the BMS dark and unpowered) will just output 13.8 volts. Is it really necessary to increase this wire to 2/0? LATER: SLA 100ah x 25% acceptance = 20 amps, so sizing red dashed for 100a is ok.
4. Additionally we plan to depower the Alternator to 100-120a in all modes, but with the switch in Off “Normal BMS/LFP” mode we have sized the alternator wires for the full 160a Alternator output.
5. Incidentally, in SLA Emergency Mode with no LFP, any brownouts and spikes when starting the engine, can be solved by shutdown of all equipment for a brief period, if this is thought to be a problem. At sea, this is definitely a consideration.

Thanks John for catching this.

One more note. John points out that we have not separated essential navigation loads from non-essential, and powered the essential loads from a different battery than LFP. He is correct. Instead for this small boat we have provided:
1. When BMS/LFP shutdown and the boat goes dark, a single switch is provided to power the DC Panel from the SLA.
2. Non-essential DC Panel loads can be manually switched off such as refrigeration, autopilot, etc.

I will be making another diagram soon, once we figure out the answer to the emergency feed wire size and fuse.
I need to add to the ABYC compliance list, strapping down the batteries and advance notice of shutdown by alarm.
Also I note that the BMS manufacturer and type need to be labeled, and I should put together an equipment and cost list.

 

[Goboatingnow]

In relation to point 5 in reality there’s not much you can do other then manually sequence loads with engine start. I would contend this is acceptable since this is a manual override mode.

 

[rgleason]

Agreed, any thoughts about the size of the SLA Emergency dashed red feed with respect to Alternator Charging?

Also ( @svsagres and @wholybee ) when the switch is on LFP Disconnect and SLA Emergency:

1. Can all modes of charging (alternator and solar) able to be switched on/off via CerboGX? (keeping in mind the CerboGX is powered by SLA.)
2. Obviously all discharge equipment can be controlled via the DC Panel breakers.
3. The Wakespeed under these emergency conditions (with the BMS dark and unpowered) will just output 13.8 volts. Is there any way to easily override that to provide more power and charge the SLA properly, perhaps through the CerboGX or the bluetooth interface? In that case the 2/0 wire would be needed.
4. We have the BMS canbus wire connected to one of the Wakespeed canbus ports and then the other canbus port connects to the CerboGX, so when the BMS goes dark on LFP disconnect via the main relay, the Wakespeed - CerboGX canbus connection will still be live won't it?

 

[Goboatingnow]

Agreed, any thoughts about the size of the SLA Emergency dashed red feed with respect to Alternator Charging?

Feed to starter should be AWB 3. alternator and fused suitable. Many starters are not fused. Alternator feed should be separate to battery , sized for max expected alternator output and seperately fused to protect that wire at the battery.

Also ( @svsagres and @wholybee ) when the switch is on LFP Disconnect and SLA Emergency:

1. Can all modes of charging (alternator and solar) able to be switched on/off via CerboGX? (keeping in mind the CerboGX is powered by SLA.)
2. Obviously all discharge equipment can be controlled via the DC Panel breakers.
3. The Wakespeed under these emergency conditions (with the BMS dark and unpowered) will just output 13.8 volts. Is there any way to easily override that to provide more power and charge the SLA properly, perhaps through the CerboGX or the bluetooth interface? In that case the 2/0 wire would be needed.
4. We have the BMS canbus wire connected to one of the Wakespeed canbus ports and then the other canbus port connects to the CerboGX, so when the BMS goes dark on LFP disconnect via the main relay, the Wakespeed - CerboGX canbus connection will still be live won't it?

Yes the can bus will be live

 

[svsagres]

Agreed, any thoughts about the size of the SLA Emergency dashed red feed with respect to Alternator Charging?

Also ( @svsagres and @wholybee ) when the switch is on LFP Disconnect and SLA Emergency:

1. Can all modes of charging (alternator and solar) able to be switched on/off via CerboGX? (keeping in mind the CerboGX is powered by SLA.)
2. Obviously all discharge equipment can be controlled via the DC Panel breakers.
3. The Wakespeed under these emergency conditions (with the BMS dark and unpowered) will just output 13.8 volts. Is there any way to easily override that to provide more power and charge the SLA properly, perhaps through the CerboGX or the bluetooth interface? In that case the 2/0 wire would be needed.
4. We have the BMS canbus wire connected to one of the Wakespeed canbus ports and then the other canbus port connects to the CerboGX, so when the BMS goes dark on LFP disconnect via the main relay, the Wakespeed - CerboGX canbus connection will still be live won't it?

In my system, at least, I just let it all go into limp mode. It doesn’t need to be fully functional, just needs to get me back to civilization. It’s unlikely to ever happen, so I’m not worried about it in the slightest. I just keep a length of terminated 2awg that I can jumper between the alternator and starter. Easy peasy, and I’ll probably never ever use it.

 

[rgleason]

Feed to starter should be AWB 3. alternator and fused suitable. Many starters are not fused.

Perhaps I am confusing things here, but I think the Starter feed from the SLA Battery should be a separate 2/0 awg wire. You advise that "many starters are not fused" and mine is not right now, so I am not going to use a fuse.

Alternator feed should be separate to battery , sized for max expected alternator output and separately fused to protect that wire at the battery.

Yes I think I need a 250a fuse at the SLA Battery, but why can't I use the red dashed SLA emergency wire shown in the diagram because all the chargers including the alternator are on the Lynx bus. I guess I should size it as 2/0 even though its never going to be above 100a and until I figure out if I can actually charge the SLA (70ah max battery x 25% acceptance= <20A) with the right profile when using the SLA as emergency battery it will only be charging at acceptance 13.8v level.

Looking at SK-2 (second page), there is an electron route from the chargers to the lynx bus, through the 1-Off_2 Switch "SLA Emergency Position" to the SLA Battery Positive. (I realize now that I moved the DC Panel to the Lynx bus.) So that red dashed wire should be 2/0 and be a separate wire to the battery with a 250a fuse?

Because the canBus from Wakespeed to CerboGX will be powered I think that there may be an easy way to reprogram the regulator on the fly, either through the CerboGX or via bluetooth App.

@svsagres

..limp mode. .. just needs to get me back to civilization. .. just keep a length of terminated 2awg that I can jumper between the alternator and starter.

Understood. I guess I'd rather not mess around in the tight engine room with a jumper cable at night.... something bad might happen. LATER: Also I might want to actually charge the battery and turn off the engine and sail, due to the distance.

 

[svsagres]

Understood. I guess I'd rather not mess around in the tight engine room with a jumper cable at night.... something bad might happen.

Well, I’ll probably never have to do that in anger as even if my system takes a dump, my engine will keep going and since I use my iPad as a chart plotter, it can get me into a safe anchorage to deal with.

 

[Goboatingnow]

Just to clarify

SLA to battery #2 AWG. This has not been historically fused

Alternator to battery is sized for max alternator current and is usually something like #8 or #10 depending on max alternator capability. This should be fused to the wire capacity at the terminating battery connection point. Certainly unless you have a massive alternator there’s no need for #2

The “ dotted red line is supplying the boats loads and needs to sized appropriately depending on load current expectations. Fused again to protect the wire

 

[rgleason]

Here is the Sept 26, 2022 revision, with recalculated wiring sizes & lengths, starter and SLA revisions, and additional notes.

Does the boat ground from the Lynx BMS to the Engine really need to be 1/0?

 

[Goboatingnow]

Here is the Sept 26, 2022 revision, with recalculated wiring sizes & lengths, starter and SLA revisions, and additional notes.

Does the boat ground from the Lynx BMS to the Engine really need to be 1/0?

Seems excessive what’s the total peak current the lynx is carrying

View attachment 113646

 

[rgleason]

I think the Lynx Bus total peak current would be one of these:
1. Chargers Alternator (field restricted - belt managed) 100a + Solar 15a - DC Panel 10a = 105a (3 AWG 16' 2 AWG 20')
2. Chargers Alternator (full field - no belt management) 160a + Solar 15a - DC Panel 10a = 165a (1/0 AWG 21' )

I really doubt that #2 will ever occur, but perhaps that is what I have to do to comply with electrical standards?

 

[rgleason]

The newest version of the Wakespeed WS500 uses the VE.Can bus for connection to the CerboGX

13. Wakespeed WS500 support

www.victronenergy.com

From a Victron Forum

Overview:
The REC BMS can form an integral part of a networked Victron Energy System by working together with your inverter, MPPTs and chargers to help avoid hard shutdowns.

See this post please also this one and this one

The REC BMS functionally acts as a Master DC source on the CANBus network via the Cerbo, and becomes part of the Victron Ecosystem. You just need to set a few parameters in your Cerbo to use the REC as your main DC supply. I have attached a few page snippets showing what the REC BMS looks like in a Victron VRM and Cerbo. With this setup the REC BMS, as the cell approaches a high voltage condition, will send a CANBus maximum current/voltage setpoint to your MPPT, MultiPlus, and the WS500. This will work as a high limit function and start to pull back the charging of all smart charging devices attached. The WS500 will actually get the signal directly from the REC BMS, based on the CCN setup parameters of your WS500, so it does not need to be fully compliant with rest of the Victron devices. You just wont be able to see the WS500 parameters and alarms on your Cerbo yet. (But it should be available in a future release in the next year or so, I would guess.)

What does this all mean? The premise here is that with an integrated system you can modulate your "Smart" charging devices to avoid a hard OV trip. Even better, it will throttle the output to allow your cells to top balance without nuisance trips. For instance, lets say you have one cell that hits 100% before the others. With a conventional system, your overall voltage is still telling your chargers to charge, but the BMS will have to issue a hard OV trip to save that cell. In a "Smart" configuration, the REC BMS throttles back all of your Smart charging controllers, to allow the out of balance cell to top balance and remain within the normal range, while the others slowly top up.

You will need a couple of cables to do this.
REC BMS to Victron Cerbo: https://www.offgridsoftwaresolutions.com/product/rec-victron-canbus-cable/
WS500 to Victron Cerbo: https://www.offgridsoftwaresolutions.com/product/rec-ws500-canbus-cable/
And if you dont have a Victron system and just want to connect your WS500 to your REC BMS directly: https://www.offgridsoftwaresolutions.com/product/rec-ws500-canbus-cable/

Note that the above list has changed recently because the new version of the WS500 is now using the CerboGX VE.Can cable.

 

[Goboatingnow]

The one thing that needs addressing is in emergency mode The Orion is connected to itself !!!

 

[rgleason]

Yes, I've got that covered under Procedures, that the DC-DC charger has to be turned off at the DC Panel manually otherwise it is a runaround circuit (I don't think it would hurt anything, and maybe the battery would actually get charged rather than sitting at 13.8v, but then the regulator would back off and not do absorption charging at all).
But recently I saw your post about automatically disconnecting the DC-DC charger with the switch AFD?
Would running the DC-DC Charger switch through the smaller NC relay (or even a second NC relay) make it automatic?

I am going to just pick

1. Chargers Alternator (field restricted - belt managed) 100a + Solar 15a - DC Panel 10a = 105a (3 AWG 16' 2 AWG 20')

Unless you think I should go to 1/0 AWG for a safer circuit.

Also the note for 1-Off-2 Position 2 has to be changed to be like Position 1 with the NC powered on and open, BMS NO relay depowered.

Regarding the statement that this switch is bypassing the protection relays and is against

13.7.7 No electrical connections should be made directly to a lithium ion battery that would bypass a BMS or the protection relays.

1. I believe context is important. It does bypass the protection relays when on "LFP Bypass Override", however "Off Normal LFP Operation" and "SLA Emergency Feed & LFP Disconnect" does not.
2. The LFP Bypass Override is there to allow charging which is necessary to get the batteries back on line in the event of a LVD shutdown.
3. As I said earlier, I am not going to be horsing around sailing on a dark night, with a dark boat, when singlehanded with jumper cables trying to get discharged LFP charging!

 

[Goboatingnow]

Yes, I've got that covered under Procedures, that the DC-DC charger has to be turned off at the DC Panel manually otherwise it is a runaround circuit (I don't think it would hurt anything, and maybe the battery would actually get charged rather than sitting at 13.8v, but then the regulator would back off and not do absorption charging at all).
But recently I saw your post about automatically disconnecting the DC-DC charger with the switch AFD?
Would running the DC-DC Charger switch through the smaller NC relay (or even a second NC relay) make it automatic?

I am going to just pick

Unless you think I should go to 1/0 AWG for a safer circuit.

Also the note for 1-Off-2 Position 2 has to be changed to be like Position 1 with the NC powered on and open, BMS NO relay depowered.

Regarding the statement that this switch is bypassing the protection relays and is against

1. I believe context is important. It does bypass the protection relays when on "LFP Bypass Override", however "Off Normal LFP Operation" and "SLA Emergency Feed & LFP Disconnect" does not.
2. The LFP Bypass Override is there to allow charging which is necessary to get the batteries back on line in the event of a LVD shutdown.
3. As I said earlier, I am not going to be horsing around sailing on a dark night, with a dark boat, when singlehanded with jumper cables trying to get discharged LFP charging!

The standards do allow manual override on extremis. So I believe you are compliant because in normal mode with the switch to “ off” you have nothing connected to the battery terminals except the bms.

Hence its fine

The AFD relay is in essence a “ emergency mode is active “ signal. Hence you could use multiple relay contacts to interlock other units like the Orion.

 

[rgleason]

Great. I can show that improvement next.

I think I should change the label to "LFP Bypass Override - Used for LVD to enable charging."

I had an idea. When the BMS/LFP disconnects is there a way to get it to automatically shift to SLA Emergency so navigation and lights are not interrupted and no manual operation is needed? Or is that too complicated?

 

[Goboatingnow]

Great. I can show that improvement next.

I think I should change the label to "LFP Bypass Override - Used for LVD to enable charging."

I had an idea. When the BMS/LFP disconnects is there a way to get it to automatically shift to SLA Emergency so navigation and lights are not interrupted and no manual operation is needed? Or is that too complicated?

Getting a bit complicated for an event that should never happen. Your Cerbo should be screaming at you long before LVE disconnect.

 

[rgleason]

Revisions are, improvement to 1-Off-2 Switch, automatic on/off of Orion Tr depending on Switch position, clarifications regarding ABYC and labeling.

 

[rgleason]

We need a fuse on starter battery to Orion-Tr.
Also move the inline 15a fuses on MPPT up to just before the Lynx
Also need solar DC breakers can be on a DIN rail with surge suppressors, all that goes on the negative from the solar panels

 

[Goboatingnow]

We need a fuse on starter battery to Orion-Tr.
Also move the inline 15a fuses on MPPT up to just before the Lynx
Also need solar DC breakers can be on a DIN rail with surge suppressors, all that goes on the negative from the solar panels

Can never see the point of dc breakers on the solar

 

[svsagres]

Can never see the point of dc breakers on the solar

It makes sense for large current, high voltage arrays... for what we can fit on a small boat? Yeah, just disconnecting the MC4s is adequate. I'm using 24V panels, so my Voc is 36V or so, which is safe to handle. It would be different if I was running 72Voc or higher.

 

[rgleason]

Thanks. @svsagres @Goboatingnow

Yes, I've been disconnecting the the MC4's before hurricanes, with our new dodger SunPower panels. Its only 100w right now.
Two SunPower 50w + Two Sungard Controllers

Photos of installation:

Illustrated Guide to Solar Installations on Boats - Cruisers & Sailing Forums

Goal of this thread: Show multiple photos of solar panel installations on boats (sail or power) along with some descriptive text to identify the type of installation , location, effectiveness, and

www.cruisersforum.com

They are easily stowed before tropical storms and hurricanes, at some point before installing lithium I will change to MPPT controllers that are mounted inside where it is dry!

However don't I need to have some 5a fuses in the Solar Panel circuits?

LATER: When to fuse a Solar Panel Array.

Model SPR-E-Flex-50​

Nominal Power (Pnom) 50 W​

Power Tolerance +/–3%​

Rated Voltage (Vmpp) 18 V​

Rated Current (Impp) 2.8 A​

Open-circuit voltage (Voc) 21.5 V​

Short-circuit current (Isc) 3.0 A​

Power Temp Coefficient –0.35%/° C​

Voltage Temp Coefficient –58.9 mV/° C​

Current Temp Coefficient 2.6 mA/° C​

Max. System Voltage 45 V​

Series Fuse Rating 15 A​

​

LATER: Goboatingnow statement: https://www.cruisersforum.com/forum...i-reference-diagram-268921-2.html#post3685204

Also I think I will use the Lynx bus differently now. The MPPT wiring to the Lynx will be a dual set of wires up to the center +/- posts that don't support a fuse. I will then provide two inline 15a fuses just below the Lynx. I think this is more acceptable wiring.

The Orion Tr Charger can then be moved to the free fused +/- on the Lynx since we now have it automatically turned on when the Switch Position is in Off - LFP Normal. I still need to show a fuse at the battery.

Question: Isn't the RBS switch the same function as the "LFP Override" in the 1-Off-2 Switch above?

From the link above:

Keep in mind that any component can fail. I see the argument that when the BMS fails, the non-latching solenoid will open, protecting the battery. This argument is brought like if it is an advantage. Now imagine a battery that is 100% okay and the BMS fails, taking this good battery offline preventing you from hauling anchor during a violent squall that threatens to throw you on the rocks. The supposedly safety mechanism has turned into a disaster.

With the RBS, you can manually switch it off.

Likewise, instead of the BMS failing, the solenoid can fail. Imagine a massive power draw from the inverter and the BMS detects low voltage in cells and triggers LVC, but the solenoid contacts fuse together as they try to interrupt the large current.

For MOSFET based BMS’s it’s the same because MOSFETs normally fail in a shorted state.

Dealing with failing technology is a thing to consider. I like the RBS because it allows manual operation, even a lockout function, as well as remote switch and remote control by microcontroller. I also like the switch indicator signal that allows the microcontroller to learn the switch state. You can write a software routine that closes or opens the switch intelligently, instead of just sending a signal and pray it works.

What Jedi (Nick) says "With the RBS, you can manually switch it off." What he means is actually "Override the BMS". According to him this is in violation of

13.7.7 No electrical connections should be made directly to a lithium ion battery that would bypass a BMS or the protection relays.

 

[Goboatingnow]

It makes sense for large current, high voltage arrays... for what we can fit on a small boat? Yeah, just disconnecting the MC4s is adequate. I'm using 24V panels, so my Voc is 36V or so, which is safe to handle. It would be different if I was running 72Voc or higher.

It makes no sense to use fuses. The wire must be sized for Isc. The fuse must be at least Isc. There are no conditions when the fuse will ever blow.

 

[Goboatingnow]

Thanks. @svsagres @Goboatingnow

Yes, I've been disconnecting the the MC4's before hurricanes, with our new dodger SunPower panels. Its only 100w right now.
Two SunPower 50w + Two Sungard Controllers

Photos of installation:

Illustrated Guide to Solar Installations on Boats - Cruisers & Sailing Forums

Goal of this thread: Show multiple photos of solar panel installations on boats (sail or power) along with some descriptive text to identify the type of installation , location, effectiveness, and

www.cruisersforum.com

They are easily stowed before tropical storms and hurricanes, at some point before installing lithium I will change to MPPT controllers that are mounted inside where it is dry!

However don't I need to have some 5a fuses in the Solar Panel circuits?

Also I think I will use the Lynx bus differently now. The MPPT wiring to the Lynx will be a dual set of wires up to the center +/- posts that don't support a fuse. I will then provide two inline 15a fuses just below the Lynx. I think this is more acceptable wiring.

The Orion Tr Charger can then be moved to the free fused +/- on the Lynx since we now have it automatically turned on when the Switch Position is in Off - LFP Normal. I still need to show a fuse at the battery.

Question: Isn't the RBS switch the same function as the "LFP Override" in the 1-Off-2 Switch above?

From the link above:


What Jedi (Nick) says "With the RBS, you can manually switch it off." What he means is actually "Override the BMS". According to him this is in violation of

Nick only ever listens to himself. !!!

13.5.3 Consideration should be given to providing alternative power for critical systems (e.g., engine starting,
navigation lights, etc) if a BMS shuts down the battery.

I would argue this gives grounds for a manual override

 

[Goboatingnow]

Thanks. @svsagres @Goboatingnow

Yes, I've been disconnecting the the MC4's before hurricanes, with our new dodger SunPower panels. Its only 100w right now.
Two SunPower 50w + Two Sungard Controllers

Photos of installation:

Illustrated Guide to Solar Installations on Boats - Cruisers & Sailing Forums

Goal of this thread: Show multiple photos of solar panel installations on boats (sail or power) along with some descriptive text to identify the type of installation , location, effectiveness, and

www.cruisersforum.com

They are easily stowed before tropical storms and hurricanes, at some point before installing lithium I will change to MPPT controllers that are mounted inside where it is dry!

However don't I need to have some 5a fuses in the Solar Panel circuits?

No. The wiring is sized for Isc

Also I think I will use the Lynx bus differently now. The MPPT wiring to the Lynx will be a dual set of wires up to the center +/- posts that don't support a fuse. I will then provide two inline 15a fuses just below the Lynx. I think this is more acceptable wiring.

The Orion Tr Charger can then be moved to the free fused +/- on the Lynx since we now have it automatically turned on when the Switch Position is in Off - LFP Normal. I still need to show a fuse at the battery.

Question: Isn't the RBS switch the same function as the "LFP Override" in the 1-Off-2 Switch above?

No stop second guessing yourself Nick tends to only beleive his is the correct viewpoint

The RBS has a manual override but it has no way to go connect in the SLA. So now you need another switch ( like you had before ) now you again have the issue of protecting the SLA from inadvertent paralleling because the rbs relay could fail latched on

From the link above:


What Jedi (Nick) says "With the RBS, you can manually switch it off." What he means is actually "Override the BMS". According to him this is in violation of

Yes he’s contradicting himself