LFP/Solar chat - deals, design, Q&A, etc

[Barking Sands]

Don't make me call the ABYC police on you people!

 

[Datenight]

Yeah, that's what I did. I have 250A fuses on each batt and a 400 on the main line. I'm not worried.

That’s what I did, 250 amp class T on each battery and 400 on the main.

Rob

 

[luna]

My understanding is the new E-11 requires individual battery protection, and for the whole bank. 900AH of LFP (if we ignore the fact that they already have short circuit protection) will require 45K AIC. A class T doesn't do that at 125V, but does it do that at 12V? ABYC needs to contemplate the real world, not just a fantasy one. The fuses I'm finding with that sort of spec are in the $500 range. And you aren't going to find a replacement in a rural port.

Since the batteries are spec'd and even tested for short circuit protection, I may just ignore all this as being unrealistic.

It's not quite that bad, but I agree that ABCY seems to live in a different world than us mere mortals.

Mersen offers an A3T Series of fuses that are fast acting, compact, has a 50kA IR value (at their 160 V rating?) and although you won't find them at you local chandlery they are commonly available and not materially different in price compared to the standard JLLN offering from Blue Seas etc.

A3T400

A3T400 Mersen 400A 300 Vac, 160 Vdc Ferraz Shawmut is Mersen. Mersen A3T fast-acting fuses combine two highly desirable features - high current-limitation and a small physical size. Their unique dimensions prevent the substitution of other fuses with lower voltage ratings or current-limiting...

witonics.com

I think the A3T fuses will fit into a Blue Seas Class T fuse holder. If so, that is a good thing as Mersen seems to only offer fuse holders that use direct bearing box connectors which ABYC prohibits. Mersen's design is understandable because the market for these kind of components does not use type 3 stranded wire.

Maybe the committee at ABYC should provide some guidance on how to achieve compliance.

 

[DDW]

I don't think those are going to fit in a standard Blueseas fuse holder. For one thing the holes are larger, and the spacing varies by amp rating as does overall length. Might be able to get one particular size to fit.

But this is exactly the point. Recommendations with no practical means of compliance are meaningless. Having to do a deep search of the internet and cobble together a home made fuse holder is not practical.

There should also be some consideration for the frequency of the contemplated disaster: How many boats have burned to the waterline due to a shorted battery which fused an ordinary class T fuse? Has there even been one? On the other hand I can see all sorts of problems with the many extra cables and connections required.

 

[Marco Flamingo]

I looked into class T fuses for my LFP install. Then I understood why my PO had figured out a way to cobble together class T fuses without using holders. The holders cost as much or more than the single-use fuse, and class T fuses are already overpriced for what they do. I figured out a DIY way to cover up the class T fuses and I still use them downstream of my breakers.

I posted a good YouTube video here (that I can't find now) showing how a MCCB thermo-electric breaker works. Very interesting video. It shows the rare earth magnets that draw any arcing into a metal-finned chamber that snuffs the arc. It has an electro-magnet coil that trips the breaker instantly on high current. Also a bi-metallic strip that trips on lengthy but lower overcurrent. MCCBs are available up to 100kA AIC. It is easy to see if they have tripped, and they can be reset once the problem is fixed. Keeping class T is like keeping lead batteries. Great technology in its day, but harder and harder to justify.

I also went through the process of trying to decide how many cables and connections to use. Because my LFP batteries are connected directly to my alternator, each BMS gives me another layer of protection from some type of overcurrent shutdown. I went with 4 LFP, but thought about 6 or 8 smaller batteries. The likelihood of 8 LFP BMSs shutting down simultaneously is way less than 4 shutting down all at once, but I would have at least 16 more connections. What is more likely to cause a problem, BMS/alternator issues that gets past my alternator protection module, or more complex and numerous connections and cables? Not sure how to do this risk analysis and wanted to avoid being (bad) redundant.

 

[luna]

I don't think those are going to fit in a standard Blueseas fuse holder. For one thing the holes are larger, and the spacing varies by amp rating as does overall length. Might be able to get one particular size to fit.

But this is exactly the point. Recommendations with no practical means of compliance are meaningless. Having to do a deep search of the internet and cobble together a home made fuse holder is not practical.

There should also be some consideration for the frequency of the contemplated disaster: How many boats have burned to the waterline due to a shorted battery which fused an ordinary class T fuse? Has there even been one? On the other hand I can see all sorts of problems with the many extra cables and connections required.

I don't think that I am looking at the wrong fuses when I compare the sizes of Mersen's A3T in 200 to 400 A and Blue Seas (really Littelfuse ) Class T in 225 to 400 A offerings.

All of the dimensions shown on the dimension drawings for these 2 manufacturers are identical except the barrel of the Mersen is 0.020" longer and the holes in the Blues Seas fuse is shown to accept a 10mm (0.393") bolt, while Mersen says theirs is 0.41" in diameter. It appears to me that neither of these differences would stop you putting a A3T-400 fuse in a Blue Seas fuse holder. I also doubt that there is anything materially wrong with doing exactly that.

I have no stats on the frequency of the contemplated disaster, but I would hope that ABYC has research that justifies their positions. Perhaps someone here knows the genesis of this requirement.

Once you cross the 50kA threshold by having a LFP bank larger than 1000Ah, I think you will be cobbling something together as most if not all of this size of fuse holder uses barrel connectors unless you opt for a modular style of fuse block and the appropriate enclosure.

 

[DDW]

A 400A will blow rather quickly I think driving a 6.3kw thruster. The Sidepower recommendation is a 500A ANL, but of course it does not have 50k AIC rating. The 500A AT3 might be modified to fit, but the Bluesea holder is only rated to 400A. And the quick blowing nature of the AT3 might cause nuisance blows unless we go all the way to the Sidepower nominal 740A draw. Then we need to find a holder, and decide if an 800A fuse is appropriate for 3/0 or 4/0 cable.

It is a quagmire. And to solve what problem? The manufacturer claims that the BMS will shut down in 500µS at 800A. Is my cobbled together solution of a hard to find fuse and home made holder thought to be more reliable? How much of a fire would 30,000A through a 4/0 cable start? My guess is it would burn through more or less instantly. One of the imagined hazards is a shorted cell getting a bunch of power dumped to it - but fusing individual batteries or the whole bank does little to mitigate that risk, which is present within a single packaged battery.

Let's say I have a 14' run of 3/0 to a thruster. That is 0.002 ohms. Applying a 13V unlimited current voltage source will not result in 50KA if the ends are shorted, but only 6600A. Of course one cannot plan to have the short at the ends, but this raises the question: Would it not be better to put the money and effort into cleaning up cable runs a little so they are unlikely to short? To get the imagined 50KA would really require dropping a very heavy copper bus bar directly across the battery terminals. Your fuse won't do you any good there, unless it is inside, or perhaps an MRBF.

So from a 10,000 foot level, we have hazards that may exist in theory but are certainly not commonplace, solved by unobtanium hardware, with known and unknown negative consequences. I'd like to hear the arguments for why it was thought reasonable to recommend this, along with the accident statistics justifying it. And suggestions of how to comply.

I'll postulate that an MRBF fuse on each battery is probably safer (from real world hazards) than a bunch of cables, connections, and cobbled together fuses and holders with a 50K AIC rating, each of which is a potential source of failure resulting in created hazards.

 

[rslifkin]

On top of the BMS cutoff, some batteries (like my Epoch V2s) have an internal fuse as an additional safety. It's not of known specs like a Class T and is likely over-sized for the wiring, so not helpful for ABYC compliance, but in the event of a dead short that would potentially arc an MRBF or Class T, it's likely going to blow if the BMS fails to shut down in time.

Basically, I'm with DDW on this one. The ABYC recommendations here seem to be somewhere between reasonable / effective risk mitigations and what we could probably think of as "unicorn insurance".

 

[SteveK]

The size of the fuse determines the holder. Up until now up to 400A was enough. Would not be surprised if blue seas comes copies with this one

 

[DDW]

Looks like the BEP 600A version would fit a 600A A3T.

 

[Barking Sands]

On top of the BMS cutoff, some batteries (like my Epoch V2s) have an internal fuse as an additional safety. It's not of known specs like a Class T and is likely over-sized for the wiring, so not helpful for ABYC compliance, but in the event of a dead short that would potentially arc an MRBF or Class T, it's likely going to blow if the BMS fails to shut down in time.

Basically, I'm with DDW on this one. The ABYC recommendations here seem to be somewhere between reasonable / effective risk mitigations and what we could probably think of as "unicorn insurance".

I agree. I have the V2s with its fancy internal fuse. From there I have just put MRBF fuses for the wire.

I can tell you we have done some very tough testing of the V2 and V2-T with the fancy fuse. During an abuse session of a prototype we had a fuse blow. It appears that fuse not only has the 400amp thermal capability but that fuse can be blown by the BMS in a failsafe manner. BMS fails>blow the fuse. I am pretty confidant in the V2 for its safety. Just wish I could get the specs...lol.

 

[luna]

Looks like the BEP 600A version would fit a 600A A3T.

That seems to be what BEP says.
So we have gone from an expensive ($500) fuse, past the quagmire and on to the A3T 600 at $260 and the BEP fuse block at $75.

I think you will have other challenges safely getting 500 amps from the batteries through the conductors to the thruster motor.
Perhaps a new 24 V thruster motor is in your future.

 

[DDW]

Actually the amps have been getting through the conductors to the thruster motor for 12 years now without incident. Not just on my boat but on 27 sister ships built the same, and countless others following the Sidepower's installation instructions.

I've yet to be convinced that spending the ~$600 (fuse, spare fuse, fuse block) will result in any increase in safety. What I'd like to see is some testing on direct shorts in real circuits with real batteries showing how the fuse does anything for me at all beyond the many fuses already there.

 

[DDW]

Actually the Mersen fuse it quite a bit cheaper than that. It starts getting practical at that price.

 

[luna]

Good to see that the costs can be reduced by thorough shopping. I just picked the first guy up on my search as I needed to go get dinner ready.

I as well would like to see a justification for the mental, physical and economical gymnastics that ABYC seems to enjoy putting us all through. Although I won't hold my breath waiting for that to happen.

 

[Bmarler]

Maybe they make the standard to force the production of new devices.

 

[DDW]

Still there ought to be reasons for the standard. I ask again for a single instance of a T class fuse arcing closed from a dead short on a boat, resulting in the loss (or significant damage) of the vessel. And statistics justifying the expense and loss of reliability for every vessel.

 

[slowgoesit]

Still there ought to be reasons for the standard. I ask again for a single instance of a T class fuse arcing closed from a dead short on a boat, resulting in the loss (or significant damage) of the vessel. And statistics justifying the expense and loss of reliability for every vessel.

Oh, come one, stop trying to figure out if the standards (actually recommendations) have any basis in reality, just bite the bullet and pay some "professional" to make his best guess at how to comply with a really confusing "standard".

 

[luna]

Oh, come one, stop trying to figure out if the standards (actually recommendations) have any basis in reality, just bite the bullet and pay some "professional" to make his best guess at how to comply with a really confusing "standard".

I have read more than once on this site that ABYC produces recommendations not standards.

But a recommendation is not what ABYC actually calls their product. They call it a voluntary global safety standard.

This is directly from their site:
"The American Boat &Yacht Council (ABYC) is a non-profit, member organization that develops voluntary global safety standards for the design, construction, maintenance and repair of recreational boats."
I had a quick look through their site and did not find the work recommendation anywhere.

Voluntary many would suggest would mean that you have a choice on adopting this standard. That notion vanishes once the Surveyor and Insurer are through with you.

Let's just call it what it is.

 

[Serene]

I have read more than once on this site that ABYC produces recommendations not standards.

But a recommendation is not what ABYC actually calls their product. They call it a voluntary global safety standard.

[SNIP]

"Global"

Are they delusional?

Nobody in Australia even knows what ABYC is, as we have our own Australian and New Zealand standards for marine electrical installations AS/NZS3004.2

 

[luna]

I don't think it is fair to state that "Nobody in Australia even knows what ABYC is"

Among other members scattered about, there are about 15 Members of the club in Italy, 8 in China/Taiwan, 12 in Australia and 8 in New Zealand.

Here is their Membership Directory, have a look.

Member Directory - The American Boat & Yacht Council

abycinc.org

One would think it is likely that someone from outside of the US would be on one or more of the various Standards Commitees.

That being said, I still think that they have some splainin to do.

 

[BruceK]

I don't think it is fair to state that "Nobody in Australia even knows what ABYC is"

Among other members scattered about, there are about 15 Members of the club in Italy, 8 in China/Taiwan, 12 in Australia and 8 in New Zealand.

Here is their Membership Directory, have a look.

Member Directory - The American Boat & Yacht Council

abycinc.org

One would think it is likely that someone from outside of the US would be on one or more of the various Standards Commitees.

That being said, I still think that they have some splainin to do.

Pedants Unite!
Aussie TF members, all 12 of us, (could have sworn it was more, how come we have 2 Moderators) likely only know of ABYC because of derogatory comments by US members. Long may it stay offshore.

 

[DDW]

Well, it is called the "American Boat & Yacht Council". Not "Australian" or "International" or "Global". Maybe their Mission Statement committee got a little overindulgent - many of them do.

 

[PNK]

This is really interesting to me, because I am considering a boat that has AGM batteries, with 2 X 175W solar panels, and a 5KW generator, and I would like to switch the batteries to Lithium. There is also a 3000W inverter and a Xantrex charging monitor.
Can these simply be swapped, or is the change more involved? ( I am guessing that it is.)
Given how much the price of these batteries has come down this seems like a good time to get it done.
The AGM batteries are new, or new-ish, and I am not sure how the longer life of lithium would compare.
Thanks for the help!
Peter

 

[DDW]

Provided the solar charge controller and charger/inverter can be set to lithium voltage ranges, they would not need to be changed. I'd caution three things: buy batteries that have a BLE connected BMS, preferably one that allows access from the Overkill app, and make sure they do not have Full Charge Protection as a feature. I would refuse anything else. That may eliminate the cheapest options, but there are still plenty of options.

Second, plan your install to make sure there is protection against a battery disconnect which can fry your alternator and all kinds of other things. There are more than a few ways to do this, the easiest and safest are to charge the lithium batteries through a DC-DC charger, or keep at least one AGM battery in the charging system. You will need to educate yourself a little on this.

One last concern is a stock alternator may run very hot charging the lithium, the DC-DC scheme mentioned above can mitigate this, or you may need to go to an externally regulated alternator which can control the alternator temperature.

 

[Marco Flamingo]

Here is that video that shows how an MCCB works. The venerable Class T is a fuse inside of a chamber filled with dirt (actually, sand). When the fuse blows, the dirt gets in the way and can stop an arc of less than 20kA. The MCCB is way more sophisticated for less $$. In searching for this video, I noted that there are a lot more videos on MCCB than when I first researched.

Can these simply be swapped, or is the change more involved? ( I am guessing that it is.)

I swapped with probably the least complexity. The thread is Going from lead to lithium. My change over wasn't difficult or expensive because I already had 1) an external alternator regulator and 2) room for four largish LFP batteries with Bluetooth. I had plenty of room because I removed my generator. I didn't need to choke down the alternator output with DC/DC or keep lead in the charging system. Instead, spend that money on more LFP.

 

[Bmarler]

This is really interesting to me, because I am considering a boat that has AGM batteries, with 2 X 175W solar panels, and a 5KW generator, and I would like to switch the batteries to Lithium. There is also a 3000W inverter and a Xantrex charging monitor.
Can these simply be swapped, or is the change more involved? ( I am guessing that it is.)
Given how much the price of these batteries has come down this seems like a good time to get it done.
The AGM batteries are new, or new-ish, and I am not sure how the longer life of lithium would compare.
Thanks for the help!
Peter

If the agms are newer, I would wait a year or two. There are always needs on a new to you boat, so if something is already addressed, let it ride.
I put all new agms in before lithiums started getting affordable. I’ll run them as long as possible before I do the switch.