Lifepo4 bow thruster batteries, which BMS?

[sailing gal]

So, I am reading this thread as I have an issue with my bow thruster as well. I recently replaced my house bank with two 200 Ah LFPs. I have an AGM installed as a start battery completely isolated from the house bank. I tried to run my bow thrusters after having the props cleaned. I initially ran them while plugged in to the dock. I have a 60A charger. I found a failed relay- port side worked, starboard side did not. I brought an electrician on-board. He found the failed relay. I also tried to run the bow thrusters without shore power. The BMS turned off the batteries. I emailed the battery manufacturer and he suggested I use an AGM battery for the bow thruster to get adequate CCA. I have a 100 Amp Balmar alternator and a serpentine belt system on my Yanmar 78 Hp engine. So, here are my questions for you guys who I suspect are more familiar with LFPs than my marine electrician, who is the best one in this area.
1. Could the LFP system, while plugged into shore power, have caused the relay to fail while testing it at the dock, or was this just another one of those marine coincidences. My electrician says that he has found Sleipner thrusters to be extremely power sensitive. He thinks he can fix the relay circuit board. Here's hoping....
2. Should the system be able to handle the bow thruster if the engine is running (which is normally the case). In other words, will the alternator make up the cranking deficit?
3. If there should be an emergency and no engine, I can combine my house bank with my starter battery with an intermittent button at my helm. I am considering replacing the intermittent switch with a pull on/push off switch so if I had to use the bow thruster without an engine, I wouldn't need 3 hands.
4. I assume I am going to have the same issue with my windlass. Of course, I usually have the engine running when operating the windlass, but for enough cranking (I have a 1700 watt windlass) would I need to combine the banks again? OR- will just running the engine give me enough cranking power to get the LFPs through the ritual?

To add to this, the battery manufacturer said that because of the nature of a bow thruster, on/off/on/off, it should be constantly connected to an AGM battery, the engine running was not adequate. So, I am thinking again about changing that combining switch to allow a longer interconnection between house and start battery.

Thank you for any assistance in this, I would really hate to add another battery bank in the bow.

 

[greyghost]

I'm happy to assist, but I'll need answers to a few questions first.

1. What is the max continuous rating of the BMS for each battery? Are they drop-ins or DIYs? Brand?
2. Your windlass draws 1700W. What does your bow thruster draw?

I can't say if your relay failure is related to your current system or not. I tend to think not, but will let someone with in-depth knowledge of relays add their comments here.

If your thruster was operating properly off the AGM/SLA house bank before you moved to LFPs, then one item immediately comes to mind. 400Ah of LFP should be more than sufficient to operate your thruster. My suspicion is you are exceeding the rated capacity of the BMS(s) when operating your thruster.

lmk your answers to the questions above and we can go from there.

Cheers,
Doug

 

[sailing gal]

Hi Doug,
Thank you for the response. The 200 Ah LFPs ( I have two of them in parallel) have a 100A continuous discharge rating each as well as a 100A charge current. They are RJ batteries (China). I was not running my engine at the time of the issue, but I have a 100A Balmar output alternator with a serpentine belt. When the boat was plugged in, it ran- I have a 60A battery charger that was on at the time. It was when I attempted to run the bowthruster without being plugged in and without running the engine that everything went dark and the batteries turned off. Of course, normally, I would be running the engine when running the bow thruster, but I am thinking about emergency situations.

The bow thruster is a 4 kw thruster with a 480A current draw and 550 CCA. The wiring from the battery bank to the thruster is thick battery cable- oversized for the distance and I never had an issue with current when I had an AGM house bank. The house bank is about 3 meters from the thruster motor.

My electrician/engineer is thinking that we can avoid adding an AGM battery to handle it if he modifies the relays and installs a soft-start module on the bow thruster which he says would just delay the start up by one to one and half seconds. He thinks the failure of one of the relays so that only one side of the bow thruster worked is an unrelated issue. He is one of the best electrician/electronics gurus I have ever met- very creative and quite capable, but not a lot of experience with LFPs. He can program circuit boards and make just about anything work.

I suspect the windlass is not going to be a problem because it draws so much less power.

Any suggestions are welcome.

Thank you for your response-
Wendy

 

[greyghost]

Wendy,

Your anchor windlass max draw (1700W/12V=142A) is within the specs of your current house battery bank, and should operate properly.

Your thruster will require something like 4000W/(12 to 13V) = 308 to 333A max in operation. As Turd Ferguson pointed out higher up, this is likely the 'stalled' amperage and operating amperage could well be less. Still, I would suggest 350A as the minimum design criteria for a robust system. Higher if you can for greater headroom in the event your electrical system, for whatever reason, isn't in perfect shape.

You have 200A continuous available from your house bank. You might have somewhat more on a momentary basis but, judging from your 'lights out' experience, clearly not enough. Your batteries' BMSs likely shut them down due to overcurrent. Even with your engine running at full alternator capacity (unlikely since you'll probably be idling when using the thruster), you are just reaching the minimum design limit.

Your electrician might be able to reduce the inrush current when the thruster starts up by adding a soft-start module. However, this isn't likely to resolve your primary issue which appears to be the inability of your current system to provide the continuous operating current you need. I would place thruster use in the area of 'continuous' duty, even though it often feels like 'momentary' use. After all, it doesn't help if you need a second burst of thruster shortly after the first, and your BMS says 'NO'. Or if you need to lay on it for 10 or 15 seconds (or longer) to correct for a fudged high wind or cross-current landing. Bottom line...You'll need to find a way to provide this continuous current to your thruster if you wish to have confidence in its operation. Many thrusters will 'time-out' due to heat issues after 5-7 minutes use, so a LV disconnect due to total current draw from your house bank isn't likely to be a significant issue, unless your house bank is at low SOC to begin with.

You could add an AGM battery (recommend 200A minimum) near the thruster, though even this can be sub optimal. From my own experience, two nearby 120Ah AGMs can provide both the CCAs and continuous current such a thruster requires, but voltage sag under repeated use can result in successively slower operating speeds. As well, I've found long term battery survival isn't great.

Do you have room to add two more RJ batteries to your house bank?

Cheers,
Doug

 

[Jan Gils]

LMK if you come across a BMS which can monitor the cells of 8 individual 3P4S batteries, which has the ability to simultaneously control 2 Victron MultiPlus 3000s, an MPPT, alternator field disconnect, bluetooth monitoring...

Look up Batrium for BMS. The watchmon 4 series can do all this. It supports every battery setup, with monitors on each cell. It can talk to Victron equipment using CANBUS (Multiplus, MPPT, ...), you can even use the relay outs to trigger the victron equipment.

 

[pretzel]

@greyghost, et al.
I added a new topic that crosses over well with this thread if anyone here would care to join in

LFP system design with interconnected LFP windlass bank

This is for an Island Packet 380 sailboat. It’s currently outfitted with 3x AGM’s for the house, and 2x AGM’s for the windlass/thruster. Everything is 12v. Here’s the system I’ve been sketching out: House battery: 4P4S EVE LF304Ah LFP cells Windlass/thruster battery: 1P4S EVE LF304Ah LFP cells...

diysolarforum.com

 

[captainrivet]

Wendy,

Your anchor windlass max draw (1700W/12V=142A) is within the specs of your current house battery bank, and should operate properly.

Your thruster will require something like 4000W/(12 to 13V) = 308 to 333A max in operation. As Turd Ferguson pointed out higher up, this is likely the 'stalled' amperage and operating amperage could well be less. Still, I would suggest 350A as the minimum design criteria for a robust system. Higher if you can for greater headroom in the event your electrical system, for whatever reason, isn't in perfect shape.

You have 200A continuous available from your house bank. You might have somewhat more on a momentary basis but, judging from your 'lights out' experience, clearly not enough. Your batteries' BMSs likely shut them down due to overcurrent. Even with your engine running at full alternator capacity (unlikely since you'll probably be idling when using the thruster), you are just reaching the minimum design limit.

Your electrician might be able to reduce the inrush current when the thruster starts up by adding a soft-start module. However, this isn't likely to resolve your primary issue which appears to be the inability of your current system to provide the continuous operating current you need. I would place thruster use in the area of 'continuous' duty, even though it often feels like 'momentary' use. After all, it doesn't help if you need a second burst of thruster shortly after the first, and your BMS says 'NO'. Or if you need to lay on it for 10 or 15 seconds (or longer) to correct for a fudged high wind or cross-current landing. Bottom line...You'll need to find a way to provide this continuous current to your thruster if you wish to have confidence in its operation. Many thrusters will 'time-out' due to heat issues after 5-7 minutes use, so a LV disconnect due to total current draw from your house bank isn't likely to be a significant issue, unless your house bank is at low SOC to begin with.

You could add an AGM battery (recommend 200A minimum) near the thruster, though even this can be sub optimal. From my own experience, two nearby 120Ah AGMs can provide both the CCAs and continuous current such a thruster requires, but voltage sag under repeated use can result in successively slower operating speeds. As well, I've found long term battery survival isn't great.

Do you have room to add two more RJ batteries to your house bank?

Cheers,
Doug

With windlass and bower thrusters I highly recommend to put an amp clamp meter with 600A range, set it up for max. Reading and measure while you use them. They have a much higher start up current and also a so called inrush current. My lofrans cayman 12V/1000W shows a start up current up to 320A and inrush when stopping around 380A wile using 114A during normal operation. Your 4300W bowtruster is worse, expect around 700-800A….this will fry every BMS that carries current. If you wanna run this of your LifePo4 house Electrodacus BMS is perfect.

I suggest to put 18 cells 40AH Linglong LTO in a 3P6S config so a 12V/120AH with a Electrodacus BMS, that can handle these loads.