DC to DC Charge Controller for Lithium Batteries

[TheHubbardBus]

Originally Posted by Meathead

I bought the Renogy DCDC unit and I am very happy with it. It has dip switches that you set for your battery type and you wire it to your ignition switch so it’s only on when you are running.

Does that have the ability to charge your starter batteries from your house bank? That's one thing I wish the Victron unit did have, and am actually surprised it doesn't (to my knowledge - I haven't really dug into it yet - I could be wrong).

One thing I do like about the Victron unit (which may be standard for others) is its ability to run in power supply mode. I plan on taking our house batteries out and store them in the house when not in use, and this allows me to temporarily power a few low-draw DC bits on occassion as well as enabling the AC passthrough functionality of the inverter so we can still use shore power.

John - what are your impressions of the Sterling? I was going to go that route before I settled on the Victron.

[Meathead]

No. HB it doesn’t.

[jackdebear]

No, I did not read beyond the first line of your advice wherein you posited 1C as a reasonable charge rate. There may be batteries designed to bare that rate but not most. I don't read comments on this forum because I've found that the membership generally not worth the time. I will ask in response - is there anything in my advice to the question that you would take exception to? All I said was consult the mfg. I think that's solid advice and I stand by it.

[TheHubbardBus]

Originally Posted by jackdebear

No, I did not read beyond the first line of your advice wherein you posited 1C as a reasonable charge rate. There may be batteries designed to bare that rate but not most. I don't read comments on this forum because I've found that the membership generally not worth the time. I will ask in response - is there anything in my advice to the question that you would take exception to? All I said was consult the mfg. I think that's solid advice and I stand by it.

There's no beyond about it. You simply did not read. For reference, the first line of my 'advice':

Originally Posted by TheHubbardBus

Most lithiums (just the cells) can generally tolerate at least a 1C charging rate.

Do you understand the difference between a battery and a cell? Do you know what he world 'tolerates' means, and how it's different from words like 'optimal', 'suggested', or 'recommended'? How about the word 'generally', particularly when used in the context of litihum cells (LFP) commonly used in mobile power generation scenarios?

But no - aside from rudely misrepresenting what I said because you didn't read any of it - I don't take exception to your advice. You're right when you say most (drop-in) batteries don't accept a 1C charge rate (usually a function of their BMS). And you're right insinuating that 1C isn't optimal regarding longevity even when they do (I think you used the words 'doesn't like'). And of course you're right in advising one to consult the manufacturer's documentation. None of this was in dispute.

[jackdebear]

Lithium may "tolerate" high rates of charge and discharge but you won't be doing them any favours. One of the reasons to spend the extra $ on them is the payback in longevity. If that's an advantage that interests you be moderate in the rates at which you charge and discharge them. Your batteries, your business. Just saying.

[TheHubbardBus]

What you're just saying is the same thing more than one person here has already said, myself included. Once again we're in agreement.

[TheHubbardBus]

Originally Posted by Meathead

No. HB it doesn’t.

Gotcha. I saw someone on YT the other day saying they came out with one that did. Guess that's a recent addition or a different model (or they were wrong).

[john61ct]

Assuming not drop-ins

If the bank is set up and cared for so that it will last 6000 cycles, EOL defined as 75% SoH

at a 0.4C max charge rate

and just that one factor out of dozens is changed to occasionally charge at 1C or even 2C when fast charging is required by the use case, say 10% of charge cycles

then lifespan may be reduced to say 5,500 cycles instead.

Up to you if you think such a trade-off is worthwhile

For me I say yes, NBD.

Note that is only 14 years of dajly use
and in fact there are hundreds of LFP banks at 18 years now, nowhere near 80-85% SoH.

[john61ct]

Note also talking only high quality cells bought through known-good suppliers, Grade A new and decently matched

likes of Winston, CALB, GBS, Sinopoly, CATL and A123 / LithiumWerks

not cheap stuff from random chinese vendors, likely lower grade factory rejects

[jackdebear]

If we're in agreement why are you giving me grief? I read the odd question on this site if I think I might have something to offer or gain from it. I've taken trouble to learn 'what I need to know' about lithium. And I've seen other people offer the advice that it was a good idea to charge them at 1C. You were the first to answer this dude and that's what I saw in the first sentence of your advice. That's what I sought to clarify for the person asking the question. Just assumed he was starting form zero and could possibly be lead to engage in battery maintenance that was against all the main stream advice. "Tolerate"? I guess a person could 'tolerate' drinking themselves into a coma periodically. I wouldn't recommend it. Even periodically. Please just let this drop now. It's getting tiresome and I'm signing out of this thread.

[john61ct]

That's fine, but ideally you should quote so people can see who you are kvetching to without having to navigate upthread to figure it out.

Open forums are like this, best to take what is useful, and then just ignore posts (and posters) you're unhappy about.

[jch511]

Originally Posted by john61ct

That's fine, but ideally you should quote so people can see who you are kvetching to without having to navigate upthread to figure it out.

Open forums are like this, best to take what is useful, and then just ignore posts (and posters) you're unhappy about.

Originally Posted by jch511

So I have a new question concerning charging my Lithium battery. I bought an isolator to use the engine alternator to help charge my battery, then realized upon reading more that I should instead use a DC to DC charger for Lithium batteries; so I returned the isolator and having read that the DC to DC charger is rated in amps (unlike the isolator), I'm wondering what size to get. My intent is to use it for a 300Ah Lithium battery, charged not only by solar panels (total optimum of 1260 watts), but also by the DC to DC charger. I've read that you don't want to pump a bunch of amps into a Lithium battery when charging, so now I'm wondering what size DC to DC charger to get (and how do you figure that?), and does anybody have a recommendation as to vendor?

Thanks!
Jim

~~~~~~~~~~~~
Thank you all for your responses. What I've learned is that I should have researched the electronics of these systems more than I have, although I wonder how many of you were also novices when you started down this road of building a skoolie. I've been a scientist all my professional life (now retired) and have worked on oceanographic buoys that are powered by solar cells, but I never had to get into the nitty-gritty of lithium batteries and charge controllers so much as I am doing now, which is great! I just need to back up about 15 steps and realize that I've spent money where I probably shouldn't have, and do the best that I can with what I have.

So, it appears I've installed way more solar panels (6) with more wattage (210 each, 12.3 amps, 12 volts) than most people, and that my one lithium battery (300Ah) is probably sufficient if I'm careful about how I use a DC to DC charger (18 amps) (mainly, when the engine is running, but don't burn out the alternator), and that my 40 amp charge controller (I made a mistake in my first post by saying it was 80 amps) is not going to do the trick, unless I buy another and use in parallel, or replace that one with a 100 amp controller and sell (gift?) my old one (I can't return it, and it's never been used), and that the brand I had (Newpowa) doesn't show everything it should on the display. I also learned, by the way, that attaching my own MC4 connectors to my solar cabling is not so easy as it appeared (must use special MC4 crimpers, if you plan on doing it a lot, and I see I'm going to).

So despite my embarrassment at being such a novice, this thread has led to my learning a great deal, so THANK YOU! (And sorry for some apparent disgruntlement among some.)

Jim

[john61ct]

As to your panelage, if living off grid best approach is every possible sq ft is utilised.

1200W is decent, figure at least 500Ah per day produced

An 800+ Ah bank would capture more of that, depending on insolation conditions, and how much your concurrent daytime loads divert going into storage.

With only 300Ah, you will with good insolation produce a lot of "excess" energy, may consider shedding / diversion / opportunity loads,

storing some of that energy as hot water in an insulated tank, running a crockpot, dehumidifier or freezing ice for coolers

If you wanted to actually store more of your panel input as electricity then go bigger on storage. This will give you more cloudy days' buffer, usually good to shoot for at least 3 days if "mostly solar" is the goal.

[TaliaDPerkins]

When I see a battery with an internal BMS and a 1C charge acceptance specified, I expect it to meet specified life cycle charge/discharge count when operated at that rate -- certainly if I am telling the inverter to hold it within 10% to 90% charge/discharge as allowed extremes, and more usually 20% to 80%.


Thoughts on the plausibility of that?


I am employing LiFePo4.

[Rucker]

Originally Posted by TomDPerkins

When I see a battery with an internal BMS and a 1C charge acceptance specified, I expect it to meet specified life cycle charge/discharge count when operated at that rate -- certainly if I am telling the inverter to hold it within 10% to 90% charge/discharge as allowed extremes, and more usually 20% to 80%.

Thoughts on the plausibility of that?

I am employing LiFePo4.

A quick review of the available literature on line suggests you are correct. Empirical studies are few, so we have to rely on the manufacturer's spec, no doubt based on some reasonable amount of testing.

[john61ct]

Yes if you are talking the usual "2000-4000" cycles predicted, I am pretty sure you'll get that.

But IMO that's a pretty low bar.

Top quality cells from the likes of Winston, CALB, GBS, Sinopoly, CATL and A123 (now Lithium Werks) IMO can hit 10,000 and more treated well.

Of course cycle lifespan means little without an EoL spec, mine is 70% EoL

[TaliaDPerkins]

Originally Posted by john61ct

Yes if you are talking the usual "2000-4000" cycles predicted, I am pretty sure you'll get that.

But IMO that's a pretty low bar.

Top quality cells from the likes of Winston, CALB, GBS, Sinopoly, CATL and A123 (now Lithium Werks) IMO can hit 10,000 and more treated well.

Of course cycle lifespan means little without an EoL spec, mine is 70% EoL

I'm talking the spec'ed cycle count of 4000. What you are calling a "low bar" is about 11 years of daily full cycling, when with the solar capacity I have I should expect instead to only rarely pull from the batteries in the day and instead lightly pull from them the overnight.


Batteries are a consumable with a long lifetime, no sense in trying to stretch over your own lifetime.

[john61ct]

I don't get that, at all.

LTO lasts ten times longer all things being equal.

Why wouldn't you want a bank that lasts longer than your house, gets passed down multiple generations?

I mean I know many solar users aren't environmentalists, but...

[TaliaDPerkins]

Originally Posted by john61ct

I don't get that, at all.

LTO lasts ten times longer all things being equal.

Why wouldn't you want a bank that lasts longer than your house, gets passed down multiple generations?

I mean I know many solar users aren't environmentalists, but...

"LTO lasts ten times longer all things being equal." <-- No,5X.



The size of a battery bank which gives double a "usual" cycle count of say 8000 cycles while giving full electric even just 1 day capacity is very large. There is an upfront cost to carry those around, there is an opportunity cost to carrying them around (fuel cost) and the upfront cost to buy them.


After the nominal 11 year at minimum of 4000 cycles, especially if you are already carrying enough solar panel capacity to use up these cycles more likely at 15 years, then you need to replace them...


...And you get to replace them with what better batteries are available in 15 years.



LTO at the capacity I am thinking of costs about $50k. Are you trolling me thinking anyone should be nostalgic about a battery pack? As is, LiFePo4 for the same lifetime by replacement if 60% at most of that cost.


"Environentalism" has nothing to do with it one way or the other.

[Rock-N-Ruth]

Originally Posted by jch511

Okay, I'm in over my head. You guys are probably giving me great advice, but only one problem: I'm not an electrician and/or don't have that much experience yet, so I'll keep studying. I couldn't even find what a "Sterling, BB series" even is!

But I did glean some good advice from the thread which gives me more to study and think about. Mainly, it does not appear that I need to buy a DC to DC converter at a high amperage output if I'm not using that much power in my system at a high rate.

I've still got a LONG way to go on this build-out, so hopefully I'll learn what I need to throughout the coming months (hopefully without spending too much more than I have to).

THANKS everybody!

You might find this video useful.
https://youtu.be/jgoIocPgOug