Safe to relly on LifePO4's BMS to protect the wire from battery to switch?

[CaptainRivet]

Originally Posted by gsalgado

My windlass is a Maxwell 1200W. Battery is a drop in replacement, Ampere Time 12v 300AH

MRBF Interrupt Capacity: 10000A @ 14V DC

highly recommend not to use this for the windlass.
1200W is 140A cont and peaks to 500A. your battery can do short-term at best 400A. the 200A cut off is realized by mosfets which get easily blown by surge and reverse current that a motor can create. then the whole battery is dead. You have a house LFP with quite low spec cells. that's made for low continues C rates but not high surges for motor operations.
Suggest to wire the windlass to the starter FLA, the FLA in best case should then be a hybrid starter/house type for eg cooling trucks. this because a windlass can run for longer time eg 60m chain out and eg anker gets stuck.
if you do that a MRBF fuse is ok for that LFP, inner resistance or this is higher and 10000A therefor enough.

[LifesBetterWhenYoureBeating]

Originally Posted by CaptainRivet

highly recommend not to use this for the windlass.
1200W is 140A cont and peaks to 500A. your battery can do short-term at best 400A. the 200A cut off is realized by mosfets which get easily blown by surge and reverse current that a motor can create. then the whole battery is dead. You have a house LFP with quite low spec cells. that's made for low continues C rates but not high surges for motor operations.
Suggest to wire the windlass to the starter FLA, the FLA in best case should then be a hybrid starter/house type for eg cooling trucks. this because a windlass can run for longer time eg 60m chain out and eg anker gets stuck.
if you do that a MRBF fuse is ok for that LFP, inner resistance or this is higher and 10000A therefor enough.

Thanks a lot for the explanation! I was already considering expanding my starter bank to have it as a backup in case the lithium misbehaves, so now I'll definitely do that and use it to power the windlass. I'm just not sure what you mean by starter FLA and mixed starter/house type.

[CarlF]

The windlass and starter electric motors are very similar. They draw lots of current for brief periods. Since the load is brief, you don't need a "deep cycle" battery as a start battery. You want a lot of amps - what is referred to as CCA (cold cranking amps) on AGM and FLA starting batteries labels.

Here is a good piece on some of the issues you are facing while upgrading to Lithium. It would be best to have a marine electrician familiar with lithium batteries on boats help you. It's very easy to get this wrong and damage your batteries, alternator, electrical system, or even start a fire.

https://marinehowto.com/drop-in-life...ated-consumer/

[boatpoker]

Originally Posted by gsalgado

Thanks a lot for the explanation! I was already considering expanding my starter bank to have it as a backup in case the lithium misbehaves, so now I'll definitely do that and use it to power the windlass. I'm just not sure what you mean by starter FLA and mixed starter/house type.

Is your alternator capable of charging the lithiums ?

Is your charger capable of charging the lithiums ?

[CaptainRivet]

Originally Posted by gsalgado

Thanks a lot for the explanation! I was already considering expanding my starter bank to have it as a backup in case the lithium misbehaves, so now I'll definitely do that and use it to power the windlass. I'm just not sure what you mean by starter FLA and mixed starter/house type.

pure starter FLA batteries have very thin lead plates to create short term high current, the so called CCA=cold cracking amp. a starter on engine is used for 30sek maybe a 1min max. a pure lead starter you can use 20% of its capacity maximum.
A windlass is used for 3-20min depending how much chain you have put, weather condition and if it got stuck. but needs CCA too but not that much as a starter is typical 2kw while windlass half of it.
so a windlass needs half CCA but need to deliver longer current. A hybrid lead starter and house battery is best for that but they are quite expensive. A cheap very good alternative are commercial grade starter batteries for cooling trucks. they have thicker lead plates and can be discharged to 40% but still have 80% of the CCA of a pure starter FLA battery.
this you can use as starter and as emergency house.
as it's CCA is 20% lower you just get the next size up from your current FLA starter eg you have now 88AH then you take the 100AH. gives you the advantage of double capacity 40AH instead 16AH to use and to start your engine and operate your windlass from it and act as emergency house.
I have very good experience with the Fiamm power cube EHD. have 2x 100AH of them as my starter +emergency house on my cat. I have 816 AH LifePo4 and a not current carrying BMS, so I can easily run my 1000W windlass of the LFP house.
And I had 4 of the fiamm in 140AH as house+bowtruster bank i' my former long keeler 12m ketch with a 18m bowtruster that sucked 800A out of these for 6 years.

[goboatingnow]

A windless will eat through a cheap SLA starter battery in no time.

Nor does it make any sense to build redundancy to protect you from Li failure. That’s madness. The Li bank will be extremely reliable better then any other battery on board. If you don’t trust thd tech why Fit it.

Lithium is way way better at high current provision then any cheap SLA . Look at all those Lithium jump start packs etc.

The issue is a crappy mosfet based BMS

I design with mosfet every week I would have a Li mosfet disconnect unless it’s was 400v 600A rated. This is possible with modern mosfets , but it’s expensive.

A far better choice is a high power relay disconnect not mosfets.

If you have 2C Li capable batteries and 300Ah , you have 600A at your disposal and short spike current way above that. Clearly if you have cheaper 0.5C Li , you have 150 A

I have 1000W 12 tigres windlass , I put my fluke 43B fluke meter on it to review the current consumption. ( as I was designed an e-fuse for it )

Full locked rotor amps was around 100A , operating currents were well less. Mine is setup to slip , instead of locked rotor

The whole “ drop in “ Li market is an abomination in my opinion firstly it’s not ABYC/ISO compliant. Secondly it facilitates cheap battery orientated BMS rather then bank orientated

Li on a boat is a complete system overall it needs to be approached that way.

[LifesBetterWhenYoureBeating]

Originally Posted by CaptainRivet

pure starter FLA batteries have very thin lead plates to create short term high current, the so called CCA=cold cracking amp. a starter on engine is used for 30sek maybe a 1min max. a pure lead starter you can use 20% of its capacity maximum.
A windlass is used for 3-20min depending how much chain you have put, weather condition and if it got stuck. but needs CCA too but not that much as a starter is typical 2kw while windlass half of it.
so a windlass needs half CCA but need to deliver longer current. A hybrid lead starter and house battery is best for that but they are quite expensive. A cheap very good alternative are commercial grade starter batteries for cooling trucks. they have thicker lead plates and can be discharged to 40% but still have 80% of the CCA of a pure starter FLA battery.
this you can use as starter and as emergency house.
as it's CCA is 20% lower you just get the next size up from your current FLA starter eg you have now 88AH then you take the 100AH. gives you the advantage of double capacity 40AH instead 16AH to use and to start your engine and operate your windlass from it and act as emergency house.
I have very good experience with the Fiamm power cube EHD. have 2x 100AH of them as my starter +emergency house on my cat. I have 816 AH LifePo4 and a not current carrying BMS, so I can easily run my 1000W windlass of the LFP house.
And I had 4 of the fiamm in 140AH as house+bowtruster bank i' my former long keeler 12m ketch with a 18m bowtruster that sucked 800A out of these for 6 years.

Unfortunately I'd have to import those fiamm and that'd cost more than the actual batteries.

My starter battery is 100Ah with 900CCA, 1y old, and my Perkins 4.108 always starts in literally a couple seconds, plus the battery resting voltage is 12.8v, so I believe it's in very good shape. My plan is to add another battery to my starter bank so that I can be sure the windlass won't kill them (even though I believe that'd be unlikely as I only ever run the windlass with the engine on and I have a high output balmar alternator). The problem is I won't be able to get a battery identical to my existing one here, so I'm wondering if I should try to get something with the same specs or a commercial grade starter battery as you suggested?

[LifesBetterWhenYoureBeating]

Originally Posted by boatpoker

Is your alternator capable of charging the lithiums ?

Is your charger capable of charging the lithiums ?

My LFP is currently only charged by solar/wind and those can. I'm also going to install a 30A dc2dc charger to charge then via the starter bank

[Jammer]

Originally Posted by gsalgado

Hi folks,

I've recently learned that I need over current protection on the wire going from my house bank to my switch, and since that bank powers my windlass, watermaker and other house loads, I'd need at least a 200A fuse to avoid nuisance tripping. However, I've just switched my bank to a single 300ah LifePO4 with a BMS that limits continuous discharge to 200A, so I'm wondering if it'd be ok to rely on that to protect the wire from the battery to the switch?

Well, what is "ok?"


I had a short at the starter solenoid once on a skid loader. There was a lot of smoke, and I ended up buying a new battery and a new battery cable. Skid loaders being made more or less entirely of steel, there wasn't much to burn.

On my last sailboat I installed MRBFs for the batteries and the starter and I have them on the battery for my 12' aluminum dinghy. They're compact, inexpensive, readily available, and reliable.

You decide for yourself.

[CarlF]

Originally Posted by gsalgado

My starter battery is 100Ah with 900CCA, 1y old,

I'd first try with the one battery and running the engine when using the windlass. I bet it will work fine. Windlasses only draw a lot of amps when breaking out an anchor - assuming you don't use the windlass to pull the boat to the anchor. The high load is only a few seconds like a starter. A bow thruster is a much bigger problem since it draws lots of amps whenever it's on.

Your high output alternator should handle most of the load. This will also push the voltage up above 13v so the windlass will run better.

Do calculate the voltage drop of the cables going to the windlass. Keep the voltage drop at 5% or less. This may require pretty big cables but it's worth it.

[fxykty]

Regarding windlass current draw, it must depend on the windlass. What are its specifications? We have a Lofrans Falkon windlass with 12V 1700W. It is protected by a 125A breaker. AFAIK there are no huge current draws during operation - otherwise the breaker would open.

Back to the OP, as others have said, don’t rely on the BMS and fuse the battery. Fuse or breaker the supply wire to the windlass with whatever size protection the windlass specifies. Hopefully that’s within the operating profile of your battery. It’s not rocket science.

[wholybee]

I know if several boats with cheap 100A Daly BMSs running their windlass. While the Internet forums are full of posts saying it won't work, in fact, it does work quite well. (I'm not endorsing a cheap 100A BMS, but relating real world experience.)

100A is the continuous current rating. The BMS will handle much more than that intermittently. The overcurrent cutoff on a cheap non-programmable daly 100A rated BMS is 360A. A 1000W windlass will draw 1000W (76A) at it's max pull. It will exceed that current if it stalls. Max pull (I am referencing a lofrans windlass) is 575kg, or 1267lbs. I can pull an anchor and chain up by hand, which means the load is going to be under 200lbs. So, for continuous use, the motor is lightly loaded, and less than 76A. If it stalls, a 100A circuit breaker will trip. On startup, there is usually no load, so startup currently isn't super high.

Don't use the windlass to pull the boat to the anchor, and don't use the windlass to break the anchor free. That's the rule even with SLA.

[goboatingnow]

Originally Posted by wholybee

I know if several boats with cheap 100A Daly BMSs running their windlass. While the Internet forums are full of posts saying it won't work, in fact, it does work quite well. (I'm not endorsing a cheap 100A BMS, but relating real world experience.)



100A is the continuous current rating. The BMS will handle much more than that intermittently. The overcurrent cutoff on a cheap non-programmable daly 100A rated BMS is 360A. A 1000W windlass will draw 1000W (76A) at it's max pull. It will exceed that current if it stalls. Max pull (I am referencing a lofrans windlass) is 575kg, or 1267lbs. I can pull an anchor and chain up by hand, which means the load is going to be under 200lbs. So, for continuous use, the motor is lightly loaded, and less than 76A. If it stalls, a 100A circuit breaker will trip. On startup, there is usually no load, so startup currently isn't super high.



Don't use the windlass to pull the boat to the anchor, and don't use the windlass to break the anchor free. That's the rule even with SLA.

My windlass in calm conditions happily pulls me to the anchor and happily pulls it out.

The fact that there are lots of boats with poor systems but working is irelevant. The point is what the SHTF , it will fail

[mcon12000]

Originally Posted by wingssail

CharlieJ, Your post should be modified thusly:

Every single B+ conductor on a boat, with the exception of the conductor supplying engine starters, to meet ABYC standards and to be safe from fire and electrical shorts, must be protected with an appropriately sized overcurrent protection device (OCPD), i.e., fuse or circuit breaker.

Many of us with older boats which never had fuses on all conductors, for example from the batteries to the battery switch, or from the battery switch to the distribution panel, or from the alternator to the battery switch, have elected to live with that, and we rely on breakers on the panel for every attached device, so "must" seems a bit presumptuous. It's not something I "must" have. Maybe "should" but not "must".

The OP has now modified/upgraded the “Old System” so I can assure you it needs to meet ABYC standards now. I understand your point of view with an untouched system but adding lithium, an inverter, solar blah blah creates a need for compliance.

We’re not far off from electrical audits if you need shore power in a marina.

[mcon12000]

These conversations about the BMS’s ability to handle the windlass could possibly confuse some people.

The “breaker” specified by the manufacturer of one’s windlass is there to protect the windlass.

The fuse that must be on the windlass circuit is to keep a dead short from destroying your boat.

In a proper windlass circuit you’ll have a “Fuse” and a “Breaker” … Both not one or the other.