Converter with adjustable charge current?

**ShrimpBurrito** · 12-15-2021, 04:39 PM

My Trojan T-125s are at the end of their life, at about 6 years old, and while they've served valiantly, the prospect of almost double the power in a package that is the same size and less than half the weight has always been attractive to me. So when Battle Born had a "blemish" sale last month, and those batteries being a qualifying expense for the federal solar tax credit (I think), I sprang for them. I'm going to put up three 100-watt panels in series, which will either be the 12-pound HQST panels, or the 15-pound Renogy Eclipse panels, which have Sunpower cells and thought to possible produce more current. I've bought both to test, and will install the winner.

I also have an old Parallax converter that I don't think will be compatible with the lithium batteries, though admittedly I have not specifically looked at its charge parameters in comparison to the recommended charge profile published by Battle Born (absorption voltage 14.2-14.6, float 13.4-13.8). But, on the assumption it will have to be changed, I have a bit of a dilemma. If I'm going to go through the time, effort, and expense of changing it, I ideally want to take advantage of the high current charge capabilities of the batteries. But my interest in doing that is purely in case I would ever need to use a generator, which I've never had to do with any regularity, but the faster charge profile would occasionally come in handy. So if I could continue to use the Parallax, I probably would, though not at the risk of not providing optimum charge parameters for those pricey batteries.

My bank of 2 batteries will be able to accept a charge current 100 amps, and while I certainly don't need to go that high, even a 50-amp rate would be handy. The problem is that the receptacle I connect the TM to at home is not, shall I say, a robust install, and so isn't equipped to handle much more than a few hundred watts (let's say 500 for extended periods), so I wouldn't really be super comfortable charging at 50 amps.

So -- is anyone familiar with a converter that has an easily adjustable output charge current? I realize it would be an unusual desire.,....I found one, but it's not easily installed in my Parallax bay like the Parallax upgrade kits I see often recommended here on bestconverter.com, nor is the current adjustment feature easily accessible (https://www.amazon.com/AIMS-Power-CO.../dp/B07N1K43NQ).

I know I'm unlikely to find something, but just wanted to make sure I'm not missing something obvious.

Thanks!
Dave

**Bill** · 12-15-2021, 06:14 PM

Would it not be possible to install a better outlet? I don't know the physical layout of your house, of course, but a new run of #12 Romex is often not very hard to do, and would do a lot of good. And a new run of #10 Romex would enable you to install a 30-amp RV outlet. I've done both on several occasions, and I'll volunteer to do it for you next time I'm out your way.

Bill

**ShrimpBurrito** · 12-15-2021, 09:01 PM

I really appreciate the offer, Bill! I thought of that, but the issue is not only the wiring to that receptacle, but also that it’s on the same circuit as one that runs a car charger for a plug-in hybrid, which runs about 10 amps. I don’t want to rely on coordinating plug-in charging and TM charging. I don’t think I can run another circuit because the power all comes from a detached garage, and I think the feed to the garage is maxed out.

It’s an ooold house!

But, please do look me up the next time you’re in LA!

Dave

**rickst29** · 12-16-2021, 10:15 AM

and an occasional installer LFP batteries (INCLUDING Battleborns), I must advise you that the 50A "maximum charging rate" is not advice - it is a hard limit, and reaching it will cause problems. The Battery Management System ("BMS") internal to each of your two batteries will disconnect from charging when that limit is reached, and it might be a bit complicated to re-enable that function.

With my own home-built LFP batteries (not Battleborns), my cheap BMS might be recoverable by "restarting" from the cellphone App - or it might require physical shutdown by disconnecting and reconnecting the battery. My cheap one might even fry an internal circuit, if the overcurrent becomes "too excessive". You DON'T WANT TO FIND OUT the "recovery/reset" procedure for Battleborn's internal BMS (which probably is recoverable, but might involve significant delays or disconnect of the battery leads before automated recovery).

I know that you would like to reduce the generator run time, as much as possible. But, if you charge with "up to 90 Amps", there could be a moment when one battery has gone into "balancing mode" while the other battery is still accepting full charge. A 100A charger with sufficient voltage will happily overdrive the second battery by a larger margin, before it also reaches adequate internal Voltage to switch over to balancing mode. All BMS circuits can be over-driven for a short period of time, but it is too risky to overdrive by such a large amount.

Your alternative is to stay with a "normal" converter section. My own slightly modified "60 Amp" PD Converter actually charges my LFP batteries at a bit more than 60 Amps. 90 Amps would be both "unsafe" and only save 1/3 of the total charging time.

Over at another forum, where a lot of "home-built LFP Battery" people hang out, the Aims charger you're looking at has also had a few reported problems. I have visited AIMS. (Their warehouse and operations are in my home town, as is Dragonfly/BattleBorn). When I last visited their location, they were (and probably still are) merely an import-and-resale company for various Chinese products. At the time of that visit, they had no "repair and refurb" employees. (I ASKED.)

Aside from the initial "replace if it's defective" guarantee, AIMS probably can't offer any assistance with a maybe-repairable problem.

The internal batteries cells, incidentally, do NOT prefer to be charged at their maximum rates.

**ShrimpBurrito** · 12-16-2021, 03:13 PM

Thanks for the feedback, Rick. My 2 batteries will total 200 Ah, and what I'm reading you saying is that a 50A charge rate will be too high -- is that right? Your battery bank is 220Ah, and you charge at 60A.

The Battle Born literature says that each 100Ah battery can be charged at 50A, so if I put them in parallel, I should be able to deliver 100A of current, though I'm only suggesting I go with 50A, so half the rated charge current.

Am I missing something?

Dave

**Bill** · 12-17-2021, 10:22 AM

Rick -

If the batteries are connected in parallel, is there any guarantee that a given charge current will divide equally between the two parallel batteries? I can imagine (but I have no experience) that when you first turn on the charger, small differences in the batteries could result in a large current imbalance, meaning one battery will charge harder than the other. This will even out, of course, as the initially-lower battery comes up to match the other. But in an extreme example, an initial 100-amp charge might divide unequally - say 75 amps/25 amps. Could this be dangerous to the batteries? Will the BMS in each battery take care of it?

I think you are telling me above that the BMS will take care of it, but you seem to attach some caveats to that statement. Will the BMS forcibly reduce the current in the 75-amp battery, down to something acceptable? Or will it simply disconnect the battery that is being charged too fast - in which case, that battery doesn't get charged at all.

I know nothing about LiFePO4 batteries, so you will be educating me.

Thanks

Bill

**rickst29** · 12-18-2021, 11:17 AM

Quote:

Originally Posted by ShrimpBurrito

Thanks for the feedback, Rick. My 2 batteries will total 200 Ah, and what I'm reading you saying is that a 50A charge rate will be too high -- is that right? Your battery bank is 220Ah, and you charge at 60A.

The Battle Born literature says that each 100Ah battery can be charged at 50A, so if I put them in parallel, I should be able to deliver 100A of current, though I'm only suggesting I go with 50A, so half the rated charge current.

Am I missing something?
Dave

Parallel charging will not be exactly balanced, so "100A of Current" would exceed the 50A rating of one battery (and it's BMS) while remaining within that limit on the other.

However, if you're going to use the AIMS at only 50A, on the bus for both batteries, you can't possibly have that problem. But why buy the AIMS, with that limit in place, when you could use a (IMO Superior) PD? I assumed that your goal was to run higher current from the AIMS, and reduce total time-to-charge from a generator.

**ShrimpBurrito** · 12-19-2021, 10:08 PM

Hi Rick,

Thanks for the feedback. As you correctly stated, a fuse current rating determines the load at which the fuse will melt and break the circuit, however, as I understand it, the fuse VOLTAGE rating only comes into play AFTER the fuse melts, and preserves its ability to break the circuit after the fuse melts.

If the circuit voltage is in excess of the fuse voltage rating when the fuse melts, the circuit may not break because the high voltage is able to arc across the melted fuse. This obviously can quickly become a hazard of course, not only because the fuse has now failed to do its job and there is still an over-current scenario, but presumably the arcing itself could also contribute to a fire.

Most low current rated DC fuses and breakers I’ve found are limited to 36 or 48 volts.

Circuit breakers also have voltage ratings for the same reason.

Dave

**Bill** · 12-20-2021, 07:54 AM

Quote:

Originally Posted by ShrimpBurrito

I'm connecting the panels in series, so at around 65V max, the voltage will exceed the rating of most DC breakers and fuses I've found. Larger fuses ... are rated for higher voltages, but I can't find a fuse small enough.....probably around 15A.

Dave -

Re current ratings: You are exactly right, and in agreement with discussions from major fuse manufacturers and suppliers. It is generally recommended that the current rating of a fuse should be 125-150% of the expected max current in the circuit, to avoid nuisance blowing.

It is worth noting that these same articles remind us that a fuse has a max voltage rating, as you noted in #10 above. The max voltage to be encountered in the circuit must be less than the fuse rating, but it is OK to use a fuse that is rated for a much higher voltage. It is also important to use a fuse that has an interruption spec stated in DC current, not AC current. AC is easier to interrupt because the current goes to zero 120 times per second, which helps to extinguish the arc. DC is harder to interrupt because the interruption has to be accomplished by the fuse itself, while handling the entire overload current.

I suggest that you check out a major component supplier such as McMaster-Carr or Digi-Key. The latter site has at least one fuse rated at 10 amps at 100 VDC, and dozens as soon as you go to 15 amps or more.

Bill

**ShrimpBurrito** · 12-20-2021, 11:07 AM

Great idea, Bill, in checking out other component suppliers. I had already checked McMaster, which didn't have anything of interest, but hadn't considered Digi-Key (or Mouser). I prefer a breaker, but I can't find a suitable one that is not ridiculously expensive or isn't surface mount, a fuse will do.

Dave