LiFePro4 discharge question

[Cpt Mark]

Been researching and reading all about these battery systems. I read Maine Sails excellent article and then handed it over to a buddy who is an electrical engineer as it was over my head. I did get a lot out of it and he filled in more.

In looking at various batteries I see 100AH batteries rated for anything from 50AH -100AH discharge with some able to have a max discharge of 350 AH for 3.5 seconds.

Per manuals my windlass draws 150 amps and my electric winch draws 200 amps. Both of these are above 100 AH discharge. Yet other boats are doing this without issue. Is the reason why as simple as you have 400AH battery capacity so a large draw is spread out across all of them? Am I missing something else?

I have a catamaran, 2 engines and a 4KW genset. Also thinking to simplify things maybe not using the alternators at all. Thoughts on this? I can put up quite a bit of solar which is the plan.

[Knot Safety]

We have 400ah lithium (2x200) plus individual start batteries on our catamaran. 900w solar and wind generator.

We never need to use the engines to charge and we do well for power. Two fridges Various electronic gadgets. Anchor lights. Fans. All run at various times through the night and we wake up at about 13.18 volts on the batteries. Normally fully charged again by around noon.

We run our anchor winch only with the engines running. Sail winches are also electric and they do just fine.

[Flod]

Normally lifepo4 can take up to 3 times the capacity in shorter discharge. This means you can get 1200A out of your bank in shorter periods theoretically. A load of 150-200A is not going to be any problem. And you don’t run these devices for any longer periods and at full rated output. I have 200AH bank and I don’t even see a drop in voltage when putting the load of my 1,5 kw lofrans in action. Make sure to have correctly dimension on cables and fuses and then your good to go in my opinion

[GRIT]

If you see a 100 AH battery, with a maximum discharge of 50 amps. It's usually because the BMS can't handle more. These are sold as "drop-in" battery systems. Some are supposed to be quite good, others... not so much.

If you buy cells, and turn them into a battery, with a separate bms, where the bms is there to actuate solenoids, for cell protection (High or low voltage protection), then you can draw much more out of your "battery" than 100A.

The ready made batteries are the ones with more severe limitations. Raw cells, connected into a battery, can output much more power.

We purchased cells, and made a large, 720 AH battery with them. I can't speak to the ready made ones, but the type we have can easily output 1400 Amps.

Good luck, and be careful with your purchase. Lithium is definitely something you want to research, before buying whatever "deal" comes along.

Good luck.
Paul.

[Cpt Mark]

Originally Posted by GRIT

We purchased cells, and made a large, 720 AH battery with them. I can't speak to the ready made ones, but the type we have can easily output 1400 Amps.

Good luck, and be careful with your purchase. Lithium is definitely something you want to research, before buying whatever "deal" comes along.

Good luck.
Paul.

How difficult was it tom make your battery?

[Flod]

Not very difficult. See for example

https://shop.gwl.eu for some instructions. You basically buy the cells you want or one of the “packages” where you get connections etc. If you are somewhat familiar with electricity you should be fine

[GRIT]

The actual build is not difficult, as has been said. But designing does require some thought. There are many ideas on what is the right way to do it.

Care in design and properly setting up voltages is very important. It's not rocket science, but it does require some knowledge.

It's not a cheap modification, so they're probably not worth it, if you're just using your boat on occasion. If you're a live-aboard, they're really nice to have.

We've only had ours for a year now, and only living aboard full time for 6 months. I can say they are impressive, and I'm very happy with my choices, so far.

I have not used the site mentioned above, but I would caution you about vendors that claim "anyone" can build a lithium battery system. It is a system, not just a battery.

If you think I can help, just ask.

Cheers, and good luck.

Paul.

[Cpt Mark]

Originally Posted by GRIT

If you think I can help, just ask.

Cheers, and good luck.

Paul.

Hi Paul,

Watched a few you tubes on how to build your own 400 watt solar system including LiFePro4 batteries. Ok, doesn't look that hard and would certainly fit my budget better. Less $ than time.

I'm also willing to be talked out of this idea if it's a bad one.

Relion makes a LiFePro4 battery they claim is a dual purpose. Use one battery (bank) for both house and start. Interesting idea.

I found these cells which can handle a much larger discharge current and have solid connections.

https://www.amazon.com/dp/B0867D5KX7...language=en_US

This is the same companies BMS

https://www.amazon.com/LifePo4-Manag...language=en_US

I also want to put solar hot water under the panels.

What I don't see available is a case to put your batteries in.

My application would be a 300-400 AH battery bank. If it could be used as the engine starts that would be ideal. Expect 1200 watts solar. Have 4K generator as backup with a Sterling 50amp battery charger capable if LIFePro4 batteries. Thinking of not using the alternators to keep things simple.

I have a windlass (150 amps) and an electric winch (200 amps). Microwave, computers, tools. All lighting LED. Some of the cruising I've done requires a lot of trial and error to anchor to find a place to hook. Shale rock below. Might have to raise/lower the anchor 10 times. I have a chain counter and do it solo from the helm. Also have a single portable induction plate. If I could lose the propane inside the boat that would be great. I'd still have propane for the bbq but would have the option of much less fills this way and propane fittings by country is a PITA.

Will be full time liveaboard out cruising this summer and beyond. Where remains to be seen because of Covid19 but I'm on the west coast of the U.S. so I can float around here until things settle down.

Thanks for any help you can provide.

Mark

[smac999]

to aswer the question. yes if you have more batteries in the same bank. the load is spread between the batteries.

so 4 batteries rated at max 50a should be able to power a 200a load. it may be more like 55a, 50,50, 45a from each battery depending on wiring. so best to leave some leeway in there when designing.