Possible to bulk charge in parallel with individual chargrs?

I've got a 3kW, 24V, mean well power supply and like to fast charge large format A123 on the fly, was wondering if it was possible and safe to parallel the RSP 3000/24 with 8 individual 3.65V, chargers daisy chained (series across the bulk charger)

Please tell me if I'm crazzzzýyyy.

I'm not quite sure what you're intending, but IIUC, you're meaning that you already use the little chargers on each series cell? And you then want to put the MW across the whole pack at the same time?

If so, well, I'd guess that it depends on how those chargers react, and whether hte MW's voltage is higher or lower than the actual voltage of the total series chargers. If' it's lower, then I don't imagine it will do anything at all. If it's higher, then having the other chargers doesn't do you any good, cuz they won't do anything and the MW will simply charge up the pack to it's higher voltage.


Now, if the MW is lower voltage than the total series chargers, but you don't connect those little chargers while using the MW, then you could use the MW to do bulk charge of hte pack first, and then connect the little ones to bring them up the rest of the way.


It might work differently than the above, but that's how it seems to me with my sleep-deprived brain ATM.

Yes it's a combination of bulk, taper charge and balancing.
I was thinking with Lifepo4, because the 'knee' to fully charged is so fine and the miniscule difference in IR, the cells have a tendency to drift apart without balances early on.

I like to fast charge A123, 20 large format in about 2C on road.
So was thinking of small individual chargers or a balance charger across the cells and heavy current bulk charger parallel across it.
Say bulk RSP 3000 is set to around 8x3.5V on start up, current rises heavy around 3C, small balance chargers are switched on and RSP voltage is ramped up over say 10-15 min to around 8x3.65V.
Would the effect of having them seriesed and paralleled affect the operation of each other, or would it be mutually benifitial,
E. g no smoke, noise & light show?

Hope you managed to get some sleep, yawn I was up at 3 am too yawn, know the feeling.

If the MW's voltage is not quite as high as the total series of the small chargers, then I guess with a diode in the output of the MW (which might already be present or might have to be added) ot prevent any feedback from the series chargers, or a fully charged pack, then they ought to all be ok together. If the MW voltage is as high or higher than the small chargers total, then it could b epossible for the MW to either overcharge the pack or to backdrive/etc one or more of the chargers.


YOu can sort of think of it as having a bunch of batteries in parallel and series. Everything tries to be a the same voltage...but in the process, currents have to flow thru the things that are lower in voltage than others in parallel with them, and whatever ahs the lowest internal resistance has the highest currents.

If there are diodes to prevent current flow back into lower voltage outputs, then there's no worry about that, but in the case of the little chargers their output is so low voltage you don't want to put diodes on them if they aren't already there. The MW could be adjusted to compensate for the diode's voltage drop (which will change as current flow changes, but probably you only need to worry about it's highest current level, really).

amberwolf said:

If the MW voltage is as high or higher than the small chargers total, then it could b epossible for the MW to either overcharge the pack or to backdrive/etc one or more of the chargers.

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Yes that was my worry

amberwolf said:

YOu can sort of think of it as having a bunch of batteries in parallel and series. Everything tries to be a the same voltage...but in the process, currents have to flow thru the things that are lower in voltage than others in parallel with them, and whatever ahs the lowest internal resistance has the highest currents.

Click to expand...

You explained that brilliantly

amberwolf said:

If there are diodes to prevent current flow back into lower voltage outputs, then there's no worry about that, but in the case of the little chargers their output is so low voltage you don't want to put diodes on them if they aren't already there.

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Will 4V chargers+ series schottky diode have approx 0.4V forward vd, do the job?

Problem with diodes is their voltage drop varies iwth current, so it could greatly affect the little chargers' ability to do the balancing you want them to do.

Wouldn't make that much difference to the bulk charger part....

I'm not exactly sure if I'm already doing what your asking about. My lifepo4 packs are all 24v - 20ah without BMS. They all have Anderson connectors for both bulk charging (or discharging) and individual balance charging (12 connectors in all per pack - 1 is a dummy though). I prefer to use the individual chargers each time. But when I'm in a rush I will connect both a bulk smart charger at 6a and the 8 individual chargers at 2a each. When my CellLog8 alarm goes off on high voltage for an individual cell I unplug the bulk charger and let the individual charges top off the low cells.

Honestly, it's not the greatest system in the world but it works. Remember that your cells are still in series so your individual chargers need to be self isolating. I am considering getting individual high amp bleeders and connect them to the individual charger connections instead of fooling with the individual chargers. It would be pretty much like how a BMS works for charging except a much higher bleed rate capability.

Bob

dumbass said:

I'm not exactly sure if I'm already doing what your asking about. My lifepo4 packs are all 24v - 20ah without BMS. They all have Anderson connectors for both bulk charging (or discharging) and individual balance charging (12 connectors in all per pack - 1 is a dummy though). I prefer to use the individual chargers each time. But when I'm in a rush I will connect both a bulk smart charger at 6a and the 8 individual chargers at 2a each. When my CellLog8 alarm goes off on high voltage for an individual cell I unplug the bulk charger and let the individual charges top off the low cells.

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Thanks mate, that's what I'm talkin bout.
I really haven't got that much trust in BMS' s and I feel most of them are just too complicated, expensive, slow, lossy and not foolproof.
Can I ask what individual chargers are you using?
The cellog alarm output could be used to switch the bulk off and return to individual and maybe cycle that option??? hmmm.
Hopefully pumping @3 or 4C won't back feed the individual chargers, I wonder if yours already have something on the output?
What do you think Amber?

dumbass said:

Honestly, it's not the greatest system in the world but it works. Remember that your cells are still in series so your individual chargers need to be self isolating. I am considering getting individual high amp bleeders and connect them to the individual charger connections instead of fooling with the individual chargers. It would be pretty much like how a BMS works for charging except a much higher bleed rate capability.
Bob

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Having a 1 ohm 5Wter, fix one end on output and have the other end connected to a springy copper intermittent switch.
Are your chargers slightly overvolting, are they not at 3.65V mark, or are you seeing floating overvolting, caused by the upset by the paralleled bulk charger, so your having to bleed?
Could be as amber mentioned and as you said becomes not the best set up, when the setup is trying to overvolt certain cells??

amberwolf said:

Problem with diodes is their voltage drop varies iwth current, so it could greatly affect the little chargers' ability to do the balancing you want them to do.

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I'll have to look into that, was hoping to use 4V with a schottky for a lower vd.

Then we are talking the same thing for the same reasons. The individual chargers I am using have no manufacture name on them. But they have a model #hxy-036v2000a. They are actually 3.6v @2a. I find that they charge in the 3.62v range. I bought them from http://www.voltphreaks.com/ a few years ago. I look at their site just now and can't find these little chargers. So they may not be handling them anymore. Hard to believe that though because they were selling tons of them at about $10 each.

My CellLog8s are built into the packs with 100db alarms activate by their alarm outputs. But I agree you could use the output to trip a relay to turn off the bulk charger. My original intension was to build the individual chargers in a small plastic case and install their own CellLog8. Then wire in a relay to trip the bulk charger at 3.65v. Just never got it done.

Bob

dumbass said:

http://www.voltphreaks.com/ a few years ago.

Then wire in a relay to trip the bulk charger at 3.65v.
Bob

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Thanks mate.
I've come across volt freaks on the site before, many moons ago, at that price I'll have to look them up, that's good for me.
Rather than use a relay, it may be simpler for me to enable/disable a pin on the RSP3000 control pins, which then could be done straight of the cellog alarm output port.
Have you have similar control pins with your charger?

megacycle said:

dumbass said:

http://www.voltphreaks.com/ a few years ago.

Then wire in a relay to trip the bulk charger at 3.65v.
Bob

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Thanks mate.
I've come across volt freaks on the site before, many moons ago, at that price I'll have to look them up, that's good for me.
Rather than use a relay, it may be simpler for me to enable/disable a pin on the RSP3000 control pins, which then could be done straight of the cellog alarm output port.
Have you have similar control pins with your charger?

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LOL, sorry but your talking a bit over my head electronically. One thing I will warn you about is to watch the current load on the CellLog8 output circuit. It's very limited (90ma if I remember correctly). But some folks here have replaced components in the units to handle higher currents.

Bob

dumbass said:

LOL, sorry ,but your talking a bit over my head electronically. One thing I will warn you about is to watch the current load on the CellLog8 output circuit. It's very limited (90ma if I remember correctly). But some folks here have replaced components in the units to handle higher currents. Bob

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I'm lead to believe the spec is 500mA.
But the 0.5A limit is no matter anyways, either relay or connect alarm output, to charger control pin, generally speaking, a voltage controlled pin, on my RSP3000, if this is grounded, it shuts down.
So if a large value resistor goes from (+) on the battery to alarm out, and alarm out is able to control the RSP3000, this way.
I was wondering, if your charger had control pin, to shut down similarly?

megacycle said:

dumbass said:

LOL, sorry ,but your talking a bit over my head electronically. One thing I will warn you about is to watch the current load on the CellLog8 output circuit. It's very limited (90ma if I remember correctly). But some folks here have replaced components in the units to handle higher currents. Bob

Click to expand...

I'm lead to believe the spec is 500mA.
But the 0.5A limit is no matter anyways, either relay or connect alarm output, to charger control pin, generally speaking, a voltage controlled pin, on my RSP3000, if this is grounded, it shuts down.
So if a large value resistor goes from (+) on the battery to alarm out, and alarm out is able to control the RSP3000, this way.
I was wondering, if your charger had control pin, to shut down similarly?

Click to expand...

You maybe right about the 500ma. It's been a while since I read the specs. I just don't remember it being that high.

Sorry but your pin question is still over my head. If there is this capability I don't know if it. Sorry I can't give you better info.

dumbass said:

You maybe right about the 500ma. It's been a while since I read the specs. I just don't remember it being that high.

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http://www.jun-si.com/EnProductShow.asp?ID=96
50V, 500mA.

dumbass said:

Sorry but your pin question is still over my head. If there is this capability I don't know if it. Sorry I can't give you better info.

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Yes your charger probably has the power out connections only.
It would have to be relay controlled, no problem at the 6A ratings, bigger relays at 60A.
Thanks Bob.

No problem and good luck with your setup.

Bob

dumbass said:

No problem and good luck with your setup.
Bob

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Cheers Bob thanks for the help.
I think I'm going to get some 24V- 3.6Vish, DC-DC converters, instead of AC-DC, as you say the voltfreaks have gone and 24V- 5V@30A is available in small package, if I want to go either single charger only as well.
Cheers Jeff

Jeff,

Take a look at theses. I was quoted $2.60 each from the supplier. Note they are cell bleeders and not chargers. I was told they can be used in parallel while the pack is wired in series. I am looking at these because I am having problems with the single cell chargers actually balancing the cells properly. I find that while charging 8 cells (each with it's own 3,6v 2a single cell charger) the cell voltage is all over the place. Some cells are over charging and I have to disconnect that cells charger. And other cells are turning off early. The problem is each charge or pack is different. Yesterday they charged pretty well. But today it's a PITA. So I am looking to build a set of 8 of these and plug into my balance plug while using my bulk charger.

I just hope they understand my question about using them in parallel while the pack is in series. Your better electrically so please give me your thoughts on these. Please note the current bleed is adjustable via jumpers.

http://www.szsmartec.com/EN/productsview.asp?PID=752

Bob

dumbass said:

Jeff,

Take a look at theses. I was quoted $2.60 each from the supplier. Note they are cell bleeders and not chargers. I was told they can be used in parallel while the pack is wired in series. I am looking at these because I am having problems with the single cell chargers actually balancing the cells properly. I find that while charging 8 cells (each with it's own 3,6v 2a single cell charger) the cell voltage is all over the place. Some cells are over charging and I have to disconnect that cells charger. And other cells are turning off early. The problem is each charge or pack is different. Yesterday they charged pretty well. But today it's a PITA. So I am looking to build a set of 8 of these and plug into my balance plug while using my bulk charger.

I just hope they understand my question about using them in parallel while the pack is in series. Your better electrically so please give me your thoughts on these. Please note the current bleed is adjustable via jumpers.

http://www.szsmartec.com/EN/productsview.asp?PID=752

Bob

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Geez never seen separate balance boards before, throw away price 8)
Each of those 39 ohm resistor's across a cell, should be around 0.3W dissipated in each resistor.
Trying to work out how they get those current values?
I see there is a few other components on board, but no circuit diagrams.
Possibly a voltage sensing chip, controls the bleeding process?
That would be a very cheap option, per cell.
I can't find any operation details or specifications!!

I had a very similar problem to you when charging, the voltages are all over the place
Maybe you have mismatched cells in your packs like me?
As you're only charging at under 0.5C, I would think a BMS might be a better option.
I had a 'evassemble' capacitor BMS on my pack for a while, charge/discharge, but it got smelly after a while.
I was sucking about 4C, out of the battery, on my gokart, so I don't think it could keep up with shuffling the charge around and smoked a channel.
Hope you have more luck with the charge bleeding.
My manual resistor balaning was burning my fingers Ouch.

Cheers Jeff

This is the way both my packs have acted since I built them from new cells. And strangely the fastest charging cells or even the slowest charging cells are not always the same cells like one would think.

My cells are prismatic cells with screw connectors. A long time ago I tried using the small individual cell bleeders that mount directly on top of the cell between the pos/neg screws. I think they were around 85ma bleed but not sure and cost $8 a pop. They did nothing even when I mounted 2 of them to a cell. I sent them back for a refund. That's why I was so interested in these bleeders. They have a very high max bleed rate.

Friday I sent the supplier an email asking if they except PayPal. I'm hoping to hear back from them by Monday. If they do except PayPal I will order 20 of them. That will give me 4 spares to burn.

Bob

dumbass said:

This is the way both my packs have acted since I built them from new cells. And strangely the fastest charging cells or even the slowest charging cells are not always the same cells like one would think.

Click to expand...

Same here.
I think with the low resistance of these cells, even the connections and cabling may cause issues too.
Are all the connections and cabling to your individual chargers similar.

dumbass said:

My cells are prismatic cells with screw connectors. A long time ago I tried using the small individual cell bleeders that mount directly on top of the cell between the pos/neg screws. I think they were around 85ma bleed but not sure and cost $8 a pop. They did nothing even when I mounted 2 of them to a cell. I sent them back for a refund. That's why I was so interested in these bleeders. They have a very high max bleed rate.

Click to expand...

Hope you have better luck with the new setup.
Now spring is here, I'll have to revisit my packs.
Hopefully, still alive.

megacycle said:

dumbass said:

This is the way both my packs have acted since I built them from new cells. And strangely the fastest charging cells or even the slowest charging cells are not always the same cells like one would think.

Click to expand...

Same here.
I think with the low resistance of these cells, even the connections and cabling may cause issues too.
Are all the connections and cabling to your individual chargers similar.

dumbass said:

My cells are prismatic cells with screw connectors. A long time ago I tried using the small individual cell bleeders that mount directly on top of the cell between the pos/neg screws. I think they were around 85ma bleed but not sure and cost $8 a pop. They did nothing even when I mounted 2 of them to a cell. I sent them back for a refund. That's why I was so interested in these bleeders. They have a very high max bleed rate.

Click to expand...

Hope you have better luck with the new setup.
Now spring is here, I'll have to revisit my packs.
Hopefully, still alive.

Click to expand...

My cables (wiring) are all the same gauge but different length. I guess that might have an effect but not sure.

I did place an order this evening for 20 of the high amp bleeders. $2.60 each plus $40 for FedX shipping from China. I'm guess there will also be some kind of duty tax as well. But when my Bafang mid-drive was delivered I never got a duty billing.

Bob

dumbass said:

My cables (wiring) are all the same gauge but different length. I guess that might have an effect but not sure.

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Don't quote me, but these low IR cells, if the wire charging was thin and long and differing lengths, I'm thinking it could cause mismatch issues also, as well as dealing with mismatched cells, from differing batches.
Amberwolf might be able to shed more light on the subject.

dumbass said:

I did place an order this evening for 20 of the high amp bleeders. $2.60 each plus $40 for FedX shipping from China. I'm guess there will also be some kind of duty tax as well. But when my Bafang mid-drive was delivered I never got a duty billing

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At the price for the boards, that sounds good, hopefully Chinese mate puts value on box as $1 gift LOL.
Be good to see the new 'little bleeders' (word used a slight, in the UK :wink working, can you keep us updated please. Cheers.
Got a meeting tonight with a new mate for knocking up some mean machine bikes.
He's mad about it as I am, except he's got the mechanical genius and machinery to match.
I'm just supplying some years of electrickery, being much helped and honed from collaborating on the ES with your good selves.
Cheers Jeff

A quick update on the individual bleeders I bought (and finally received!). I did a very crude quick test on them this morning. First off let me explain they are actually built as a (2 pack). Meaning the board contains 2 individual units sitting side by side. Each having a pos + and a neg - . Convienuntly, the pos of one unit is right next to the neg of the other unit. It's your chose to leave them connected together as a 2 pack or snap them apart (very easy to do). I chose to leave them together and use only 3 connection wires to connect to 2 cells. By luck my 2 fastest charging cells were #1 and #2. So the unit are individually isolated. Anyway, I started charging the pack with my smart charger at 6a. When the first cell (#1) hit 3.65v I pulled the plug. I connected the cell bleeders to the 2 highest voltage cells and started the charger again. At 6a and with the charger in the auto mode turning on and off the cells would now top out at 3.6 to 3.61v then drop back to about
3.5v and sit for awhile then start climbing back to the 3.6v range again. This went on for as long as I kept the charger running. Because I only had 2 cells protected at this time I only did this for a short time while the othere cells were catching up.

I also did the same test using an SLA charger with a max output of 28.2v @ 2a. I found the response time of the bleed off was much faster. Meaning it never over shot the 6.0v.

Keep in mind I only setup the test on 2 cells not the complete pack. And I was using pinch clamps with the wires wrapped and taped around the ends ( told you it was a crude test!). Next step is to build an 8 pack of these with Anderson connectors so I can plug directly into my balance plug setup on the pack. One thing to remember, these puppies are set from the factory to bleed at the max rate (1.7a). So they do get warm and they recommend using 18g wire. If doing it my way with jumpers or only 9 wires for all 8 cells I would think the wires should be upgraded from the 18g as they recommended.

BTW, the total cost for 20 units was $2.60 per unit, $4.00 for using PayPal and $40 for DHL international shipping. I paid no custom fees. So a total of $96. I purchased directly from the manufacture. But yesterday I saw a place (still in China) selling them for $1 each. So if you trust them that's a real bargain.

The 2 pack board measures 5/16" x2 7/16"x 4 3/8". I intend to put 4 or maybe 8 twin pack boards into a box (stacked one on top the other). So I will be leaving 1/2" to 3/4" between the boards and using a cooling fan. Because I am never in a rush with my charging and always charge 2 24v packs at a time I will likely use one 24v charger at 6a and split it with 2 connectors and charge 2 packs at the same time on the one charger. But of course each cell will have an individual bleeder.

Bob

http://www.szsmartec.com/EN/productsview.asp?PID=752

dumbass said:

http://www.szsmartec.com/EN/productsview.asp?PID=752

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Sounds like they are working well Bob 8), 1.7A is a decent bleed current too.
Are you leaving them permanently connected?
They probably specify 18AWG for volt drop purposes, big for 1.7A, as the difference between fully charged and over charge voltages are millivolts, is affected by size and length.