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**newhaul** · 26-09-2022, 19:09

Quote:

Originally Posted by goboatingnow

Yes one of the many

But there are easy alternatives to get around the inability of most BMS to handle cranking.

It’s also worth pointing out that many LFP s especially cheaper ones are 0.5C or 1C. Not suitable as engine start.

Hence 250ah lfp CALB cells when I built my bank several years ago .
But my engine only draws about 75 amps to crank its the glow plugs that draw 30 amps for 30 seconds . That is the biggie

goboatingnow · 26-09-2022, 19:12

Quote:

Originally Posted by newhaul

Mine does just fine and yes it has a bms that doesn't need to be bypassed to crank the engine. Sounds like the bms in your dropins is the weak link . My Daly is rated at 300 amp in and out .

Sure , but it’s cheap and simple to carry a separate backup Li jump start.

Secondly if you did switch in the LFP you now have to interlock out the SLA to avoid inadvertent paralleling , so it’s more complexity whereas a standalone jump start is simpler and probably cheaper.

**newhaul** · 26-09-2022, 19:25

Quote:

Originally Posted by goboatingnow

Sure , but it’s cheap and simple to carry a separate backup Li jump start.

Secondly if you did switch in the LFP you now have to interlock out the SLA to avoid inadvertent paralleling , so it’s more complexity whereas a standalone jump start is simpler and probably cheaper.

I also have a lfp jump bank it fits in my pocket .
BTW nothing happens by accident on my boat . I am a retired US Navy hull technician. Damage control was one of my specialties. I have backups for my backups.

goboatingnow · 26-09-2022, 19:35

Quote:

Originally Posted by newhaul

I also have a lfp jump bank it fits in my pocket .
BTW nothing happens by accident on my boat . I am a retired US Navy hull technician. Damage control was one of my specialties. I have backups for my backups.

I spent several years in the US in military electronics.

The design criteria for survivability under fire and subsequent recovery is entirely misplaced applied to leisure boats. We have to strike a compromise between costs , practicality but with emphasis on safety

This proposed approach emphasises safety first but addresses the ABYC and ISO recommendation that alternative power is available post bms battery shutdown.

This it does and it does it safely and protects against inadvertent operator stupidity.

The only point you made was about the starter and that’s easily solved by a cheap external jump start unit. Every boat should have one anyway as they are a great idea.

mcarthur · 26-09-2022, 19:49

GBN, on the diagram it seems (low res) to show a switch after the MPPTs, into the Lynx. Is that the disconnect? If so, can you explain the thinking as I thought a panel disconnect was between the MPPT and the panel, not between MPPT and distribution?

**newhaul** · 26-09-2022, 20:11

Quote:

Originally Posted by goboatingnow

I spent several years in the US in military electronics.

The design criteria for survivability under fire and subsequent recovery is entirely misplaced applied to leisure boats. We have to strike a compromise between costs , practicality but with emphasis on safety

This proposed approach emphasises safety first but addresses the ABYC and ISO recommendation that alternative power is available post bms battery shutdown.

This it does and it does it safely and protects against inadvertent operator stupidity.

The only point you made was about the starter and that’s easily solved by a cheap external jump start unit. Every boat should have one anyway as they are a great idea.

A couple specific points I use a grp 27 flooded lead acid battery FLA for starting not a sealed lead acid . SLA .

As to the jump pack we'll the main thing I noticed running my auto repair shop was that most of my jump calls were because their jump pack was dead as well . Most people don't remember to charge it periodically.

You still haven't answered my question as to why not to parallel my FLA with my LFP for cranking up the engine ?

**newhaul** · 26-09-2022, 20:14

Quote:

Originally Posted by mcarthur

GBN, on the diagram it seems (low res) to show a switch after the MPPTs, into the Lynx. Is that the disconnect? If so, can you explain the thinking as I thought a panel disconnect was between the MPPT and the panel, not between MPPT and distribution?

I missed that thank you for pointing it out and yes disconnect should be between the panels and the charge controller. Most state that in the installation instructions . Must keep battery connected if the panels are connected to protect from damage

**s/v Jedi** · 26-09-2022, 21:49

Quote:

Originally Posted by goboatingnow

Again Nick it consume 130 mA that’s nothing it doesn’t even get warm.

So let’s drop the making up stuff. It’s a very good compromise unit. Cost effective practical and above all fail safe. ( the RBS unit is not fail safe as i understand as it specifically stated it powers up in the previous state

Citation for powering up in previous state? It is auto-releasing, just like the solenoid, which isn’t fail safe either, plus it requires another manual switch in parallel for manual override, which is built into the RBS. The extra cabling added to the manual switch and you are at the same price.

130mA is nothing? Do you realize that this is a 24x7 load? It’s more than 3Ah per day for a relay! It’s also a 1.5W heating element, I can assure you that it gets hot.

**s/v Jedi** · 26-09-2022, 22:01

I held the diagram against ABYC recommendations and it appears that the manual switch violates 13.7.7

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

The switch clearly bypasses the protection relays.

rgleason · 27-09-2022, 16:24

Revision 9/27/2022, from the main discussion thread DIYsolarForum.com thread, Small Boat BMS/LFP Backup, post #343. This post also includes a PDF that is clearer, but not under the 2mb required here. Also included in the post is a drawio zip file.

**s/v Jedi** · 27-09-2022, 16:33

Quote:

Originally Posted by rgleason

Revision 9/27/2022, from the main discussion thread DIYsolarForum.com thread, Small Boat BMS/LFP Backup, post #343. This post also includes a PDF that is clearer, but not under the 2mb required here. Also included in the post is a drawio zip file.

Still appears to have MPPT breakers on battery instead of solar side. Also still missing the fuse on starter battery to Orion.

rgleason · 27-09-2022, 17:27

Quote:

Originally Posted by s/v Jedi

Still appears to have MPPT breakers on battery instead of solar side. Also still missing the fuse on starter battery to Orion.

MPPT are fused at the Lynx Bus and 15a inline fuses are shown at the device, but I think they are on the wrong wire, shouldn't those fuses be on the solar panel wires? Also I need a switch there? (You advised me sometime ago about this, and I will find that thread and your excellent direction.)

Next revision will have a fuse on starter battery to Orion. Thanks.

The Orion Tr is now switched on and off automatically.

Sorry but this forum reduces the quality of the jpegs. I may try to split the sheets SK-1 and SK-2 next time.

**s/v Jedi** · 27-09-2022, 17:33

Quote:

Originally Posted by rgleason

MPPT are fused at the Lynx Bus and 15a inline fuses are shown at the device, but I think they are on the wrong wire, shouldn't those fuses be on the solar panel wires? Also I need a switch there? (You advised me sometime ago about this, and I will find that thread and your excellent direction.)

Next revision will have a fuse on starter battery to Orion. Thanks.

The Orion Tr is now switched on and off automatically.

Sorry but this forum reduces the quality of the jpegs. I may try to split the sheets SK-1 and SK-2 next time.

It is handiest to use the solar DC breakers that go on a DIN rail. You can add some surge suppressors on the same rail. Yes, all that goes on the negative from the solar panels. The fuse at the Lynx is all you need for that wire.

I think the jog is good enough