PL 8 - Q and A section - How to Set up - Use etc,

[snaker]

Glad your low cell survived, snaker.

Out of curiosity, how many Ah was returned?

I charged it in 2 stages. Firstly, I charged it from 2.7V to 3.2V at 2A => 3Ah returned. Then I charged it full at 12.5A => 73.5Ah returned. So total Ah is 76.5Ah.

[shirley_hkg]

After a night, their voltage drops and stays at 3.4xx as expected.

It seems they are of VERY good quality .

[Gnomatic]

Glad your low cell survived, snaker.

Out of curiosity, how many Ah was returned?

I charged it in 2 stages. Firstly, I charged it from 2.7V to 3.2V at 2A => 3Ah returned. Then I charged it full at 12.5A => 73.5Ah returned. So total Ah is 76.5Ah.

Thanks. So that REALLY discharged cell is still full capacity. Excellent!

[Burgerman]

Not nesassarily. What you replace isnt the cell capacity. A high resistance cell will waste energy as it is charged so more goes back.

Te actual capacity is measured on discharge testing. The difference is the efficiency.

[snaker]

I finished full charging all cells and step into the discharge stage. As I remember, when I clicked on Start button I saw the "n CYCLE" option. Now the "n CYCLE" option disappears as the image below. Does it depend on presets? How to get it back?

PL8.png (10.5 KiB) Viewed 11294 times

[Burgerman]

You dont really want it back. Actually I only ever used it on metal hydride.

But:

[c500user]

I plan to buy a PL8 but just saw that the dual version is on special and only $30 dearer.
http://www.store.revolectrix.com/Produc ... l-PowerLab

Any reason not to buy the dual version?

[shirley_hkg]

Check out page 15 of this thread .

[c500user]

Check out page 15 of this thread .

Thanks, I missed that. Shame it is not identical as 2 PL8's.

[Burgerman]

One big issue is that I cannot send you a properly configured preset with extended and corrected parameters. So it will give a few errors periodically.

[snaker]

I discharged some of my 17 cells. Their capacity out is all around 70Ah. They seem Ok.

The total cost of these 17 cells is even cheaper then 150Ah@24V generic lead acid batteries (not talking about gel or high quality ones yet). A friend wants to buy these cells to build his solar system (about 1kw/h). He also wants a good charger like PL8. Can PL8 be used for a solar system?

[Burgerman]

No. Thats where things can get complicated. My solarsystem is complicated... Most are. The solar power in my case uses 3 different solar power (100V, 30V, 30V nominal devices with solar tracking that holds the panels atthe best voltage to get max efficiency/watts. Thats different depending on solar radiation, panel spec, temperature etc and varias throughout the day over 10 volts or so.)

These convert to mains voltage and frequency, and track the house AC waveform so that they can inject power into the house at the correct frequency and mains voltage etc. IF they add enough power so that they generate more than I use, the power is diverted to charge a stack of old powerchair batteries @ 48V. The charge voltage and rate of charge etc depends on a lot of things. At night or if cloudy, once the house is using more power than I generate, the extra comes from the battery. If I take more current or more charge Ah than this can provide it comes from the street or both. This is all programmable...

So its not just a charger... Although you could just manually use a power supply powered by the house when the sun is shining with a grid tie inverter, to charge with the PL8 periodically. But you would be monitoring, deciding what to do and when, all the time.

Also 1kwh wont do much good. It will run my PC for a couple of hours. Or boil a full kettle twice. Or almost charge a wheelchair.
You need 10x that to be useful. My solar system generates about 10kwh per day. (5 in winter. 20 in summer). Dep on weather. And its seldome smooth! You get about 30V at 9 to 10A per panel, and theres 10 of those. So your battery in that case and charger would need to charge at 100A when the clouds move... Or the power is wasted. Often much of the day.

In this case, a BMS and a simple CV regulated charger set to say 3.5V per cell is the only simple way to do as he needs. But say a small single 100w solar panel can generate a 1 kwh in summer if no cloud. But most days will be half that. And in winter it will be under 1/4 of that. So you need to use a lot more panels. And then you need to be able to take advantage of the large currents generated at the times when it does!

[Gnomatic]

This is quite interesting.

How could this work best with an RV or camper, and what would be needed, for someone looking to top off the camper battery(assuming LiFePO4) with portable solar cells when not charging from the grid?

[Burgerman]

You would just use MPPT charge controller, as I use on my van. And a solar panel. Set charge controller to 3.5 or 3.55 volts x 8. (or x4 for 12v). So 14 or 28 volts.

http://www.ebay.co.uk/itm/LCD-10-20-30A ... WWWUeABBcw

Most of these are crap. This one works well.

And a BMS... And hope for the best.

[Gnomatic]

You would just use MPPT charge controller, as I use on my van. And a solar panel. Set charge controller to 3.5 or 3.55 volts x 8. (or x4 for 12v). So 14 or 28 volts.

http://www.ebay.co.uk/itm/LCD-10-20-30A ... WWWUeABBcw

Most of these are crap. This one works well.

And a BMS... And hope for the best.

Just looking around, this BMS seems rather programmable. Looks pretty cool.

http://electrodacus.com/


youtu.be/bg1x6X8tZok

[Burgerman]

Its a nicely packaged bms... But it can charge from a 100A solar array, but with 5x less balancing current that a hobby charger. And when it says 200mA max, that means you only get the "full" microsopic 200mA when a cell is a lot over the set point. (PL8 for eg does a 1000mA and throttles the charge and some hobby chargers can balance at 3000mA. And you only see the "full 200mA" if they are miles out (actually less as shown). And without a closer look it likely does the same as all these things do, and chops off charger power and isnt proportional. So likely will repeatedly overvolt cells then pull them all down again, as it tries to charge/balance the high ones. The issue stems from the fact that he uses a common BMS chip to build his thing around. So it looks pretty. Still inadequate, and probably in the wrong place. Depends if it can do the same as a hobby charger while simultaniously having accurate MPPT built in to track max power voltage of the panels during the day. And if it has adequate programmable parameters.

On his demo, it shows a 62mV differnce (thats huge on a LIFE cell at say 70% charged. And it shouldnt even be trying to balance there anyway. And it shows only a few mA balance current. Ask yourself. Why? The PL8 for eg will drain 1000mA if it sees a 4 or 5mV difference! And it will only do so above 3.5V on a LiFePO4 cell. As I programmed. To do it earlier UNBALANCES the pack. So fancy looking, all wrong... Likewise when he discharges one tiny AA sized cell, it took more than a full charge cycle to rebalance, and it does so by disconnecting the charge when the others are full... Its probably OK for solar, long term, if all cells are healthy, and in balance. But hopeless on an EV. Its a BMS in a pretty case with a lot of user settings. But its working method is fundamentally flawed. Unless it works like a hobby charger. But thats not what we are seeng here.

So without disecting and testing I cant say it WONT be OK but really, all you need is a cheap charge controller and solar MPPT thing that I linked to. And a 5 dollar BMS will work just the same as far as I can tell.

[Burgerman]

E.G...

https://youtu.be/bg1x6X8tZok?t=1502 at this point he shows whats wrong with the typical BMS... It may be programable and have a fancy display but it goes about its job in the wrong way. Whats more it shouldnt be balancing below 3.5v or it will put the pack OUT of balance! And it shouldnt take any more than one cycle to charge and fully balance to 1mV accuracy. On a huge battery. He is using 8 tiny cells or supercaps.

So as soon as the highest charged cell reaches some point that is above charge voltage it turns off charge while it sucks out some power... Repeatedly.

Since he is charging tiny cells it looks OK here. Because the 200mA is a large proportion of the charge current. But charge at 40A and see what happens! On a pack thats 150Ah and out of balance! His was still miles out after 3 cycles. You might get away with that on solar after a week or two it will be balanced! If it were to only balance at the top.

Heres its problem. It doesent balance at the TOP. Or the BOTTOM. It balances all the rest of the time. Theres 2 things wrong with that.
1. If you have a large pack that is say 1Ah out of balance, and you use this to charge it it will only end up balanced after many many cycles. Since it STOPS BALANCING once the cells are charged. Or rather when the highest cell reaches the preset point. Thats it! No CV stage. No balance at CV.

2. On a big LiFePO4 pack, you can only balance at the top. Or at the bottom. You CANNOT and should not try to balance in the normal usable range. Why? Because the cell with the highest temperature, or with the least impurities, or the highest resistance will show as higher or ower voltage even when the pack is in perfect balance. So trying to accurately level the voltages actually UNBALANCES the pack all day long! Not only that discharging a cell warms it up. Which increases voltage... Rinse and reapeat. So on subsequent charge the thing is miles out of wack. So the guy may be a keen electronics guy but hasnt a clue about batteries.

For those that dont believe it, set your PL8 from 3.5V balance start, to a low figure. And then charge slowly. See what a mess it makes of the charging and rebalancing at the top!

[Gnomatic]

E.G...

https://youtu.be/bg1x6X8tZok?t=1502 at this point he shows whats wrong with the typical BMS... It may be programable and have a fancy display but it goes about its job in the wrong way. Whats more it shouldnt be balancing below 3.5v or it will put the pack OUT of balance! And it shouldnt take any more than one cycle to charge and fully balance to 1mV accuracy. On a huge battery. He is using 8 tiny cells or supercaps.

So as soon as the highest charged cell reaches some point that is above charge voltage it turns off charge while it sucks out some power... Repeatedly.

Since he is charging tiny cells it looks OK here. Because the 200mA is a large proportion of the charge current. But charge at 40A and see what happens! On a pack thats 150Ah and out of balance! His was still miles out after 3 cycles. You might get away with that on solar after a week or two it will be balanced! If it were to only balance at the top.

Heres its problem. It doesent balance at the TOP. Or the BOTTOM. It balances all the rest of the time. Theres 2 things wrong with that.
1. If you have a large pack that is say 1Ah out of balance, and you use this to charge it it will only end up balanced after many many cycles. Since it STOPS BALANCING once the cells are charged. Or rather when the highest cell reaches the preset point. Thats it! No CV stage. No balance at CV.

2. On a big LiFePO4 pack, you can only balance at the top. Or at the bottom. You CANNOT and should not try to balance in the normal usable range. Why? Because the cell with the highest temperature, or with the least impurities, or the highest resistance will show as higher or ower voltage even when the pack is in perfect balance. So trying to accurately level the voltages actually UNBALANCES the pack all day long! Not only that discharging a cell warms it up. Which increases voltage... Rinse and reapeat. So on subsequent charge the thing is miles out of wack. So the guy may be a keen electronics guy but hasnt a clue about batteries.

For those that dont believe it, set your PL8 from 3.5V balance start, to a low figure. And then charge slowly. See what a mess it makes of the charging and rebalancing at the top!

I guess that begs the question (at least from me), why doesn't someone make a BMS that behaves the 'right' way, the way the PL8 behaves using presets several of us here use on our chair packs?

[Burgerman]

Quick answer. Charging is only ONE thing a BMS does. And its in the wrong place to do it. Hence the problems. So you either need a PL8 on board as part of your BMS as a full size car manufacturer would do. (Embedded charger is IN the car you just add power.) Adding 200 dollars to every battery. Or you do it with a cheap 5 dollar BMS.

Well thats a SOLAR bms not a normal BMS. So if it tries to balance a battery pack at the top as the PL8 does, then it would be needing to control both the solar current (that varies due to clouds, and MPPT algo cycling etc, and try toalso control charge current at the same time with a varying input level. And remain below its feeble 200mA balance /charge level. Which isnt really practical. So instead it just stops charging when the highest cell hits say 3.6V... And tries to balance in use, and at varying voltage. Which sort of works in a fasion on most lithium types but will certainly cause srious unbalance not LiFePO4... So we will ignore that BMS as its a different case.

The reason they dont NORMALLY do it right is because the BMS job is to allow you to fit "a battery" into an unsuitable situation. So your dumb ebike enthusiast, buys a batery. He wants simple. So it always has a BMS. And a 5 dollar BMS protect the battery from him, in a fashion. Or it would need to be replaced by an ON BOARD PL8 complete with its phone book worth of complex computer code, and its expensive components.

The BMS is choosen to protect the BATTERY from
1. OVER CURRENT. You accelerate your e-bike, and it chops off power. The seller or the battery has no idea what the max Amps the ebike or whatever it is fitted to will pull. So it allows up to the cells maximum safe level. So then if the battery is big enough for the job, or high enough C rating for this current, then the BMS will never trip or do anything atall as it doesen NEED to protect anything! In other words if the BMS does trip, then you need a bigger battery or a better current controlled power modue... But this trip figure depends on motor impedance, battery size, the Amp level that the controller allows (and typical ebike ones are simple and unlike ours do not have any in built current or voltage limits). So its all unknown. So BMS saves battery from fool/incorrect choices.

2. Same applies to charge current.
3. Same applies to charge Volts.
4. Same applies to EVERY stupid thing that the BMS doesent need to do, and theres about 10 of them. Provided the battery C rate, and capacity is matched to and exceeds a known maximum load / or current limiting controller. And if the chargers voltage is correct, and if the charger amps dont exceed max current limit then the BMS simply wont trip and isnt required. We dont need any of this garbage. Because we choose the cells, capacity carefully and charge correctly with the proper current/voltage.

What other things does the BMS do that are useful?
1. It watches the battery LOWER voltage, and the CELL voltage in use. If you run it too low. If we exceed that safe point it pulls the plug and we stop. Again this isnt a safe scenario in a powerchair. OK in a laptop or drill. You may be crossing a busy junction. Worse, because its on/off only and not proportional so you never know when. It watches volts. Which instantly drop under heavy loads as you try to leave a road, enter a train. So it may well cut out while on a ramp trying to enter a train. Any time of heavy demand. What we need is a MONITOR so we can decide when its safe to stop and charge. These are cheap. Or better still fit enough battery so its never a problem! My approach. Which has many other benefits too. In any case many chair controllers can also monitor voltage and REDUCE POWER proportionally in a safe controlled way under load, to maintain battery voltage to a minimum level you choose. And the built in battery meters can be calibrated to suit lithium in many cases. At least on some controllers such as on the Dynamic ones and I think R-net. So we dont want that "function" either!

2. Charging. It balances cells. And cuts off charger oif Amps or Volts are exceeded. Meaning a 2 wire dumb charger can be used. Many people like this. Its simple. They lack balance power. And balance accuracy. And often try to balance the full charge rather than just at the top. Or all the time in use! Or are set to 3.65V meaning they allow 3.7V peaks or sometimes much more. And they take an age to balance due to 50 to 100mA current levels. While repeatedly cutting off the chargers power via an on/off mosfet. Theres no other way they CAN do this with a 2 wire charger. Make and break... If you take all the balance wires out to the charger, as I do, you may as well just use a far more accurate and tunable PL8!

So they offer a crappy way to balance cells and charge, and we dont want or need anything else they "offer" if properly implemented. Since NONE of those things will ever trip as we are already taking care of these things in a far better way.

[steves1977uk]

One big issue is that I cannot send you a properly configured preset with extended and corrected parameters. So it will give a few errors periodically.

Can be done now BM!

Steve

[Gnomatic]

Thanks for the thorough reply.

BMS seems temping because of simplicity. But really I've had little issue using your presets with the PL8, even while traveling. My PSU went belly up while I on the road, and I really wished I had my van wired up similar to the way you do so I could charge during long drives. I'll have that done before I hit the road again. I had another PSU sent to where I was going, but it'd be nice to be able to charge in the van if needed.

[Burgerman]

Can be done now BM!

Steve

Nope... 350mV cell voltage difference before safety charge 500mA garbage cannot be used due to firmware difference amongst other things. Which happens on an out of balance large lifepo4 pack. Check the preset you use. Then try setting that on a DPL8... And you will see. Its firmware is more safety nazi'd.

[Gnomatic]

So I got a new PL8. Both times I've charged with it, the charger gets well into the CV stage, but stops when the current falls to 1.5A-2A, On the charger itself, it says "PACK REMOVED (Undercurrent)." It won't complete the charge.

Any clue what's happening?

[Burgerman]

Never saw the undercurrent. But pack removed I have. Bad connection to pack usually. Or unstable power supply/bad connection there? If not theress maybe a fault. So check, and if it doesent go away, return it as defective.

I sometimes see that when I rapidly swap my camera batteries over quickly while its still cv charging. If you do it fast enough it just carries on.

[Burgerman]

I see two reasons why this may have happened.

Your power supply has a full volt and a bit change between on load and off. (this is pulse width controlled). Thats not great. But alone will cause no problem. Mine varies by 1/10th of a volt.

In addition its not well regulated as evidenced by the wavy line showing that current on charger input and cell being charged varies up and down most of the time along with the volts. It makes the charger hunt all the time as it tries to adjust to the varying supply. This means it may see the voltage drop below the termination current you have set before it should. Hence charger sees an error or thinks the pack has vanished?

But this is made worse due to the battery CV voltage coinciding with the swap from buck to boost. Theres 2 seperate inverters in the chargers. One can charge a battery lower than input voltage. One charges a battery at higher than input voltage. Because your charger sees a voltage rise, from the power supply, as it reduces current, it then tries to swap to buck mode. As it does so and adds current, the voltage from the power supply falls again... So it keeps swapping...

Solution, a more stable supply. or set the power supply voltage well above or well below the CV voltage. A couple of volts below CV is the worst possible option.

You can change CV slightly, better still change power supply volts. Or try setting a higher frequency for conversion.

Heres how I know!

[Gnomatic]

I ordered a refurb unit from Revolectrix to have a backup charger on hand. Should get here today. Next time I charge, I'll use the refurb unit and see if the error is still there. If not, I'll return the new PL8.

[Gnomatic]

My PSU is a pair of 12v server PSU's cobbled together and wired in series. The only way I can change the voltage on it is not plug in one of it's server PSU's. In which case the overall PSU runs @12v.

[Burgerman]

Well here is an example of my bench supply, both are equally good.

This is the voltage while charging my lipo batteries in the bot... these are charging at 3A and its currently falling down to around 1A.
Thers just 0.18V difference loaded and unloaded. And the loaded volts are ABOVE the unloaded.

[Burgerman]

Set CV voltage to a higher or lower voltage, and set frequency to higher or lower speed. It will likely not do it then. First be sure no bad connection.

[Gnomatic]

Well here is an example of my bench supply, both are equally good.

Looks much tighter than mine, no doubt. I'm guessing those weren't cheap!