Lithium to power thruster

[OceanStateTunin]

I didn't consider doing multiple runs of wire due to length and possibly if an end had a bad connection or something turning the other wires into a light bulb but I do suppose that is an option... having extra reserve capacity on house bank does excite me a little if I was doing it the way I was saying, should that even work.

[JustMurph]

In an ideal world you wouldn't do multiple runs, that was just for the cost comparison, as most of the cost is in the copper.

[Baronkrak]

Originally Posted by Whatta Life

i had same issue, here is how I got around it. I built my own lfp battery with bms. 500a bms is available but expensive. Used a smaller bms for charging and balancing but hooked the bow thruster directly to battery. I don't use the bow thruster for more than 30 seconds at a time so there is no way I'm going to drain the battery too low. Nothing else is attached to drain the battery so don't have to worry about it. Bms handles charging protection and balancing( you can use a small bms)

So you have an unprotected lfp when using the bow thruster?

[JustMurph]

The biggest risk there is a failure in the switches or relay for the bow truster resulting in it being unintentionally stuck on. If this happened while the boat is unattended, the battery could run flat. I've had this happen to be with my windlass when I forgot to isolate it and the deck switch failed.

[Whatta Life]

I have had no problems with it. But I did switch over t0 lithium titanate (LTO). no problem with the LFP just had a bunch of LTO sitting around and decided to use it( LTO can easily to 10c, so small battery works great) Plus LTO can be discharged down to 0 volts without hurting it, so don't have to think about keeping it charged. I think having a battery next to windless is a good idea and being able to use a small bms makes it inexpensive to install.

[gpeacock]

Mere mortals aren't going to be playing with LTO cells. (Nor should they be)
Most of us shouldn't even be playing with raw LFP (LiFePO4) cells but if you understand some electrical basics it can be done perfectly safe.

So back to powering the Thruster (and ultimately windlass as well).
My 12V thruster pulls 500A. If I'd had time to think about it I would have gone with a 24V system to drop this crazy draw down but I didn't...

Option 1: You can attach up front, a good quality starter battery of your preference matched to this load. If using a drop in LFP 12V battery pay close attention to the max rated load. Most are not up to the task. You then can run smallish wires and a DC-DC charger. The bigger the DC charger the bigger the wires but also the more power you'll be able to supplement from your engine/house/start bank. Dont forget to consider venting if using FLA and all of the extra costs around required fuses, battery switches etc... I would caution against not using a DC-DC charger and thinking about an ACR or similar device instead... You'll struggle getting these devices to work properly with a House LFP bank (see my experience below).

Option 2: Use your LFP house bank to power things up front. Assuming your house bank can handle the load, run the big wires up front to minimize the voltage drop. For a thruster 3% is totally acceptable, most thrusters will be fine with 5%. If you have a bunch of 12V drop in LFP's then do the math and sort out your max draw. Keep in mind that in general a thruster load should be on for no more than 10s at a time and you'll have some help from the alternators while running it. If you are using bare cells, there are lots of BMS's that dont run current through them and thus aren't restricted. It would be the contactor that needs to be rated for the load. Chargery, Electrodacus, Orion, Batrium, Smart123, RecBMS, Tao to name just a few. Some are expensive, some are not. It is easy to set your Battery protect parameters on any of these to deal with the high load of a thruster.

FWIW: I started with option 1 until I got LiFePO4 cells 10 years ago. At the time my forward battery was AGM and had just been replaced. I tried to use an ACR to connect it while the house bank was getting charged. I struggled with two things: Even being right next to the thruster, the AGM bank wouldn't do its share of work and because I had the small wire running forward from the house bank fuse appropriately I kept blowing the fuse. Also the ACR always thought the LFP bank was getting charged (higher resting voltage) so it was ultimately connected all the time. I simplified everything then and quickly moved to Option 2. I ran a Chargery BMS with no problems for many years but recently dissolved it in water and am now considering something a little more advanced like an Electrodacus or maybe even the Batrium BMS.

[s/v Jedi]

Originally Posted by gpeacock

Mere mortals aren't going to be playing with LTO cells. (Nor should they be)
Most of us shouldn't even be playing with raw LFP (LiFePO4) cells but if you understand some electrical basics it can be done perfectly safe.

So back to powering the Thruster (and ultimately windlass as well).
My 12V thruster pulls 500A. If I'd had time to think about it I would have gone with a 24V system to drop this crazy draw down but I didn't...

Option 1: You can attach up front, a good quality starter battery of your preference matched to this load. If using a drop in LFP 12V battery pay close attention to the max rated load. Most are not up to the task. You then can run smallish wires and a DC-DC charger. The bigger the DC charger the bigger the wires but also the more power you'll be able to supplement from your engine/house/start bank. Dont forget to consider venting if using FLA and all of the extra costs around required fuses, battery switches etc... I would caution against not using a DC-DC charger and thinking about an ACR or similar device instead... You'll struggle getting these devices to work properly with a House LFP bank (see my experience below).

Option 2: Use your LFP house bank to power things up front. Assuming your house bank can handle the load, run the big wires up front to minimize the voltage drop. For a thruster 3% is totally acceptable, most thrusters will be fine with 5%. If you have a bunch of 12V drop in LFP's then do the math and sort out your max draw. Keep in mind that in general a thruster load should be on for no more than 10s at a time and you'll have some help from the alternators while running it. If you are using bare cells, there are lots of BMS's that dont run current through them and thus aren't restricted. It would be the contactor that needs to be rated for the load. Chargery, Electrodacus, Orion, Batrium, Smart123, RecBMS, Tao to name just a few. Some are expensive, some are not. It is easy to set your Battery protect parameters on any of these to deal with the high load of a thruster.

FWIW: I started with option 1 until I got LiFePO4 cells 10 years ago. At the time my forward battery was AGM and had just been replaced. I tried to use an ACR to connect it while the house bank was getting charged. I struggled with two things: Even being right next to the thruster, the AGM bank wouldn't do its share of work and because I had the small wire running forward from the house bank fuse appropriately I kept blowing the fuse. Also the ACR always thought the LFP bank was getting charged (higher resting voltage) so it was ultimately connected all the time. I simplified everything then and quickly moved to Option 2. I ran a Chargery BMS with no problems for many years but recently dissolved it in water and am now considering something a little more advanced like an Electrodacus or maybe even the Batrium BMS.

Why do you say that about LTO? They are the safest option available, won’t even ignite when you incinerate them.

No, LTO is the preferred option but some DIY work and TPPL AGM as #2 and drop-in easy.

[gpeacock]

Originally Posted by s/v Jedi

Why do you say that about LTO? They are the safest option available, won’t even ignite when you incinerate them.

No, LTO is the preferred option but some DIY work and TPPL AGM as #2 and drop-in easy.

I will easily concede that LTO cells aren't any more dangerous than LFP but they are pretty hard to work with in a 12V environment. 6 Cells in series means a voltage range from 15V to 11.4V. Pretty tough to manage with most normal boat equipment. 4 cells of LFP runs from 14.4-11.6. Standard 12V gear works fine with that range.
Going up to 24 or 48V system voltages does help with this issue.

Also, I've never seen any cells in greater capacities than 40AH which means a much more complicated parallel/series build and all the pitfalls that comes with that. Add expense per wh and I feel there just aren't enough manufacturer partners out there to make it work well in boat applications unless you are willing and knowledgeable to fully take care of all the details.

[s/v Jedi]

Originally Posted by gpeacock

I will easily concede that LTO cells aren't any more dangerous than LFP but they are pretty hard to work with in a 12V environment. 6 Cells in series means a voltage range from 15V to 11.4V. Pretty tough to manage with most normal boat equipment. 4 cells of LFP runs from 14.4-11.6. Standard 12V gear works fine with that range.
Going up to 24 or 48V system voltages does help with this issue.

Also, I've never seen any cells in greater capacities than 40AH which means a much more complicated parallel/series build and all the pitfalls that comes with that. Add expense per wh and I feel there just aren't enough manufacturer partners out there to make it work well in boat applications unless you are willing and knowledgeable to fully take care of all the details.

But this thread is about a bow thruster, not “normal boat equipment”. You simply use 5 or 6 cells in series according to the needed voltage and program the dc-dc charger accordingly.

Also, 40Ah is more than enough.

[mvweebles]

LFP engine start battery would work. 2000 cranking amps (not sure exactly what that means) and 80 Ah capacity. $1349 USD. I use a smaller version of this battery for my 20hp OB with electric start and tilt. Works great.

https://antigravitybatteries.com/pro...tive/ag-h8-rs/

That said, I'm in the camp of sealed lead acid is great for starter motor type loads. They are inexpensive and easily replaced anywhere in the world. Hard to do with AGMs. Can be impossible with LFPs. I have solar that keeps it topped off easily.