AC battery charger for AGM start battery and Lithium bank

[john61ct]

Originally Posted by SteveWrightNZ

this is more mad scientist territory and not fit for public consumption, unless you like lots of smoke coming out of things.

Yes, so best to segregate into its own thread for mad scientists?

[Unregistered-1]

Originally Posted by john61ct

Yes, so best to segregate into its own thread for mad scientists?

Since you are ASKing, no. I'll put it where I deem fit.

My point is, those who can, do. Those who cannot, probably shouldn't.

If you have the knowledge and skills, wind that transformer and smile. If you do not have the knowledge and skills, wind that transformer and burn.

Do what you want.

[Harryg]

I have a similar Lithium/AGM setup on my 13m cat with BMS and switch panels designed and supplied by Outback Marine, Australia. I have a Mastervolt Combi (12/2500) inverter/charger which is fine, but the Victron is a better match for the OM system. OM has a considerable amount of info on their website - worth a look.

[CatNewBee]

Nothing will burn, as long as the transformer and the rectifier can output more Watt than the solar controller can handle. What than happens is, the controller just limits the input / output at high voltage and does not even think about seeking a better output by shorting the input.

[Unregistered-1]

Originally Posted by CatNewBee

Nothing will burn, as long as the transformer and the rectifier can output more Watt than the solar controller can handle. What than happens is, the controller just limits the input / output at high voltage and does not even think about seeking a better output by shorting the input.

I did wonder if the controller would limit the current.

For all the simplicity, jury-rigged, and second-hand parts nature of the thing, it works amazingly well. My (smaller) generator is only 650watts, and that is nowhere near the 45A (28V) capacity of the MPPT controller. It's fascinating to watch the poor little generator at the whim, beck, and command of the MPPT controller - which fully does some very bad things said poor little genny!!

If I recall correctly, I was seeing about 35A into the 28V battery system from the 650W genset.

I'd be wanting to stand a long way back trying this trick on rectified mains however.

[CatNewBee]

35A x 28V = 9

Originally Posted by SteveWrightNZ

I did wonder if the controller would limit the current.

For all the simplicity, jury-rigged, and second-hand parts nature of the thing, it works amazingly well. My (smaller) generator is only 650watts, and that is nowhere near the 45A (28V) capacity of the MPPT controller. It's fascinating to watch the poor little generator at the whim, beck, and command of the MPPT controller - which fully does some very bad things said poor little genny!!

If I recall correctly, I was seeing about 35A into the 28V battery system from the 650W genset.

I'd be wanting to stand a long way back trying this trick on rectified mains however.

35A x 28V = 980W, this is far beyond 650W (+50%).

Either you have a 1000W genny or something is wrong with his protection circuits...

Anyway, nice output.

[Unregistered-1]

Originally Posted by CatNewBee

35A x 28V = 935A x 28V = 980W, this is far beyond 650W (+50%).

Either you have a 1000W genny or something is wrong with his protection circuits...

Yup. 650W genny not very happy.

[exMaggieDrum]

Originally Posted by SteveWrightNZ

For "mains" charging from my 230V generator, I used a transformer to step down to around 100v, then bridge rectifier to 150V DC, then connected the DC directly to my solar MPPT charger input. Wow did that make that generator grunt!! Topped that battery up real damn quick!

Since you already have a quality "charger", I'd look at making some interface from the mains to the solar input.

The size and turns of the transformer would be critical, as the MPPT controller WILL gear itself up and down and look for maximum "juice" from the (near-zero impedance) mains via this transformer. In effect, the MPPT charger will go into "can we kill this transformer" mode - should be hilarious to watch, it certainly was when it was on the generator!

Should probably add, that this is more mad scientist territory and not fit for public consumption, unless you like lots of smoke coming out of things.

I wouldn't do what you suggest although it is creative. If I were to think about it I would certainly look at the specs of the solar charger to see what limits it has for voltage input. I don't think mine would take 100v. And I like the redundancy of my different chargers. Just my preference.


And - I do look at the BMS as a safety device, at least as far as the safety of the battery goes. If I were to forget and leave a charge source on it would be the solar. It could overcharge it in one day's outing to town on the dink. And then crispy-fried battery. Or, I could leave some big draw on and suck it's life out.



I believe most BMS's also cell balance. I still am not totally sure that is a necessary feature. Some say it is beneficial and some say potentially destructive. But if it works, it only balances the cell packs in parallel that are then in series to make "12" volts. So each individual cell is not balanced in any case. I have 16 cells to make 400ah and my HousePower BMS will only monitor and balance each set of 4 that are paralleled to make 400ah at 3.2v. At least that is what I understand.

[CatNewBee]

Balancing is important to get most possible energy out of the pack. If you not balance, the first ( highest cell ) will stop charging (disconnecting the charge sources) while the rest is lets say at 50%. Then you discharge (half capacity) until the lowest cell hits the bottom. Then the BMS stops discharging, the other cells especially the highes have 50% remaining energy. You just degrade your battery. Some cells stay all the time near 100% SOC, some stay bellow 50%, both is not healthy, and you use only half of the possible capacity. I guess, you get the point.

Balanced (equal charged cells) provide most usable energy between stop charge and stop discharge, also they age together at the same pace. This is what you want.

Anything else are fairy tales from guys with theoretical knowledge, but no practical use.

[CatNewBee]

Passive balancing just burns part of the charging energy on a single cell, to slow down the charge while the other cell accumulate the whole current.

Active top balancing recuperates this energy and feeds it back at the bank. There is then less heat and faster charging.

Active bottom balancing takas care of the deepest discharged cell, that is charged by using energy from the other cells, so the low cell is not standing at LOW SOC for a extended time, also the total usable capacity of you bank is improved.

Mid balancing happens based on maximum allowed cell difference. It takes place if something really wents wrong. It tries to re-sync the cells to an acceptable state, this happens by disconnecting charge and load bus and trying to resque the battery. It is an emergency program you wont experience during normal operation.

You cant do that efficiently manually by no means. If the cells are in balance, no balancing will occure anyway, if they are not - better the BMS reacts on it instead of waiting until a human notice it and takes measures.

[john61ct]

Many LFP users have no active balancing at all, and those I respect most, marine professionals with experience with hundreds of installed LFP systems

actually **disconnect** that functionality from their own personal systems costing thousands.

Dozens of users with long experience have reported harm caused by having per-cell gadgetry installed in daily use.

And hundreds regularly report no problems with this approach.

Manually checking cell balance weekly, then monthly is a good start, but most consider that overkill and move to quarterly or even longer.

Even years of careful usage - and that includes avoiding both high and low voltage shoulders, keeping well below 3.5Vpc in daily use - have resulted in systems that have **never** needed even manual re-balancing.

I am not advocating "no cell-level gadgets" myself, but feel pretty strongly that this bit here

Originally Posted by CatNewBee

Anything else are fairy tales from guys with theoretical knowledge, but no practical use.

shows an ignorant bias toward the path that **you** have chosen.

[CatNewBee]

Well, there are batteries from bare cells with no bms or having contacts for external BMS, you can buy them, they are much cheaper and do pretty well with up to 1000.. 2000 cycles.

Its your choice.

Cell modules can fail, but more likely humans fail. You are not watching the battery all day long, especially not after 4 years or more of usage. There is no difference in the first place with having a BMS with balancers vs. keeping the cells at low SOC.

Regular BMS will do nothing to the battery at this levels, it wont flip alarms, it will not balance.
If you not instal it you simply lose a second line of protection when you fail. Some believe they never fail. And if they do, there is no one else to blame, so they stay quiet.

I chose my system, because I am convinced it fits my use pattern and knowledge, so I can handle it even if it fails. Nothing is perfect. I do not say, everyboby should use it, there are simpler solutions around. But I would strongly recommend to use a BMS with LFP that matches your capacity and use pattern. It would be stupid to invest a serious amount for cells and not protect the invesment by a decend system.

You can buy an expensive car or vessel an drive/sail with no insurance, and hundreds do it around the world with no incidents. But if you cannot afford a replacement out of your pocket youll buy an insurance. Same for a BMS...

[exMaggieDrum]

Excellent examples of why this is an interesting issue for poor slobs like me.


I top balanced my cells very carefully over a 10 period when I got them. Interesting that I had exactly the same voltage for each cell to stat as I did at the end to the thousandth of a volt only at a higher voltage.



So I understand the issue if you have one cell out of balance with another cell, just like you would have with FLA batteries as well. We have all seen FLA batteries that have one or two cells go out over time if they have not been maintained well. Working as a marine electrician it was common, usually from poor practices by the owner/operator. I never had it happen on my boats but batteries can vary. So I get that.


The issue, for me, is whether this really happens in practice with proper maintenance and usage of LFP batteries. Some say yes and other say no. Some think balancing is absolutely mandatory and others say don't do it as it is completely unnecessary.


It is easy to say to check the voltage on each cell frequently, whether weekly (I hope no one does this because if it is necessary then I am going to toss my batteries as soon as practical), or less frequently like quarterly or monthly.


However this is actually a hazardous operation as the connecting straps from each cell has to be disconnected, from one end at least, and for 16 cells there is great opportunity to drop a wrench over the post bolts or other straps and have a major "situation", or just misplace the loose strap and have the same problem. It is also a very labor intensive process also involving removing the framing and hold downs for the cells, which may be harder or easier depending on how this is designed and installed. Then every connection has to be retorqued and the hold downs put back on.



So it is very much like the situation where "if it is too hard or too hazardous it is not done as regularly as might be best". I replaced FLA Rolls batteries in good shape on a previous boat simply because in the space I had it was very difficult to inspect and add water to one 6v battery bank.



So I have to balance the difference issues here (no pun intended). It is a risk vs. reward problem. Of the issues, shorting the cells out with a misplaced or dropped tool is major for me. I use shorty wrenches and sockets when working around batteries but they invariably get little arc marks on them over the years. I have put insulation on them to help prevent accidents. Others may be better at this then I am but better electricians/mechanics than me do this.


So what is the evidence, in the real world, that cells get out of balance to the degree it is important, and, is there any evidence that proper practices will prevent that from happening? I certainly would prefer to check cell balances on a less frequent period.


Cheers

[john61ct]

Originally Posted by CatNewBee

Well, there are batteries from bare cells with no bms or having contacts for external BMS, you can buy them, they are much cheaper and do pretty well with up to 1000.. 2000 cycles

Or 5-8000, maybe longer when charged properly as above. We just don't know yet, few have banks over 7-8 years old yet.

2-4000 cycles looks do-able even for those following the low end of mfg / gear vendor norms.

[john61ct]

The "BMS functionality" related to pack-level protection is just LVD, OVD and temperature, which last is often missing even from systems costing thousands.

Not saying DIY for these is for average boaters to take on, but for those willing to put in the research and testing time, it isn't rocket science either.

Again, I'm not advocating that approach, but think blanket dismissal of it is not warranted.