LiFePo Query

[Frayed Knot]

Like many, I’m becoming quite tempted by the idea of converting to the above as we cruise & mostly anchor for about three months per year.
I’ve read up on the subject quite a bit, sorted the useful from the obviously ill-informed, and I think I now have a fair idea of the pros & cons - (not many cons) for replacing the domestic bank.
A question I’m having trouble finding an answer to is: would these batteries be suitable to run a bow thruster & windlass? (hopefully not at the same time)
At present I have 2 paralleled 12v 100ah sealed lead acid type with a B2B charger right forward - far from ideal weight wise but giving more than adequate capacity.
Obviously a single, lighter lithium would be a huge improvement if it would do the job. The windlass, used frequently, is 1500w & typically runs for about two minutes. The thruster, seldom used but occasionally vital, draws 650 amps & is rarely in operation for more than five seconds.
Any advice welcomed.

 

[B27]

I don't think a generic answer will be much use.
You could build or buy a bank which will do these currents, OTOH smaller cells and 'drop in' solutions are not rated for such current.

 

[Sandy]

What do your current batteries do?

I've always used windlass with the engine on.

 

[geem]

Most FET based lifepo4 batteries have current handling limitations of circa 200A. Running windlass and thruster loads is likely to trip the BMS on its high current limit. The inrush current of DC motors is considerable. Far higher than the equivalent AC motor.
You would be better running high DC loads from the engine battery since the engine will be running at the same time and the alternator can offset some of the load.
We don't have a thruster but our 1700w windlass motor runs from the engine batteries. Being a 24v boat we have 2x105Ah 12v engine batteries wired in series. Their large capacity easily deals with the load of the windlass
It may be worth uprating your engine battery to a larger size to accommodate the additional load.

 

[Kelpie]

The thruster, seldom used but occasionally vital, draws 650 amps & is rarely in operation for more than five seconds.

That's a huge amount of power. What voltage?

 

[rogerthebodger]

That's a huge amount of power. What voltage?

My bow thruster draws about 600 Amps at 12Vdc supplied by LA bat tries.

I am interested in this question as I am also looking changing to LifePO4 at some point

 

[Kelpie]

I didn't realise bow thrusters drew that much power.
Most LiFePO4 batteries are only rated for 1C discharge, so if you want to draw 650A, you need 650Ah of batteries.
It's one of those applications where lead acid makes more sense, to me. Same for windlasses and engine starting.

 

[noelex]

It can be done with good quality lithium cells (for example Winston) teamed with a BMS driving an external contactor. Winston cells are rated for 3C continuous and 10C "impulse" discharge.

It is not feasible with simple drop-in solutions. The best (and perhaps the only option) is a DIY battery. It needs premium products to manage this level of current so it will be expensive to construct, but it is possible.

 

[noelex]

My bow thruster draws about 600 Amps at 12Vdc supplied by LA bat tries.

I am interested in this question as I am also looking changing to LifePO4 at some point

The specifics of the installation are important. For example, if you drive the bow thruster from the house bank (rather than forward batteries), the C discharge rate becomes more manageable. It can then become feasible with cheaper components.

So be careful applying information regarding a specific question unless your installation is very similar.

 

[Frayed Knot]

Many thanks for these replies & advice. I realise that there are many variables and at this point I’m just looking for general advice (plus that one specific) to help me to research/plan, which is exactly what I’ve just received
In light of this advice I’m now thinking that doing away with the dedicated batteries may be the way to go but at 12v (Kelpie) with a distance between engine battery & thruster of about 8m & another 2m to the windlass the cable sizes will need to be massive.

 

[Frayed Knot]

It can be done with good quality lithium cells (for example Winston) teamed with a BMS driving an external contactor. Winston cells are rated for 3C continuous and 10C "impulse" discharge.

It is not feasible with simple drop-in solutions. The best (and perhaps the only option) is a DIY battery. It needs premium products to manage this level of current so it will be expensive to construct, but it is possible.

Could you clarify (put into idiot-terms) 3C & 10C discharge, please?

 

[Kelpie]

Could you clarify (put into idiot-terms) 3C & 10C discharge, please?

3C means it can discharge at three times it's Ah capacity. So a 100Ah battery can provide 300A of current. And 10C can provide ten times as much.

Note that lead acid batteries are easy way better at this. Even a small car battery can provide hundreds of amps for a short period- the CCA rating.

I'm a big fan of lithium but I don't think they're the right choice for high current, short duration loads.

My windlass uses about 2.5Ah each time I lift the anchor. But to power it with lithium I'd need a 120Ah battery minimum, more like 150Ah for a bit of margin. So I'd be paying to carry around a big lithium battery that could lift the anchor hundreds of times without even needing charged. It can work, but why do it when a £60 car battery will do the job?

 

[Refueler]

Could you clarify (put into idiot-terms) 3C & 10C discharge, please?

The battery C Rating is the measurement of current in which a battery is charged and discharged at. The capacity of a battery is generally rated and labelled at the 1C Rate (1C current), this means a fully charged battery with a capacity of 10Ah should be able to provide 10 Amps for one hour.

 

[noelex]

The C-rate is a term that relates the capacity of the battery in Ah (amp-hours) to the discharge (or sometimes charge) current.

A maximum continous discharge of 3C means if you use 200 Ah Winston lithium cells (the same capacity as your existing lead acid bank) the maximum continuous discharge current would be:

3 x 200 = 600 A

The maximum "impulse current" is 10C or:

10 x 200 = 2000 A

This rating is just for the cells of the battery. For a complete battery a BMS is also required. The BMS will also have a maximum current limit that cannot be exceeded. To work with high currents, the best solution is to have the BMS control a contactor (a large relay) so the current does not pass directly through the BMS itself. Therefore the maximum current is limited by the specifications of the contactor. There are some BMS units that will do this, but they tend to be expensive and there is added expense of the contactor Itself.

A popular choice for the contactor in high current systems is the BlueSea ML remote battery switch. This is a latching relay so consumes no power other than when switching states.

It is rated at 500 A continuous, 700 A for five minutes, or 1450 A for 30 seconds.

 

[Refueler]

3C means it can discharge at three times it's Ah capacity. So a 100Ah battery can provide 300A of current. And 10C can provide ten times as much.

Note that lead acid batteries are easy way better at this. Even a small car battery can provide hundreds of amps for a short period- the CCA rating.

I'm a big fan of lithium but I don't think they're the right choice for high current, short duration loads.

My windlass uses about 2.5Ah each time I lift the anchor. But to power it with lithium I'd need a 120Ah battery minimum, more like 150Ah for a bit of margin. So I'd be paying to carry around a big lithium battery that could lift the anchor hundreds of times without even needing charged. It can work, but why do it when a £60 car battery will do the job?

You forget that C rate is actually Amps over Time ...... ie Amps per Hour ratio.

Second : Lithium based batterys ARE capable of and used for high Amp rate loads - but limitation is created by the BMS system employed on the cells as well as fact that cells are manufactured to deliver a load ... ie C rate .... and can be constructed for low or very high.....

Third : People often mistake C rate to mean Charge as well as Discharge rate. The two are NOT the same. C rate is usually quoted for Discharge rate ... with not always a Charge Rate quoted as well. It is common that Charge C rate is seriously lower than Discharge C Rate ...

 

[Frayed Knot]

Hmmm, thank you all. That just about settles that then; I think I’ll leave the thruster/windlass bank as it is as the cabling to run them from the engine battery (the ideal solution) would cost a fortune!

 

[gregcope]

Hmmm, thank you all. That just about settles that then; I think I’ll leave the thruster/windlass bank as it is as the cabling to run them from the engine battery (the ideal solution) would cost a fortune!

I was going to suggest something like this.

Ie consider using a hybrid and the LifePo4 for the domestic loads and some FLA combination for the engine/thruster. I run my windlass off my LifePo4. Does not trip the mosfet based BMS (two @175A limit, will need to check the burst limits. These are 200A JBD bms(es)).

 

[Zing]

Like many, I’m becoming quite tempted by the idea of converting to the above as we cruise & mostly anchor for about three months per year.
I’ve read up on the subject quite a bit, sorted the useful from the obviously ill-informed, and I think I now have a fair idea of the pros & cons - (not many cons) for replacing the domestic bank.
A question I’m having trouble finding an answer to is: would these batteries be suitable to run a bow thruster & windlass? (hopefully not at the same time)
At present I have 2 paralleled 12v 100ah sealed lead acid type with a B2B charger right forward - far from ideal weight wise but giving more than adequate capacity.
Obviously a single, lighter lithium would be a huge improvement if it would do the job. The windlass, used frequently, is 1500w & typically runs for about two minutes. The thruster, seldom used but occasionally vital, draws 650 amps & is rarely in operation for more than five seconds.
Any advice welcomed.

I have a DIY lithium set up, which powers the bowthruster very well. With lead there was a large volt drop and speed and power drop to match, plus almost unusable if the batteries were low. Not so with lithium. Full speed even when nearly flat. My BMS has no overcurrent limit and that’s essential. I rely on fuses.

 

[miracze]

Hi,
I went for hybrid system using Emily & Clark's Adventure - BankManager™ BBMS and I'm very happy with it. High loads of windlass / bowthruster goes from lead and house bank is powered by "cheap" DIY aliexpress battery with 80A BMS. You don't need to change chargers / solar regulators which can be significant amount of money.

 

[Neeves]

I am very conscious of the costs involved with a new Lithium installation and suspect many are going to conduct the initial research and then back away - on an oldish yacht (not sure how old) the Lithium costs are going to become a large part of the yacht costs - and they may back away. Any way of cutting the costs, which means ignoring the thought that the only colour is blue (aka 'Victron everything'), must be worth exploring and not rejecting out of hand.

Assuming the lithium battery bank is a retrofit then it does seem a complete waste of money to dump the charging and control of the old Lead. It presumably currently works and the prompt to consider the installation of a Lithium bank is because the lead is old and needs replaced. Lead batteries are cheap - simply replace the Lead commensurate with what is needed, windlass, engine start, bow thruster (I had not realised the number of people with bow thrusters) and simply replace the domestic demands. I note that people are using Lithium for high demand components, engine start, bow thruster etc - but I have no take on that. My understanding is you do need to invest as you might want a B2B charger, battery monitor + shunt, etc and you may need to change or add to your solar charging control.

It is likely that the old electrics were 12v - I don't know what the issues are with having a 12v lead and a 24v Lithium (one of the recommendations if you are investing in Lithium is to go 24v).

The big issue might be space, where to locate the extra kit. Hopefully your old battery bank can be reduced in size and the Lithium bank take up no more room than the retired old Lead units.

If its a new yacht - different story - but if its a new yacht the commissioning team should be doing the electrics, not you as owner.

Jonathan