Making a cheap BMS ABYC compliant

[goboatingnow]

Originally Posted by rgleason

Some very interesting ideas here.

What about using goboatingnow's earlier idea for 3 smaller lfp 100a (rated at 100a continuous charging) each with a mosfet bms like daly, wired in parallel which provides enough diversity, in the event of one of the batteries being shutdown, to protect the alternator from spikes?

Throw a small FLA and a Balmar spike protector in the system for a little more peace of mind .. use of the FLA and the fact that there is no advance alarm, excludes this from ABYC compliance. However the bms could also use jedi idea for an advance disconnect of the alt/regulator


Goboatingnow wrote:

In other words connect a suitable dc dc from the alternator directly to the lfp , instead of modifying the alternator...

Another interesting idea. Would this really work?

I know it works cause I’ve used it. The alternator has no issues powering that dc dc direct. It has a generous 60 v input range and I fit a TVS diode input protector to boot. Works good. Extra fan needed for high ambient cooling if mounted in a hot area

You can adjust CV and CC to ensure alternator isn’t stressed.

The key here is to stop accepting “ received “ ideas and look at this from a simple Dc engineering perspective.

Note that a certain spike occurs on major dc dc disconnect but the 60 v input range ability and a 18v TVS spike reducers cures this easily ( ie similar to Sterling APD device ) as the battery is not on the alternator circuit the spike does not propagate beyond the dc dc unit and the alternator. The nature of the dc dc input circuit is a certain load remains anyway and helps spike reduction

Sterling themselves use the same concept as a alternator regulator

That’s no requirement to have any battery in the alternator circuit and good reasons these days not to have it.

[goboatingnow]

Again there is no requirement to have any battery in circuit with a modern alternator. The regulator will be happy with any dc load.

[s/v Jedi]

Originally Posted by rgleason

Some very interesting ideas here.

What about using goboatingnow's earlier idea for 3 smaller lfp 100a (rated at 100a continuous charging) each with a mosfet bms like daly, wired in parallel which provides enough diversity, in the event of one of the batteries being shutdown, to protect the alternator from spikes?

Throw a small FLA and a Balmar spike protector in the system for a little more peace of mind .. use of the FLA and the fact that there is no advance alarm, excludes this from ABYC compliance. However the bms could also use jedi idea for an advance disconnect of the alt/regulator


Goboatingnow wrote:

In other words connect a suitable dc dc from the alternator directly to the lfp , instead of modifying the alternator...

Another interesting idea. Would this really work?

The problem is that unless a cell is defect, a HVC only occurs at high SOC and when one battery disconnects, you can expect the others to follow rapidly, like a chain reaction.

You can mitigate that by not fully charging from the alternator; for a 12V system, you could set the regulator to 13.6V, so 3.4V per cell, which means something must be really wrong before HVC occurs.

That said, it is so simple to use the MOSFET’s from the BMS to signal HVC/LVC, use that to turn off the regulator and one second later disconnect the battery using an external contactor, RBS etc.

There is yet another way if you have access to the cells: use midpoint monitoring with a Victron BMV, or use a $10 cell monitor and set the alarm lower than the BMS HVC value and use the alarm output (or make one from its beeper) to disable the alternator regulator.

I’m on PCB design again, bringing a new BMS PCB higher up my list. With that, you just buy cells and slap a BMS on that can do it all for a couple dollars… even make it do whatever you want using simple Arduino sketch.

[goboatingnow]

I fully agree nick , HVC mitigation is very easily accomplished and likely to be extremely rare anyway . I’d happily take the alternator rather risk as it most likely HVC occurs when the alternator is not tremendous load , if you get a sudden full load HVC disconnect , something seriously has gone wrong and potentially blowing up the alternator may be the least of the worries.

As yiu say it’s fairly trivial to build in alternator disconnect signalling

My point was that there are several ways to directly couple ones alternator directly to a LFP bank bypassing the lead starter. Some solutions are quite cheap n fact the 30A dc dc unit I referred too is virtually disposable but in fact has been surprisingly robust.

Hence several ways to skin cats.

[rgleason]

Thanks gbn and jedi. So due to the HVE cascade, it would be simpler to just build one lfp battery 200-300ah with the alt/regulator advanced disconnect using Daly BMS, and perhaps limit charging voltage to 13.6v. Then I'd get full use of 100a charging from the alt.

[s/v Jedi]

Originally Posted by rgleason

Thanks gbn and jedi. So due to the HVE cascade, it would be simpler to just build one lfp battery 200-300ah with the alt/regulator advanced disconnect using Daly BMS, and perhaps limit charging voltage to 13.6v. Then I'd get full use of 100a charging from the alt.

I’m not sure what you want: better, cheaper or simpler. I guess you’re trying to find a middle way of compromise.

Going for one battery for the sake of simplicity is a step too far and a decision made on wrong factors. You need to start deciding on which cells. As we can expect the cost factor to play a role, you have to accept more balancing issues than with high end cells like Winston. Let’s say you get Eve 280Ah cells.

With the cells decided, you now have to decide on voltage and related battery capacity. At 12V you get 4S so 4 x 280Ah x 3.2V = 3.6kWh. This is good for a boat with propane in a galley and two of these batteries.

For 24V you get 8S so capacity doubles to 7.2kWh. Two of those would be the bare minimum for a boat with electric galley. If you get a small, efficient, VSD based A/C you can run it in a cabin at night.

At 48V you get 16S and 14.4kWh which puts you well above the 10kWh that I feel very comfortable with, enabling using A/C in a cabin at night etc. But realize that all this capacity must be generated as well!

So let’s see at what solar arrays go with these: the dual 3.6kWh scenario needs 1kW solar, the dual 7.2kWh setup needs 2kW solar and the dual 14.4kWh needs a whopping 4kW solar. That last option is only possible for large catamarans.
A smaller solar array means running a genset or charging from the alternator.

The above scenario is based on still having redundancy and being able to temporarily do with just one of these batteries. In practice this means you look at what old batteries you have and you create one good bank at the new voltage you decide upon from the old batteries. Now you add a new LFP and start gaining experience. You will also need other gear, like probably new/extra solar, a big dc-dc converter if going from 12V to either 24- or 48V and a new inverter/charger as well.

I think people make a way too big deal from switching to a higher voltage. The dc-dc converter cost almost nothing and you can use a new inverter/charger anyway.

Enfin, now you run with that for a year or two and then replace the old batteries with the second LFP battery, which probably is gonna be from different cells and different capacity than the first, because you got wiser and new products came on the market. With those two LFP batteries you can run the full lifespan of the cells of the oldest battery. You don’t need to replace before they fail, because you have another, newer battery that can take you through the replacement period of the other battery.

So now you get to decide on the BMS, balancers etc. My recommendation: get a Daly BMS or one of the other similarly priced ones because they are cheap and they work. Set the alternator regulator to that lower 3.4V/cell absorption voltage and 3.3V/cell float voltage and go with it.

In the mean time, I will publish my DIY BMS that anyone can build.

[newhaul]

Originally Posted by s/v Jedi

I’m not sure what you want: better, cheaper or simpler. I guess you’re trying to find a middle way of compromise.

Going for one battery for the sake of simplicity is a step too far and a decision made on wrong factors. You need to start deciding on which cells. As we can expect the cost factor to play a role, you have to accept more balancing issues than with high end cells like Winston. Let’s say you get Eve 280Ah cells.

With the cells decided, you now have to decide on voltage and related battery capacity. At 12V you get 4S so 4 x 280Ah x 3.2V = 3.6kWh. This is good for a boat with propane in a galley and two of these batteries.

For 24V you get 8S so capacity doubles to 7.2kWh. Two of those would be the bare minimum for a boat with electric galley. If you get a small, efficient, VSD based A/C you can run it in a cabin at night.

At 48V you get 16S and 14.4kWh which puts you well above the 10kWh that I feel very comfortable with, enabling using A/C in a cabin at night etc. But realize that all this capacity must be generated as well!

So let’s see at what solar arrays go with these: the dual 3.6kWh scenario needs 1kW solar, the dual 7.2kWh setup needs 2kW solar and the dual 14.4kWh needs a whopping 4kW solar. That last option is only possible for large catamarans.
A smaller solar array means running a genset or charging from the alternator.

The above scenario is based on still having redundancy and being able to temporarily do with just one of these batteries. In practice this means you look at what old batteries you have and you create one good bank at the new voltage you decide upon from the old batteries. Now you add a new LFP and start gaining experience. You will also need other gear, like probably new/extra solar, a big dc-dc converter if going from 12V to either 24- or 48V and a new inverter/charger as well.

I think people make a way too big deal from switching to a higher voltage. The dc-dc converter cost almost nothing and you can use a new inverter/charger anyway.

Enfin, now you run with that for a year or two and then replace the old batteries with the second LFP battery, which probably is gonna be from different cells and different capacity than the first, because you got wiser and new products came on the market. With those two LFP batteries you can run the full lifespan of the cells of the oldest battery. You don’t need to replace before they fail, because you have another, newer battery that can take you through the replacement period of the other battery.

So now you get to decide on the BMS, balancers etc. My recommendation: get a Daly BMS or one of the other similarly priced ones because they are cheap and they work. Set the alternator regulator to that lower 3.4V/cell absorption voltage and 3.3V/cell float voltage and go with it.

In the mean time, I will publish my DIY BMS that anyone can build.

Ok now what size vessel and average ah draw are you building for?

I am happy with my current single battery 250ah 4p1s with 200amp single in and out Daly bms right now no alternator charging ( engine to be installed this winter) then will be adding a grp 24 fla and a 75 amp alternator and some type of dc dc from lead to lifepo4 . (Totaling in the 60 amp range) 200 watts solar through Tracer3210AN MPPT controller. All led lighting. Running anchor and domestic.
Remember not all of us are on big cats.
Am I missing something .?

Current 4x250x3.2v= 3.2kw. So I need 500 watts solar? Do fine with 200 so far.

[s/v Jedi]

Originally Posted by newhaul

Ok now what size vessel and average ah draw are you building for?

I am happy with my current single battery 250ah 4p1s with 200amp single in and out Daly bms right now no alternator charging ( engine to be installed this winter) then will be adding a grp 24 fla and a 75 amp alternator and some type of dc dc from lead to lifepo4 . (Totaling in the 60 amp range) 200 watts solar through Tracer3210AN MPPT controller. All led lighting. Running anchor and domestic.
Remember not all of us are on big cats.
Am I missing something .?

Current 4x250x3.2v= 3.2kw. So I need 500 watts solar? Do fine with 200 so far.

So you have a 12V 4S battery using 250Ah cells which comes to 3.2kWh (not kW, which is power instead of energy). With that setup you are a little under the 280Ah cells from my example, so you can’t run an electric galley. I’m sure you can use an induction cooktop now and then, but that’s not running a full time galley, which includes all meals, baking bread, making coffee and tea all day etc. You need at least a 5kW inverter for that as well.

Size of the boat doesn’t matter: you use the same cooktop, oven etc.

For the solar it matters of course. You have 200W solar so for a day you can only generate maybe one kWh? That’s less than a third of your battery capacity so it’s severely underpowered. If you don’t need another charge source, it means you don’t use that capacity and can even do with a smaller battery. Do you have refrigerator and freezer for full time provisioning? Entertainment systems, parties? Almost every boat can have two large solar panels on the stern for 800-1000W capacity. If Beau & Brandy can fit them, anyone can

[newhaul]

Originally Posted by s/v Jedi

So you have a 12V 4S battery using 250Ah cells which comes to 3.2kWh (not kW, which is power instead of energy). With that setup you are a little under the 280Ah cells from my example, so you can’t run an electric galley. I’m sure you can use an induction cooktop now and then, but that’s not running a full time galley, which includes all meals, baking bread, making coffee and tea all day etc. You need at least a 5kW inverter for that as well.

Size of the boat doesn’t matter: you use the same cooktop, oven etc.

For the solar it matters of course. You have 200W solar so for a day you can only generate maybe one kWh? That’s less than a third of your battery capacity so it’s severely underpowered. If you don’t need another charge source, it means you don’t use that capacity and can even do with a smaller battery. Do you have refrigerator and freezer for full time provisioning? Entertainment systems, parties? Almost every boat can have two large solar panels on the stern for 800-1000W capacity. If Beau & Brandy can fit them, anyone can

Primary is propane galley yes kW (auto fill ) I use about 30ah daily now . 2512 trace inverter charger. Technautics cool blue 3cf spill over fridge with 1.5cf freezer. R45 CRYOGEL insulation . All led. Use inverter in afternoons when bank is recharged to run my rice cooker. Occasionally use my newwave2 induction . I don't need an oven to bake bread. Mostly fry bread or tortillas. Occasionally watch a movie on my 24 inch TV mostly read books . Don't smoke or drink so no parties. Have z 3.2kw diesel yanmar genset to charge if I ever need it . May leave it behind have not needed it so far. And 800 watts is unthinkable on my 29 ft columbia defender. She's long and lean
A couple shots .
Now where do I place additional solar ? Without looking like a solar farm?
I am a flush deck so coach roof is out.

[s/v Jedi]

Beau and Brandy have a 1971 Pearson 35 so a little more space but they do electric drive as well!

The difference is the arch on the stern where they mount the big panels.

https://sailingsaoirse.com/about-us/

[newhaul]

Originally Posted by s/v Jedi

Beau and Brandy have a 1971 Pearson 35 so a little more space but they do electric drive as well!

The difference is the arch on the stern where they mount the big panels.

https://sailingsaoirse.com/about-us/

An arch like that would be nice problem for me is mainsheet is on end of boom and traveler is on stern just infront of the lazzerette. I am considering adding g my air 400 on the stern of this boat as well.

[s/v Jedi]

Originally Posted by newhaul

An arch like that would be nice problem for me is mainsheet is on end of boom and traveler is on stern just infront of the lazzerette. I am considering adding g my air 400 on the stern of this boat as well.

The picture you show above suggests that there is more than enough room for an arch behind the boom and traveler.

Where there is a will, there’s a way at least, this is a word for word translation from Dutch, I don’t even know if other languages have the same expression

[rgleason]

S/v Jedi.
You have my situation just about right. We use propane, have ozifridge, and autopilot and B&G radar. I was considering 280a of Eve batteries. We currently have 100w of Sunpower and dont expect to get much more than an additional 200w. I have modified a delco remy SI28 160a to external regulation satisfying LFP. I will reduce it to less than 100a output with belt manager.
I hadnt thought I needed the added 280a of battery with the alternator, but will see if I can add it in the cabin locker which is limited in space.
I didnt want to put it under the seatee because its too difficult and tight.
First step is to get the first batt installed.

Newhaul, your long and mean has more solar now. ...ours short and stubby 32', but solid.

[newhaul]

Originally Posted by rgleason

S/v Jedi.
You have my situation just about right. We use propane, have ozifridge, and autopilot and B&G radar. I was considering 280a of Eve batteries. We currently have 100w of Sunpower and dont expect to get much more than an additional 200w. I have modified a delco remy SI28 160a to external regulation satisfying LFP. I will reduce it to less than 100a output with belt manager.
I hadnt thought I needed the added 280a of battery with the alternator, but will see if I can add it in the cabin locker which is limited in space.
I didnt want to put it under the seatee because its too difficult and tight.
First step is to get the first batt installed.

Newhaul, your long and mean has more solar now. ...ours short and stubby 32', but solid.

By that I msan if 29 ft long and only 8 ft beam designed to MORC standards a racing type that no longer exists on a large scale

Just looked and I'm 2500 pounds lighter but about 250 pounds more lead.

[RaymondR]

Would putting one of these across the output of an alternator suppress the transient when the BMS disconnected?