T-Pain Is On A Boat

On Tuesday, September 13, 2022 at 11:39:24 PM EDT, bobkart <couch45@msn.com> wrote:

Good stuff Matt; thanks! Can you recommend a brand or two from your 'never had a fire' list?

My current pack is 48V nominal, 10kWh LFP (16S DIY). Working on a second, 5.3kWh pack with better energy density at the moment (Gotion 105Ah cells). Motor is 6kW (ePropulsion). Something in the 5-10kWh range would be ideal and allow scaling.

Re: [electricboats] NMC Onboard?

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Re: [electricboats] NMC Onboard?

IMO I'm pretty ok if its an OEM boat/battery. There are certain NMC manufacturers that don't (at least that I can find) have a single battery fire to their name. DIY its tempting but I do not think its worth it. I have a variety of NMC batteries in my shop with a great form factor and energy density. You could put 20kw in say a 30' boat without much effort at all. Including the motor you would probably still weigh less than a full tank of fuel and a diesel.

In a few months CATL will be shipping lifepo that rivals NMC energy density. Exciting times.

Matt Foley

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

On Tuesday, September 13, 2022 at 09:55:37 PM EDT, bobkart <couch45@msn.com> wrote:

What are people's thoughts on the use of NMC versus LFP on a boat, for propulsive power?

NMC has considerably better energy density (by mass), but of course is less safe from a thermal-runaway standpoint.

The supplier I'm considering says the 'flash point' of his cells is 400C ("close to LFP" he says), but I see more like 300C for NMC and 500C for LFP (round numbers).

I'm attracted to the better energy density of NMC, but don't want to endanger our lives by moving to it.

[electricboats] NMC Onboard?

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Re: [electricboats] Maximum input voltage for outboard?

Good call Matt, looking at the spec sheet. I only looked over the specs on the main product page.

So they say "built on patented Lithium Iron Phosphate (LiFePO₄) chemistry" on the main product page, but then say "built on patented Lithium Iron Manganese Phosphate chemistry" on the spec sheet. The latter seems to have too many ingredients in it. I do notice that 7 x 3.7V nominal is the 25.9V nominal they claim on the spec sheet. That's consistent with a 7S NMC arrangement. 8S LFP would come to 25.6V nominal. NMC would also explain the apparent great energy density (for LFP) that I noticed. No trouble at all to get that energy density with NMC.

You should definitely follow up on this with the supplier. Easiest way to answer the question would be to open the case, but that's likely going to void the warranty and compromise the case waterproofness. X-Ray perhaps?

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Re: [electricboats] Maximum input voltage for outboard?

Hi Jim,

Now my interest is really piqued!

There is zero chance your batteries would be sitting at 29 volts in a partial charged state. Even at 100% soc they would fall below 29v within a minute after taken off the charger and they would keep falling 26ish volts. While often not followed, Lithium batteries are supposed to be shipped at no more than 30% soc, fyi.

The specs on the link you sent seem perfectly in line with 8s lifepo4. Click on the "Download the Lithium Battery Spec Sheet" link. Scroll down to the Battery Management System. This is where things get weird. They say per cell "over voltage protection" is 4.3v. This would be a correct (even a little high) for an NMC chemistry battery. I have seen manufactures put in high upper limits to make up for bottom of the barrel cells, but never this high. What's even more concerning is the "over charge release voltage" of 4.1. This means the cell will cycle between 4.1 and 4.3. It should never go above 3.65.

I would say they just put the wrong specs on this page, but this does not explain your abnormally high voltage. You either have an unusual number of cells in series (highly doubtful) or these cells are actually NMC or some other chemistry.

I would get them on the phone ASAP and not charge these until they can explain. If they give you a run around I would gladly talk to them for you.

Matt Foley

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

On Tuesday, September 13, 2022 at 06:35:17 PM EDT, James Jones <jgjones252@gmail.com> wrote:

Thank you all for the info and suggestions!

Turns out that it wasn't the meter (I checked with two different meters), and the batteries themselves are within spec (no extra cells, etc.): Their documented fully charged voltage is 29.4 volts, and each one currently reads 29.1. Which adds up to what I see on the meter for the whole bank: 58.3. Here are the particular ones I'm using: https://www.lithiumbatterypower.com/collections/marine-batteries/products/24v-75ah-lithium-ion-battery

They haven't even been plugged into a charger yet; they're still in the "partially charged" shipping condition.

So I guess either these batteries have an atypically high voltage, or the Karvin outboard has a unusually low maximum voltage. Or both. :)

And to answer bobkart's question: I'll definitely post info about how it works when I finally launch the boat in, hopefully, a week or two. And yup, I'm near Lake Washington and will probably launch at Magnuson Park.

Thanks again,
Jim

Re: [electricboats] Maximum input voltage for outboard?

That is a decent battery in terms of energy density!

I'm just surprised to see such a high voltage on an LFP battery after sitting for what I'm guessing is many days. The BMS must not draw very much.

I looked more closely at your pictures, and now see what I suspect is a Star Trek reference in your boat's name. (We sometimes call our Nissan Leaf the Shuttle Craft.)

According to SOC tables I have, 54V resting voltage is 99% SOC, and 99.5% SOC comes in at 55.2V. So if you have the option of turning your charger down somewhat, that should alleviate any concern of damaging the Karvin.

Or you could put a small load on the battery for a bit after fully charging to 58.4V. You only need to bleed off half a percent or so of capacity (~20Wh). A 75-ohm, 50-watt resistor would do it in just under half an hour (but would likely get pretty hot).

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Re: [electricboats] Maximum input voltage for outboard?

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Re: [electricboats] Maximum input voltage for outboard?

(Martin's post crossed mine. Agree with those point as well.)

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Re: [electricboats] Maximum input voltage for outboard?

I second Matt's points. You shouldn't see more than 55V for long with 16S LFP after you stop charging. Even a small load will bring it right down. Have you tried connecting it to the motor? I understand not wanting to damage it, but it *should* protect itself and just not function. I also have a 16S LFP battery, and my motor tops out at 60V (ePropulsion). Also, as a test of the meter you're using, see what it says on the output of the charger with no load. If that's over 58.4V, your meter may be reading high.

Hey James, that's a nice looking cat you have there! I considered those Karvin motors for mine. I'd be interested to hear how well they work. And, I'm in the Seattle area too. Wondering if we frequent the same waters (Lake Washington/Union and Puget Sound between Seattle and Everett).

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Re: [electricboats] Maximum input voltage for outboard?

Nice looking boat! I would not put a stepdown converter into it. Can you maybe get a charger that can be set to charge at 55V instead? That will be better for the LFP cells anyway, you don't get much more capacity by charging them higher than that anyway and it will make them last longer if you limit the charge voltage. Also in my experience you can run motors at slightly higher voltages without damaging them - just don't run at full speed when the batteries are fully charged - it will very quickly go below the 55V as soon as you start powering the motor, I would guess that within the first 10min or so they will be down under 55V.

On Tue, Sep 13, 2022 at 7:55 PM James Jones <jgjones252@gmail.com> wrote:

Hi all,
I've just completed building an electric-powered boat, and upon wiring up the batteries found that the voltage at the end of the line (electric outboard power plug) is higher than expected.
My battery bank is four (4) 24v / 75 Ah lithium ion (LiFePO) batteries, wired with two pairs of batts each wired in parallel, and then series connecting the pairs, which should produce a nominal 48 volts output. The meter however reads 58.3 volts, which is higher than the combined "fully charged" voltage "should"(?) be. Since my outboard (Karvin 6800) has a maximum input voltage of 55 volts, this creates a puzzle. Am I missing something? Do I need to add a component to reduce the output voltage of the batteries? Etc...

Any advice much appreciated,
Jim

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Re: [electricboats] Maximum input voltage for outboard?

58.4 is a fully charged lifpo4 48v system (16s) I would be pretty surprised if you had anything other than 16s or your case two 24v (8s) in series.

I don't have any specific knowledge of that motor but I would also be surprised if it was not designed to work with lifepo4 16s.

Maybe your meter is faulty? maybe there was miscommunication?

What does concern me is the 58.3 volts. It should only be at that high of a voltage when charging and only for a short period. Resting voltage should be around 53-54 volts.

Matt Foley

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466