Putting first system together

[Inq720]

First post, but I have been doing a lot of reading on the forum and watching Will's videos to educate myself. I want to put together my first system for my small sailboat. This is merely to replace two deep cycle lead acid batteries (one to start motor, one house). I'll try to primarily run everything off 12VDC like lighting, marine electronics (chart plotter, eventual radar, sonar, etc) and a small fridge will be the largest user. I will get a sine-wave inverter in the 1200W range, but really have no regular use planned for it. It'll be for things like charging laptops and maybe a blender.

I've been reading about the other components needed - controller, BMS, inverter.
The high-lights, so far...

• ~270 Ah / 12 V set of batteries - looking to order through Michael on the group buy thread.
• Overkill Solar BMS that Will suggests
• (2) 100 W Rich solar panels that Will suggests

For this post, I wanted to get feedback on the charge controller. On another forum (for my boat) charge controllers were brought up and saying how most are a problem for RF interference for marine VHF radios. One post said to look for FCC class B certification and suggested the following (product brand). I also did a search with FCC class B certification and got very few other manufacturers, but with products that appear to be over $1K and I'm assuming for a lot bigger system than what I'm proposing.

Does anyone have any suggestions for smaller controllers that will handle this system?

I also would like to replace both batteries with this one-battery system, but want to be able to start the gas motor and be charged by the motor's alternator (20 Amp). Is this a matter of different circuitry or just running it into the same charge controller. Will has a suggested system that will do this, but I'm not sure I understand all the nuances. I also can't seem to find anything about the VHF interference on this controller.

Thanks all.

 

[snoobler]

LFP can't handle typical currents required for engine starting. The BMS generally limits them to currents below those needed for starting. The current need to start what is anticipated to be a small engine may fall within what an LFP can handle, but you'd have to determine that for yourself.

Recommend you keep one AGM for starting and replace house AGM with LFP.

Problem with charging LFP from an alternator is they can handle LOTS of current for extended periods of time provided they need to be charged significantly. They will run an alternator at max and shorten the life of the alternator. There are DC-DC converters and other devices designed to limit this. Given that your alternator is only 20A, there are few options that would reduce that as most are designed for reducing current from much more powerful alternators.

In your case, I would recommend:

LiFePO4 Battery Isolation Manager (BIM)

LiFePO4 Battery Isolation Manager (also known as the BIM) monitors voltage and connects and disconnects batteries when needed. Click here to read more!

battlebornbatteries.com

This will cycle the charging on for 15 minutes and off for 20 minutes to give the alternator a break.

Lastly, while I find no evidence of FCC Class B certification, Victron products are extremely popular with marine craft, so I would expect their charge controllers do no harm.

 

[Inq720]

Thank you for your help. I'd read that hooking up an alternator to LFP might ask too much of the alternator and I've burned a few rectifiers trying to recharge batteries by driving a car. So, that one I was looking out for. Just didn't know what to call the component I needed to do a search. Thanks for supplying those.

Also, the desire to get rid of the starter battery... was minor desire. In general, I'm assuming, the solar panels will keep my house battery charged; and the alternator will keep the starter battery topped off. Having separate battery systems has a few desirable benefits and only the weight as a disadvantage. I think I'll keep starter battery. Only if I had a failure was having some cross-over necessary... and if so, I can jury-rig that. I could keep the Perko switch going to the motor between them.

However, I didn't even think about the starting current issue with LFP. My thought "was" that my starter battery has 450 CCA and the LFP at only 2C was going to be 560 Amps. Most of the time the motor cranks in a half second. What am I not missing?

In case, I don't need to run the engine for weeks, it might be prudent to have some kind of trickle charger going from the LFP system to the starter battery, but all I've ever seen are 120VAC to 12V trickle chargers. Usually for less than $20.

 

[Inq720]

I think I'll answer my own question... its not the batteries. The BMS is only rated for 120A.

 

[snoobler]

You're missing the BMS limitations. Many are limited to well under 450A, etc.

There are 12V to 13.8VDC converters. They'll take a wide input range and put out a steady 13.8V, which is a good float voltage for AGM. They run about $50 on Amazon. Your house batteries charged on solar can keep your starter battery floated. Will probably draw about 5W max during float.

 

[Inq720]

Cool! Something like this? $19

https://www.amazon.com/Converter-13-8V-Automatic-Waterproof-Transformer/dp/B07X9Y5MXT

 

[snoobler]

For me, that particular item 12V to 13.8V is $31.99, and yes. That would work.

 

[Inq720]

I got back an email on the controller above, but didn't really answer my questions.

I read somewhere that Tesla cars can be programmed to not fully charge. Don't recall what numbers are typically used (95% etc) but will make the battery last a lot longer.

With 270 Ah, I have way more power than I think I'll need and so I was wanting to reduce that top charge cutoff. Is that typically done with the charge controller or the BMS? The controller company doesn't seem to have the facility to do that. I see that Will's suggested BMS is programmable. Will it let me set this... and is it something I could easily do. Sometimes I might want to top it off... others go far less.

 

[snoobler]

Once you have the BMS configured you'll figure out a different charging scheme to only hit 80-90% or whatever works for you. You'll change it by changing the peak charge voltage.