My Vectrix Lithium conversion

...
...

what this tought me is that we can put any source we want, as long as the voltage is higher than 120v, the MC will not slow down the motor no metter the SOC of the battery, we CAN use ANY KIND of battery as long as the charger is not sending SOC/LIGHT/TIMER CANBUS commands everywhere... i had entire range trips (yeah...29km) with no charger and it actualy went longer until the volgate-cutoff.
we defenatly need external charger(s) for a pack this size. i see no way (reprog?) the VX-1 charger will charge anything that it doesen't know. all the other parts will work for sure from other sources.
...
...

That is great news!

And welcome to the forum!

Thats a very interesting point Andy! has made, in that the shunts do need to be a similar resistance to a battery so the last ones dont get charged at a different rate. (the bat controls the votage!)...
...

It's also what I meant with my initial questions:

How do they do the 600mA shunting during charging? Does this cause a voltage drop which might confuse the charger?

As in: Half the cells have hit the cutoff voltage and are shunting (or 80%, 90% etc) - what will this look like to the charger?

Active balancers take excess energy from cells with higher Voltage and transfer it to the cells with lower voltage.

When my first battery pack died last year and I wasn't sure I'm gonna get another one, I was actively looking at a LiPo solution, using my experience from RC world (I fly RC helicopters). My battery pack consisted of 38 Kokam LiPo cells (sheets), which would make a perfect fit into the Vectrix battery bay with room to spare and a series of 3 Schulze balancers, which can be connected together in series to cover all the cells and they communicate with each other. They are powered by the cells they are balancing and actively balance the cells all the time - they transfer electrical energy from cells with higher SOC to cells with lower SOC. Their max. current is 5A of transfer (not heat dissipation!), so that should be enough for charging and discharging, since they only need to balance - keep the same level of SOC for all cells.

Edit: Like this one: http://www.schulze-elektronik-gmbh.de/LiPoProB-e.htm

Balancing the cells requires a constant current source and a system that can shunt the full amount of current (from the CC source). As a cell reaches 3.65V the shunt turns on and all the current goes around that particular cell. Typically the shunt is just a FET and a resistor. Since the drop across the FET and the resistance of the resistor will vary from cell to cell, the shunt turns on and off as the voltage of the cell fluctuates around 3.65V. There is no voltage drop seen by the charger as the voltage is simply maintained at 3.65V on the full cell. All the cells that are not yet full continue to charge at the CC rate. Its a slow process since the current rate is low. It is challenging to shunt the current even at low rates because you are basically creating heat. At a 300mA EQ current you need to dissipate 1W/cell..it can add up to alot of heat.

I can explain a couple of the queries above.

Firstly the battery controls the voltage, so if u put 10v of even 50v on a batt reading 3.3v the charger will be pulled down to the 3.3v
However the 50v system would charge the battery quicker!

So if the shunts are say, in my example 10ohms, and the internal resistance of batts 20 ohms

If you have 10 3.3v lifepos charging from a 40v source ....
when none are shunting they each are dissipating 3.3-3.65v each (in theory 4v but the batt pulls it down to its voltage)

when 9 are shunting the last one would 'theoretically' get 20/(90+20) of the pd, i.e. approx 7volts

But in reality the last battery will still pull this down to the 3.3-3.65v level, and will just finish charging quicker.

In a Nutshell - Nothing to worry about. The resistance of the shunts might have been a problem in theory, but it never is in Practice!

That's the 1 Amp you mentioned earlier?

That's the maximum safe limit that these can shunt. They are at risk of failure over that.

The shunts don't try to absorb more than 1A.
If more than 1A is going in, the cell voltage rises.

if the cell voltage rises to 4.2v, the "All good" signal from that cell module disappears (well it goes OC).

if the master is in the somewhere, it cuts mains power to the charger.

its fine to use the original Vectrix charger with a lithium pack.
the real trick is where at pack voltage = CP xxx, the pack isn't fully charged, the stock charger will just shut down.

BMS terminated charge is fine (it will do so if the original charger doesn't shut down first).
it just means the cells don't get the CV stage.
if the pack is reasonably balanced, the pack is fully charged anyway.

Matt

...
...

One thing I am still unsure about are the 3 voltage sensing wires on the temp prob board.

Do I need to hook these up on mt lithium cells or can I just delete them? I can divide a 44 cell pack in the same ratios as the 3 segments of the stock pack. If I need to connect them, can I use a slightly higher voltage but the same ratios between the wires?

How?

102/27 = 3.7777

44/3.7777 = 11.64

That may not be a problem, but I don't think you can easily get an accurate division!

Delete them.

Delete them.

Thank you for that information. I was wondering about that also, when I was considering 38 cells of Kokam LiPo pack, divided into 18:10:10.

So, what are they for?

Delete them.

Thank you for that information. I was wondering about that also, when I was considering 38 cells of Kokam LiPo pack, divided into 18:10:10.

So, what are they for?

I can tell you what they are not for (or not capable of): Even when you place the 13 worst cells into one of the 27 cell parts (as I have done), the stock system remains unable to notice any problem even when the first cell drops down the knee of the discharge curve to around zero volt or below. At least I did not notice anything.

The voltages of the 27 cell segments (and of the 8 and 9 cell modules) are very closely matched during charging and during riding when the battery is balanced. A few tens of millivolts difference only.

The innocuous looking little board is also very dangerous - there are (nominal) 95V DC across two of the solder connections on it! No fuses or resistors to protect it!

But the temp sensors for the rear battery are integrated into it, so you need to keep it.

You could try out what will happen quite easily - your warranty is void anyway if/when you are dropping a Li pack in:

Cut the cables to the three tabs, but not the ones to the temp sensors before changing anything else. If the Vectrix keeps functioning normally, then the voltage sensors are not needed. If it stops working, solder them back together.

Cutting the cables is of course dangerous - cut one at a time with isolated cutters, then cover the bare live end with shrink-wrap or something to keep it from shorting.

My little IMAX B6 charger cacked itself on the 3rd to last string of six cells :(

so now I have 24 charged cells, and 18 partly charged cells.

I am contemplating stringing all 7 groups of 6 series cells in parallel to let them self balance

Will that work?

You might get a phenomenal spark at the start!

Just get a new charger, you want one anyway......can anyone be without one?

I use a RT808D, not because of anything other than that it was available when I walked into the RC hobby shop. But they have moved or closed down....

Something called "Overloader 2" would be nice - let me know if you can find a source for one in Oz, please!

I am contemplating stringing all 7 groups of 6 series cells in parallel to let them self balance

Will that work?

No, no! Don't do that! What you need is a balancer. It's what I already described; maybe not in this thread but somewhere.

My little IMAX B6 charger cacked itself on the 3rd to last string of six cells :(

so now I have 24 charged cells, and 18 partly charged cells.

I am contemplating stringing all 7 groups of 6 series cells in parallel to let them self balance

Will that work?

just parrallel the partly charged cells and bring them up with a powersupply with a 3.6v voltage limit.

fail that, assemble the evpower bms charge those 18cells in series with a current limited powersupply.

personnally, starting with a full pack of discharged cells, I just assemble them with the evpower bms and let a string charger charge them up (with the master able to terminate of course)
when they come from the factory in the crate, they are pretty close together in terms of SOC (they even all have identical terminal voltages).

unfortunately, once you start charging individual ones, the first balance becomes a bit tedious.
lesson for the future, dont take the cells outta the crate until you are actually installing them.

Matt

Any news?

The photo shows that you do not have your cells clamped together, therefore you are in danger of cells swelling. Thunderpower advises that cells should be securely clamped together, between sturdy end plates, or swollen cells may result.--Bob

...
...

Been running this for about a week when I can go and check on it every 1/2 hour or so. There is no automatic charge cut off and I don't want to kill my new cells

Better get yourself a timer for a few dollars - for when the kids decide that mum and dad really want to go to the hospital with them right now.....then you will still have working cells when you come back home!

Living up to my handle I'm afraid :)

Actually, it's been a bit of a mad house here lately. The youngest two have decided mum and dad don't need to sleep at night. I work rotating shifts at a fair bit of OT (both days this coming weekend...)

Enough excuses. Here is where I am at:

I have a 4s10p pack, connected with building hardware (galv bracing strap) hooked up to a 4A car battery charger

Been running this for about a week when I can go and check on it every 1/2 hour or so. There is no automatic charge cut off and I don't want to kill my new cells

To procrastination inc (your picture shows a Car battery in parallel too (why?)
I'd say your lucky you used thin wire and a little 10 amp connector.
Linking the LiIronPOOOO's to a Lead Car Battery with could easiily been CAPOUF.
There is no current regulation between the energy in the car battery and the lithium 4series pack.
Same issue when paralleling any high power battery that could be at a different terminal voltage/potential.
(BE CAREFUL - Use a blead resistor/wire circuit first)

But maybe you knew this, and were just using the Car battery to regulate the charger output that can reach over 16V with small output current.

Also did you decide to keep the three voltage sensing hooked up?

I'm still laughing over the "Delete it" phrase about removing the sensing.

Are you going cycle them a few times with a discharge of say 1A for 10min then top up?

You might get this discharge by just turning off the charger and the LiIronPOOO's will blead through the Pb Car Battery.
It would be interesting if you had DC current meter between the Lead and LiIronPOOOO packs.

I see from your picture too that you have four Cell Monitors attached.
Could you use the alarm output to operate a relay to stop charging?

The photo shows that you do not have your cells clamped together, therefore you are in danger of cells swelling. Thunderpower advises that cells should be securely clamped together, between sturdy end plates, or swollen cells may result.--Bob

cells dated 2009 and later for both manufacturers have reinforced sides, overcoming this requirement.

you can still clamp, but it isn't necessary any longer.

Matt

btw - if you put all the BMS modules on those paralleled cells, the shunt current would be around 8A.

it should be sufficient to stop that automotive charger from overcharging any of the parrallel stacks.

Matt