Trojan lithium drop in replacement

[rgleason]

Yes, John, provided our own separate charge and discharge cutoffs/relays are set right it would not matter, but I would want to make the battery LVD and HVD settings a little more conservative. That involves the BMS.

Originally Posted by john61ct

Will be Trojan's design I'm sure not available separately.

And I'd be amazed if setpoints were user-adjustable, BMS does not often control the charging sources, just last-layer battery protection for when user-level gear fails.

But the CAN-bus comms may allow for some flexibility, each pack under the control of a rPi or Arduino "master control unit" for example rather than adding traditional mechanical relay/contactor controls outside.

[john61ct]

I have yet to see any BMS with adjustable setpoints.

Yet another reason to roll your own if so inclined.

Note with most BMS, they do not start doing any cell-level balancing until voltage is at a higher point than I would want to see on a bank in daily usage.

But keeping voltage low like that means that functionality is not needed, or at least easily done as periodic manual maintenance.

[Davidhoy]

Originally Posted by rgleason

Yes, John, provided our own separate charge and discharge cutoffs/relays are set right it would not matter, but I would want to make the battery LVD and HVD settings a little more conservative. That involves the BMS.

Why would you add the complexity of your own low- and high-voltage cutoffs when the battery already manages that for you? That's the point of an integrated battery, it has the contactors and intelligence built into the pack itself. And if you say you don't trust that Trojan got it right, then don't buy their battery, and roll your own system from scratch. I'd actually argue that the integrated approach adds redundancy, as each battery is managed individually - if one goes bad, just disconnect it from the bank and you're good to go on the remaining packs.

-David

[john61ct]

The idea being, for very large and / or mission-critical use cases, defense in depth.

The vendor BMS LVD/HVD is reserved for last-ditch failsafe use, only triggered when the "user-level" controls suffer a failure.

For 4S systems, in daily use my zero SoC is 11.99V and my 100% cutoff is 13.81V.

As long as everything works as it should, the BMS protections are a redundant layer, as IMO is proper.

[Davidhoy]

Originally Posted by john61ct

The idea being, for very large and / or mission-critical use cases, defense in depth.

The vendor BMS LVD/HVD is reserved for last-ditch failsafe use, only triggered when the "user-level" controls suffer a failure.

For 4S systems, in daily use my zero SoC is 11.99V and my 100% cutoff is 13.81V.

As long as everything works as it should, the BMS protections are a redundant layer, as IMO is proper.

Not sure I'd consider a house bank on a boat to be "very large" or "mission-critical". You're thinking about this from a traditional roll-your-own perspective. If you're building your own bank, then you definitely need appropriate LVD and HVD contactors, but duplicating the functionality already included in each individual battery seems like you're introducing additional points of failure.

These new Trojan batteries need some positive reviews (and I suspect Maine Sail will give them a very thorough review) before anyone starts using them in their boat. Then we will know...

[ontherocks83]

Originally Posted by Davidhoy

These new Trojan batteries need some positive reviews (and I suspect Maine Sail will give them a very thorough review) before anyone starts using them in their boat. Then we will know...

I think I will trust Maine Sails' opinion/optimism/future reviews over certain other opinions

[john61ct]

Originally Posted by Davidhoy

Not sure I'd consider a house bank on a boat to be "very large" or "mission-critical"

Of course not in most cases.

I was discussing the needs of those that are, answering the question "why would you".

And yes, nothing to do with any specific batteries.

Some people believe the BMS should actually be involved in daily usage, you run them down and charge them up until it cuts you off.

That will of course result in a lifetime that is a small fraction of their potential cycles, and IMO at the prices charged a tragic waste.

[senormechanico]

john61ct answer about hitting the BMS limits reminded me of my father in law's way of parallel parking his car.
He'd back up or go forward until he heard something ( hitting the ones ahead or behind his ).


I really gave it to him when he smacked mine and he said, "Isn't that what bumpers are for?

[john61ct]

Great analogy there, I just might borrow that 8-)

[rgleason]

Good point about balamcing but I ve found several with adjustible HVD and LVD.

[john61ct]

Maybe start a new "currently available BMSs for LFP" thread with links, notating the adjustable ones?

If you think worth doing anyway, IMO would be a useful reference for those interested.

[rgleason]

I started one. Will find it.

[rom]

13.6 kg for 110 Ah makes about 122 kg for a 1000 Ah, where it would be around 150 kg using Winstons. Sounds good ! Hopefully the price will be "competitive" against Winston, not Victron.

[tanglewood]

I think the success or failure of all these "drop-in" batteries lies in the diligence paid to the fine print in the manuals, and the ensuing adjustments and refit as needed to all the charging sources. I see it as no more or less work that installing any other system, since most of the work and skill is still in evaluating the rest of the power system and bringing it into compliance with good LFP practices.


The poison is that the "drop-in" moniker will lead people to buy first, and read the fine print later, and we know how much time people spend reading fine print. I expect most buyers will assume no action is required WRT the rest of their power system, and off they will go.


I fear it will all end badly 3 to 5 years from now, and give LFP a really bad name.

[john61ct]

Just meeting the vendor spec'd cycle lifetimes will exceed most expectations,

conditioned to be very low by lead.

Most will be completely unaware they could get much longer by that extra effort.

Lots of owners don't even keep their boat for much over five years.

And normal (poor) people won't be buying them anyway.