Lithium batteries with Windlass

[zboss]

Folks,

I was noticing that the nominal max amp draw on lithium batteries is 100 amps, which is below the max draw of [at least our] windlass.

How do you manage this discrepancy?

- z

[senormechanico]

3C is the max.
For example, if you have 100 aH cells, you can draw up to (or charge at) 300 amps.

[witzgall]

It depends on the actual cells, not all lithium is the same, even if they are the same chemistry. I have seen lifepo4 specifications ranging from 1c to 10c discharge rates.


Sent from my iPhone using Cruisers Sailing Forum

[zboss]

The ones I was looking at were 100 amps... Smart Battery. It seems like most manufacturers do not directly publish their max discharge rates.

[hzcruiser]

What's the capacity and is it a LiFePo (or LFP) batt? You just mentioned "Lithium"...

The datasheet of the manufacturer has to have more details; if you can't get or find it, I'd stay away from the batt as it might be some knock-off.

To answer your question:
In general, LFPs don't get damaged even when you try to draw more than they can deliver. What will happen is the same as what happened with your old lead acids: the voltage will go down (more than it would anyway). You'll hear the windlass go slower or stop altogether.

Happened to me a lot with the old LA batt. Most windlasses are ok with a collapsing voltage, just take your foot off the power switch as soon as it slows down considerably.

[zboss]

For example... Mastervolt doesn't seem to list a max amp draw.

http://www.mastervolt.com/products/l...a-12-2500/pdf/

[hzcruiser]

Looks very fancy! But USD3600 ? For one ? Give me a break...

[zboss]

Originally Posted by hzcruiser

Looks very fancy! But USD3600 ? For one ? Give me a break...

I don't know.. Bruce Schwa sells the Genasun 200 amp/hr battery for $4900 and the Mastervolt is 180 amp/hr.

I think both are "systems" though...vs the smart battery which is just the battery.

[Viking Sailor]

Originally Posted by zboss

For example... Mastervolt doesn't seem to list a max amp draw.

http://www.mastervolt.com/products/l...a-12-2500/pdf/

After reading the above spec's it looks like you can give it a try without damaging the battery. It is designed to allow "Ultra-fast charging and discharging", and has integrated "Switch off relay controls".

[Maine Sail]

Originally Posted by zboss

The ones I was looking at were 100 amps... Smart Battery. It seems like most manufacturers do not directly publish their max discharge rates.

PLEASE check out the BBB rating of Smart Battery. I believe the current limit is not driven by the battery cells but rather the marginal built in "BMS" on that product...

[hzcruiser]

Originally Posted by Maine Sail

PLEASE check out the BBB rating of Smart Battery. I believe the current limit is not driven by the battery cells but rather the marginal built in "BMS" on that product...

Oh, the webserver just gave me a "Database error" back....

Anyway, what is the BBB rating, if I may ask?

The built in BMS would most likely cut off at HVC and LVC (high/low voltage cut off) plus a temperature sensor to avoid high charging currents when the batt temp is too high and no charging when the batt is below 0C freezing point.

[GordMay]

BBB = Better Business Bureau

Smart Battery, LLC is not BBB Accredited, is rated F, and has had 32 complaints closed with BBB in last 3 years | 22 closed in last 12 months.
➥ Consumer complaints for Smart Battery, LLC - West Coast Florida BBB.

[zboss]

Originally Posted by Maine Sail

PLEASE check out the BBB rating of Smart Battery. I believe the current limit is not driven by the battery cells but rather the marginal built in "BMS" on that product...

I'm not actually looking to change right now... I'm just getting familiar with the technologies and issues for when we do switch out 3 to 5 years from now. I do think we will see a big price drop for these types of batteries in the next few years, making them a viable option for many cruisers.

I was curious about the windlass because I was under the impression that you could pull pretty much any about of power of of a lithium as required. Right now we have our windlass connected to our house batteries and although the pull is significant the overall amp utilization is small. 5 minutes of use only uses 15 or so amps and thats assuming I had to re-anchor... it certainly doesn't take me 5 minutes to anchor most of the time.

[Maine Sail]

Originally Posted by zboss

I was curious about the windlass because I was under the impression that you could pull pretty much any about of power of of a lithium as required. Right now we have our windlass connected to our house batteries and although the pull is significant the overall amp utilization is small. 5 minutes of use only uses 15 or so amps and thats assuming I had to re-anchor... it certainly doesn't take me 5 minutes to anchor most of the time.

Again it is not the cells or battery that are the limitation here it is the corner cutting nature of a "drop in" LFP battery.

The 100A limit is imposed by the contactors or switches used inside the battery to protect it. In order to protect itself all charge and discharge current are fed through one contactor/switch which is inside the case.

When you do this externally, as you ideally should, your options for contactors/relays/switches, and their amperage ratings, are much broader and can be purposely chosen to fit the application.

For example our main bank protection contactor is 500A continuous rated and can handle 2000A inrush current for starting motors or engines. The Smart Battery uses low rated switches because it is a poorly engineered solution that was never well thought out or intended as a cruising bank.... A 300Ah LFP battery with a max charge or discharge rate of 100A......? If that battery was $500.00 I would still not even consider it.... Probably okay for a bass boat but a thruster, windlass or massive inverter......???

While our 400Ah LFP bank can handle a continuous discharge rate of 3C (1200A) I am limited to 500A by my contactor. For "impulse current" eg: motor starting the bank can handle a 10C load or 4000A but my contactor can only handle 2000A.... I have no need to go larger than a 500A contactor but a 100A max continuous switch rating is simply corner cutting engineering for an LFP bank, at least IMHO.

[hzcruiser]

Originally Posted by zboss

I'm not actually looking to change right now... I'm just getting familiar with the technologies and issues for when we do switch out 3 to 5 years from now. I do think we will see a big price drop for these types of batteries in the next few years, making them a viable option for many cruisers.

Yes, I'd agree with you, LFP (or LiFePo4) is the future batt technology for bulk storage on boats. Prices will come down a bit but demand will increase, too, hence I wouldn't "just wait" but do the math whether the higher price is acceptable once you include the longer life span (cycles) and higher DOD (less capacity needed). Then you also save some weight by switching to LFP.

On the con side it's not easy or simple to mix them with lead acid batts in parallel and the charging voltage should ideally be higher than for lead acids.

I would prefer a system where I could gradually replace old and inefficient lead acids with LFPs rather than in one big and expensive hit.