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Old 12-15-2021, 04:39 PM   #1
ShrimpBurrito
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Default Converter with adjustable charge current?

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
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Old 12-15-2021, 06:14 PM   #2
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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.

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Old 12-15-2021, 09:01 PM   #3
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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
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Old 12-16-2021, 10:15 AM   #4
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Default As the self-proclaimed TM "LFP" expert ...

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.
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TM='06 2619 w/5K axle, 15" Maxxis "E" tires. Plumbing protector. 630 watts solar. 450AH LiFePO4 batteries, 3500 watt inverter. CR-1110 E-F/S fridge (compressor).
TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 12-16-2021, 03:13 PM   #5
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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
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Old 12-17-2021, 10:22 AM   #6
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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

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Old 12-18-2021, 11:08 AM   #7
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Default Long and Complex, sorry.

Quote:
Originally Posted by Bill View Post
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.
Answer #1: LFP internal battery resistance is very low, but possibly unequal (between parallel batteries) by small amounts. The BMS itself is typically contributing more resistance than the cells themselves. The State-of-Charge in battery battery packs will eventually equalize, when one approaches 100% charge before the other (because the Charge State versus Voltage curve becomes non-linear as SOC rises, and the less-charged battery will be favored).

There is definitely a risk of unequal charging among parallel batteries, and it is pretty much guaranteed to happen if the resistance on the charging path through one battery (the resistance of battery-specific "+" and "-" leads from the "bus" connections + and -) ever becomes significantly different from the resistance on the path through the other battery. Even if those leads are the same length and same size, that could maybe happen from a loosening terminal. And any internal failure of ONE battery (though very unlikely with BattleBorn batteries, or my "home-built battery packs) will definitely cause the other to be charged with excessive current, if excessive charging current is ever applied.

It is also possible, for a short period, when one battery has reached "balancing" voltage start and the other (although configured to trip over to "balancing" at the same voltage), has not yet reached that internal Voltage on all its internal cells or strings. This would also cause nearly all available charging current to be directed into only one battery.
- - -
Answer #2: Nearly all BMS units do not provide any kind of active "current limiter" for bulk charging. When charging occurs, it only has a choice between 3 connection states (state-1, fully connected for charging at up to maximum allowed current; state-2, connected to only drive an internal 'balancing circuit', which sends very small amounts of current down the balancing wires; or state 3, charger "input" disconnected, due to reaching Voltage or Current limits for state-1 or State-2).

In the previous post I was explaining that some BMS units do not auto-recover gracefully from temporary over-current situations - requiring intervention on a command interface (a cellphone 'controller', computer interface controller program, a physical 'reset' button, or a disconnect-reconnect procedure (in my brand of BMS, 'Daly' (also called Dahlgreen on some labels), 30/30/30 disconnecting and then reconnecting the balancing wires header performs a physical reset.

The biggest worry in all of this would be: In cases of extreme over-current, the actual circuitry might "fry" before detecting that excess current is present.
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TM='06 2619 w/5K axle, 15" Maxxis "E" tires. Plumbing protector. 630 watts solar. 450AH LiFePO4 batteries, 3500 watt inverter. CR-1110 E-F/S fridge (compressor).
TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 12-18-2021, 11:17 AM   #8
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Question Hmm. it sounds like *I* missed something.

Quote:
Originally Posted by ShrimpBurrito View Post
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.
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TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 12-18-2021, 11:34 AM   #9
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Lightbulb BY the Way - I set my PD charger for "AGM", rather than "Lthium".charge

Even with PD, the charging Voltage in "Lithium mode" (14.6V) is a little high for LFP battery cells. In my slightly old model, The "Lithium" profile charges at 14.6V ALL THE TIME. At a slight cost (the need for slightly longer charging times), I have chosen to set the PD Converter Section to its "AGM" profile.

The "AGM" profile charges at a lower "Boost Voltage", and then drops to a lower but sufficient "Float Voltage" after a slightly-too-short time. But, when I'm in a hurry, for some unusual reason, I can always whack the "Charge Wizard Remote Pendant" button to force it back into another boost cycle. I've never actually bothered to do that, except for testing.

AGM is the correct "alternate" choice, because it doesn't have any LFP battery-killing "equalize" stages set into the profile.
- - -
The BMS in each of my two LFP batteries is allowed to accept the entire output of the PD, with the limit raised to 65A on each battery.
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TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 12-19-2021, 01:07 PM   #10
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Thanks for the feedback, Rick, super helpful!. I hadn't considered unbalanced charging with batteries in parallel to the extent it might trip the BMS. I think your approach of not charging a parallel battery bank at a current that exceeds the individual charge current rating of any one of the batteries is a good idea. So in my case, that means certainly not to exceed 50A, but a bit under that to give a margin to avoid tripping the BMS.

I'm not at all fixated on the AIMS converter. I just found it through a 5-min search on converters with adjustable outputs. But given this discussion, I'm thinking an adjustable output is less of an issue, and makes me more want to consider the reputable PD units like the PD 4635VL or PD 4645VL. I'm more leaning towards the 35A unit -- that's plenty, I think, especially in combination with 300W of solar.

One issue I'm now facing has to do with finding suitable circuit protection between the panels and controller. 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, even ATL fuses. Larger fuses like class T are rated for higher voltages, but I can't find a fuse small enough.....probably around 15A. Seems like it would be a pretty common problem for larger RV installs, and I think it is typically addressed with DIN-mount breakers. Those require a box though, and I was just trying to get away with a smaller footprint.

Dave
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