adjustable output charger mod

[mlt34]

Is there any reason I can't replace the fine tune voltage adjustment potentiometer in my BMSBattery charger with something like this below, mounted in the case, and add a digital voltage readout to the case, to be able to fine tune adjust from 90% to 100% charge without opening up the charger?

I guess the potential danger could be something bumping the pot and causing overcharging, but that's what the readout is for, so it displays instantaneous voltage and the BMS should protect the battery just in case it was accidentally set too high.

http://www.amazon.com/potentiometer-potential-black-control-Knob/dp/B009QFU9H4

http://www.dx.com/p/0-6-led-dc-7-150v-digital-voltmeter-black-300757#.VMHokIqUdkI

 

[amberwolf]

I'm confused: do you mean "controller" in your title, or "charger"?

Certainly no reason not to add the voltage readout, as long as you have a power source for it (dunno about that one but they often require a separate power source from what they are monitoring).

As for the pot, as long as the one you are replacing is the same ohm range, it'll work as a direct replacement. HOwever, if the original is a multiturn pot, you may find it hard to adjsut the new one as precisely as the original. It will also be much easier to accidentally bump it and change the output voltage, and if you're in the process of charging you won't even know utnil it's too late, and the voltage has already risen above your original target voltage.



IF your BMS cuts off you'll be ok, I guess.

 

[knighty]

if you're worried about over voltage

use a pot with a smaller range than the original, so you can;t turn it up too high

of add a resistor inline with it, so limit it's range

 

[mlt34]

I'm confused: do you mean "controller" in your title, or "charger"?

Oops, I meant charger. That's what happens when I type before the morning coffee

 

[mlt34]

Perhaps it would be better to just add a three position switch like the EM3EV chargers. That way I can have a 50%, 90% and 100% charge profile for the three positions. I'm not sure exactly what resistance I'd need for those, but I could hook up a potentiometer to the 50% and 90% pins and dial in the correct resistance using a digital voltmeter for verification. The three position switch would eliminate the need to have a digital voltage readout (as cool as it would be) AND more importantly it eliminates the chance for accidental incorrect voltage selection because there are only three preset options.

 

[mlt34]

I find this unit that can measure voltage and current up to 100V and 10A. http://www.dx.com/p/jtron-0-28-led-4-digital-dual-display-dc-ammeter-voltmeter-red-volt-blue-amp-0-100v-100a-256907

It would be an awesome addition to a charger's case. Only problem is that the LEDs need an input of 5-30V DC. You think there are any 5V places to tap into inside a 54.6V charger? I can put a DC-DC step down converter in there, but at that point I'm really starting to fill this charger with a lot more electronics :lol:

 

[dnmun]

you should be able to get enuff power for the display from the 12V regulator if you have the kingpan type charger. you will need to analyze the circuit to know where to introduce the trimpot and you should use something like a ten turn bournes 3296 type and put it in parallel with the resistor already present or change the current resistor so that the trimpot can function in parallel with the replaced resistor to give you the range you need. too far from the standard voltage may make it hard for the transformer to produce the same amount of power.

 

[d8veh]

Why do you want 90% charge rate? In many cases the balancing happens at 100%, so you'll end up with a knackered battery if you don't fully charge it.

 

[mlt34]

you should be able to get enuff power for the display from the 12V regulator if you have the kingpan type charger. you will need to analyze the circuit to know where to introduce the trimpot and you should use something like a ten turn bournes 3296 type and put it in parallel with the resistor already present or change the current resistor so that the trimpot can function in parallel with the replaced resistor to give you the range you need. too far from the standard voltage may make it hard for the transformer to produce the same amount of power.

I was thinking of replacing the potentiometer that is already there with an exterior one. My thinking was that if I can open the case to make slight adjustments with that pot, why not just modify him to an exterior pot so I can make the adjustment from the outside? But the switch seems like a safer method, since it limits the final output voltage to the predetermined settings.

edit: the switch method meaning a switch connected to a pot on each setting so I could dial in the correct resistance for each setting. Probably use the stock pot on one setting because it's already set correctly for 100% charge (stock setting) and then add a second one for the second switch setting that I would adjust until I reached a 4.1V/cell total output voltage. If it's that close then I assume I wouldn't be stressing the transformer too much.

 

[mlt34]

Why do you want 90% charge rate? In many cases the balancing happens at 100%, so you'll end up with a knackered battery if you don't fully charge it.

Not 90% charge rate, 90% state of charge. Like, up to about 4.1V per cell instead of 4.2V.

Why? Research has shown that charging to 4.1V instead of 4.2 can nearly double the life of the battery. The cost is 10% of your range each time you ride, but if you aren't pushing the limits then it's not an issue. And the adjustable charger means I could charge to 90% most of the time for increased battery health and life expectancy, but also be able to charge to 100% for days that I know I want max range.

EM3EV chargers do the same, but also have a 50% charge setting meant for when you're going to be storing batteries for a long time. They store best at around 50% charge. Stored at 4.2V per cell for long periods is a good way to reduce pack life.

 

[dnmun]

that is not true. research has not shown that. it is just what is assumed from previous life cycle testing.

if you had watched the lecture on the tesla forum by that canadian professor you would understand more about the factors that shorten cycle life.

for all the people here using normal chemistry lipo the best technique is to not charge until the battery is needed. it is time spent at full charge that is critical, not the final charge voltage.

 

[mlt34]

that is not true. research has not shown that. it is just what is assumed from previous life cycle testing.

What do you mean by "it is just what is assumed"? From what I've read, testing has shown that lowering the charging voltage significantly improves the number of cycles a cell can perform before reaching 80% of original capacity. I'll try to find some of this research again to link to. But from what I can tell, this stuff is pretty solidly proven using the scientific method. I know that you know your stuff, and I usually defer to you on issues of batteries and lithium chemistry, but on this one I had thought the research is pretty sound.

[edit: the first link to pop up in google for me was the ES wiki, which has the "90% charge doubles pack life" claim http://endless-sphere.com/w/index.php/Battery_Deterioration ]

Was that lecture you're talking about the one that discussed temperature effects in depth? I've seen a lot of these and they start to run together...

 

[d8veh]

Why do you want 90% charge rate? In many cases the balancing happens at 100%, so you'll end up with a knackered battery if you don't fully charge it.

Not 90% charge rate, 90% state of charge. Like, up to about 4.1V per cell instead of 4.2V.

Why? Research has shown that charging to 4.1V instead of 4.2 can nearly double the life of the battery. The cost is 10% of your range each time you ride, but if you aren't pushing the limits then it's not an issue. And the adjustable charger means I could charge to 90% most of the time for increased battery health and life expectancy, but also be able to charge to 100% for days that I know I want max range.

EM3EV chargers do the same, but also have a 50% charge setting meant for when you're going to be storing batteries for a long time. They store best at around 50% charge. Stored at 4.2V per cell for long periods is a good way to reduce pack life.

You won't make your battery last any longer. It'll go out of balance and your range will go right down until you have to open it up to sort it out. The idea of not charging to a li-ion battery to 4.2v per cell is ridiculous. It would be different if there were no BMS, like with lipos.

 

[amberwolf]

As far as balance of a pack that isn't "fully charged" each time goes, that depends on the cell quality (and possibly chemistry), age, and the BMS's HVC/balance points (if it has a BMS).

My EIG NMC pack doesn't appear to (yet) have any balance issues, regardless of the SoC I check it at; though I haven't run a full-discharge test in a while. Haven't checked the cell-man A123 pack.

From what I've read, testing has shown that lowering the charging voltage significantly improves the number of cycles a cell can perform before reaching 80% of original capacity.

Well, it would have a similar effect to not charging except when needed, because it spends more time at a lower voltage.

Though, in this case it spends more time "mostly" charged, whereas what dnmun is talking about would spend more time with less charge than that, and presumably even longer cycle life.


The problem with the second method is that it's not always practical to charge only when needed, as the time of need may not be fully predictable.

In my case, I have my work schedule that gives me general predictability of when I will need at least a few Ah for the commute. So I don't in theory have to keep the pack fully charged all the time--but:

There are also times when I find out while I"m already out there I need to go a lot farther than I'd planned, and haven't time to go home and charge first. So I generally need to keep the pack on the bike fully charged for the extra range capability even though most of the time I don't need it.

But there are others that don't need the bike at any particular time, and just feel like using it sometimes, or those that never need extra range like me, but are on a predictable schedule and route, and they could probably benefit greatly from not charging it until they need it.


Another But: someone that has a small pack that tends to go out of balance when fully used, who also uses most of their capacity on a predictable run, will need to charge for a much longer time so their pack will balance, and will need to start the charging process much earlier, meanign more time at full charge. If they have to use it every dya and it takes overnight to balance, then in practice they pretty much have to keep it fully charged all the time.


So there are scenarios where not charging until it's used will work, and help extend life, and other scenarios where it's probable that the only practical way to extend life is just to not quite fully charge (lower HVC).

 

[d8veh]

The BMS has a balancing system for a reason: It's needed to balance the battery. Most (not all) BMSs use bleed resistors to do the balancing, which don't open until the cell voltages are near maximum. If you charge to 80%, they will never open, so no balancing. If you want to take a chance, good luck.

 

[mlt34]

Isn't the ability to charge li-ion ebike batteries to less than 100% one of the main point's of Grin Technology's new Cycle Satiator charger? If this would ruin packs, shouldn't someone have said something to them before they wasted three years and tens of thousands of dollars developing their charger?



I'm not disagreeing with you guys about the purpose of BMS's and how they work. You're correct that packs need BMS's and that they balance cells. But that's missing the point. If the goal is to be able to generally keep the pack nearly full but not to the point of a large reduction in cell life, then this can be done by often charging to 90% instead of 100%. The cells should more or less stay balanced after a few rides even when only charging to 90%. The goal isn't to never charge to 100%. That's why I want it to be adjustable with a switch or pot, as stated in the title and description. That way it is user selectable: 90% for days I want to be more conservative, 100% for days I want normal, full charging. Anytime I charge to 100%, the cells will of course balance. I agree that modding the charger to be a permanent 90% SOC charger would not be advisable, but that's not what the goal is.

If this didn't work, then ebikes.ca and EM3EV would be having serious business problems by now...

 

[dnmun]

i cannot make you listen to the lecture but don't assume what people post up here or on battery university in any way compares to the research that the professor in that lecture presented. i think the fact that elon hired his grad student to head up his battery lab says a lot.

mitch has pulled up a link:

http://evobsession.com/li-ion-batteries-die/

another about the parasitic reactions:

http://gizmodo.com/scientists-solved-the-mystery-of-why-rechargeable-batte-1583247838

solid solution zone of lifepo4:

http://www.renewableenergyworld.com/rea/news/article/2014/06/seeing-how-lithium-ion-battery-storage-works

 

[mlt34]

Yea, I definitely want to finish it. I started it a week or two ago but didn't have time to watch the whole thing. I was still in the temperature effect region in the beginning. I need to watch the rest of it though, you're absolutely right. I don't claim to be a battery expert by any means, and so I want to learn from the experts.

 

[DrkAngel]

See - MeanWell S-150-48 Mega-Mod
V-A meter required <30V secondary power ... which I was able to pull from a diode. (Test from common neg to pos ends of diodes to find compatible voltage point)
0-100V 10A meter <$5 Below picture - Make sure the meter you buy has pots to correct-adjust voltage and amperage. Also, adjust V at 0A drain, because V seems to shift slightly under load, you want the final "full" voltage to be accurate.

 

[justin_le]

The BMS has a balancing system for a reason: It's needed to balance the battery. Most (not all) BMSs use bleed resistors to do the balancing, which don't open until the cell voltages are near maximum. If you charge to 80%, they will never open, so no balancing. If you want to take a chance, good luck.

You raise a good point that can come up in some circumstances but it's less of an issue than you make it seem.

Cheap BMS circuits usually have a behavior you describe where there cells will only bleed when they are above some threshold like 4.15 or 4.2V. Almost all the programmable BMS IC's let you determine the bleed conditions based on a given spread in voltage between the cells, and/or being above a certain voltage and charging/discharging state. So some will bleed the high cells whenever the spread between high to low is greater than 0.05V regardless of the voltage but only if the pack is charging, not when it is discharging. OR, it might bleed balance when the cell spread is >0.05V but only when the cells themeslves are over 4V. There are many implementations and they don't usually follow the simple dumb logic of "bleed cell if Vcell > 4.XXV".

The other thing is that packs made with good quality cells rarely need much balancing action at all. You can do 50 or 100 cycles on a string of panasonic, sony, LG cells etc. without any active cell balancing and their voltages will still match almost identically. It's really just the rubbish cells that require such constant maintenance.

So as to the topic at hand, of routinely charging to less than a 100% charge for reduced exposure to high cell voltages and better cycle life:

Good cells + Good BMS = no problem
Good cells + Basic BMS = no problem
Crappy cells + Good BMS = no problem
Crappy cells + Basic BMS = problems

But even in the case of crappy cells with a basic BMS, so long as every 10 or 20 cycles you run the pack to full voltage to enable a top-up balancing, then there is no real downside.

 

[mlt34]

The BMS has a balancing system for a reason: It's needed to balance the battery. Most (not all) BMSs use bleed resistors to do the balancing, which don't open until the cell voltages are near maximum. If you charge to 80%, they will never open, so no balancing. If you want to take a chance, good luck.

You raise a good point that can come up in some circumstances but it's less of an issue than you make it seem.

Cheap BMS circuits usually have a behavior you describe where there cells will only bleed when they are above some threshold like 4.15 or 4.2V. Almost all the programmable BMS IC's let you determine the bleed conditions based on a given spread in voltage between the cells, and/or being above a certain voltage and charging/discharging state. So some will bleed the high cells whenever the spread between high to low is greater than 0.05V regardless of the voltage but only if the pack is charging, not when it is discharging. OR, it might bleed balance when the cell spread is >0.05V but only when the cells themeslves are over 4V. There are many implementations and they don't usually follow the simple dumb logic of "bleed cell if Vcell > 4.XXV".

The other thing is that packs made with good quality cells rarely need much balancing action at all. You can do 50 or 100 cycles on a string of panasonic, sony, LG cells etc. without any active cell balancing and their voltages will still match almost identically. It's really just the rubbish cells that require such constant maintenance.

So as to the topic at hand, of routinely charging to less than a 100% charge for reduced exposure to high cell voltages and better cycle life:

Good cells + Good BMS = no problem
Good cells + Basic BMS = no problem
Crappy cells + Good BMS = no problem
Crappy cells + Basic BMS = problems

But even in the case of crappy cells with a basic BMS, so long as every 10 or 20 cycles you run the pack to full voltage to enable a top-up balancing, then there is no real downside.

I'm sold. Literally. Here's my CS :lol: :lol: :lol:


It's so pretty

 

[hagerty1]

Ok maybe I'm in the right place maybe not.... Sorry if Not
I have a batch of 10 chargers for 13S Lithium Ion packs along with 13S BMS
I was sure I would run 13S when I ordered them. i have now discovered I wish to
run 14S. The charger is Automatic CC CV and set to 54.6V 3.5A. There is a pot inside
that seems to control voltage. My question to you all is how do I test the output voltage
of the charger ? With no battery connected it puts out nothing. With a 13S pack it puts out
whatever the pack voltage is and rises with the charge cycle then drops amps to about .5 amps
at 54.6V until pack is saturated then shuts down. I am charging through a balancing BMS.
I hooked it up to a 14S pack and it flashed cycled on off trying to get it's voltage up like my Meanwells
do when I overload them.I (MY BAD) turned the pot to see if I could get the voltage up but the hunting
would not stop. I was running the input through a meter (60V max unfortunately)
When I disconnected the pack an still had the charger on it was putting out 71V (POOF went my meter)
I also discovered that it had hit the BMS with over voltage and the auto HV shut it down.
I guess what I'm asking is how do I adjust the pot correctly without connecting it to a battery pack, or
is it even possible? I know they can easily put out the 59V I need if I can get them adjusted. Can I connect it to a static 3.5 amp load? I assume it needs voltage feedback??? It would save me a bunch of money if I don't have to buy all new chargers. I already have to buy new 14S BMS units. Any Help ?????
I think pictures http://s161.photobucket.com/user/hagerty11/library/?sort=3&page=1

 

[DrkAngel]

I guess what I'm asking is how do I adjust the pot correctly without connecting it to a battery pack, or
is it even possible? I know they can easily put out the 59V I need if I can get them adjusted.

Discharge a 14s pack to <54.6V (≤3.90V per cell).
Attach charger through V-A meter.
Test adjustments in small steps ...

 

[dnmun]

measure the output voltage in front of the relay. you did not post up a picture here, just in the hosted site. post up some VGA pictures of the backside. here.

 

[DrkAngel]

I guess what I'm asking is how do I adjust the pot correctly without connecting it to a battery pack, or
is it even possible? I know they can easily put out the 59V I need if I can get them adjusted.

Discharge a 14s pack to <54.6V (≤3.90V per cell).
Attach charger through V-A meter.
Test adjustments in small steps ...

Using thin gauge charging leads (jumper wires?) will allow noticeable voltage differential between charger and battery - while charging.