The Zivan NG1 revealed

[Patrick]

Nope, I don't think that will work. The upper voltage is set by by the transformer installed for the nominal voltage. You can probably increase the voltage by 10% or a bit more, but you cannot take a 24 volt unit and crank it up to 80 volts. You can however, turn one down to any voltage you like (assuming you have the range in the control pots), but you won't recover the amperage of the lower voltage units.

In other words, there are models for each major voltage (24, 48, 72 and 96 I think), and you need to keep mostly to those voltages. The charge curve is micro controlled, and adjustable within the limits of the V and I pots.

 

[GGoodrum]

Patrick, what ever happened to the firmware upgrade for a LiFePO4-based profile?

 

[flashedarling]

Ahh I think I've got it now. I'll get a 72v NG1 if I can find one. The only problem being the charging curve. How much does Zivan charge for a IUa curve chip? I'm assuming that you can order one and install it yourself. I'm interested in what you've found out about re-chipping.

 

[Patrick]

Well, I dropped the ball on that re-chip process. I did talk to them late last year, saying I had several (yours among them, Gary) that I'd like to get re-programmed. The answer? "Sure, send them all in and we'll take care of it". Naturally, I didn't have them all, and I didn't want to send any in. I did send an email detailing the specifics, but never got an answer back. I myself I have a couple of Ni-Zn profiles, which are stupid enough I could slide by with manual tweaking and Garys' board. But now I need to order 3 of the BMS boards, so it's back to the drawing board!

Gary - I'm pretty sure I have the details we talked about, but maybe we could revisit them in light of the most recent design. I guess there are two approaches - use the intelligence in the Zivan to approximate a curve, and use the BMS to do all the heavy lifting.

Zivan approach: This will be an IUa curve.
1st stage: CC to 3.5 v/cell. So I1 = max (13-18 amps, depending), and U1 = 56 v (for a 16 cell pack). Timeout of 5 hours?
2nd stage: CV to 3.7 v/cell. So U2 = 59.2 v (for 16 cell pack). Should there be current limiting in this stage? Timeout of 2 hours?
a (auto-shutoff) stage: when current falls below 200 mA. This should work either with the BMS board, or without the BMS shutoff.

I'd like this to work with the most minimal BMS - what do you think?

BMS approach: This will use the Zivan as a straight current limited supply, and be targeted solely for the intelligent BMS board. It must be shown that the FET current limiting won't interfere with the Zivan measurements. It will need to shut off without error when the BMS trips and eliminates input current.

If it is possible (i.e., I can work it out with Zivan) I would think the most useful product for them to sell/stock would be a 72 volt unit, with the voltage setpoints selectable thought the external switch, so that a single supply could work for 16 - 20 cell (or perhaps a bit more) packs. It would limit max current to about 12 amps.

I'm looking for input here (from all who are interested), so feel free to post or send me a PM.

Thanks!

 

[GGoodrum]

The 1st stage is fine, full current until the pack gets to 3.5V x # of cells, but I think the 2nd stage should be to throttle the current back to about 5A, or so, until 3.7V x # of cells is reached, and then CV mode from that point (3rd stage?). Richard might need to chime in here, but I think that since the BMS board will start to take over, and throttle the current once the shunt thresholds are starting to be met, the Zivan should not terminate on the current dropping below a certain threshold (200mA, in your example...), but should probably just timeout after say, 3 hours. This should cover all but the most severely out-of-balance conditions, even for big Ah packs. If the charger times out before the BMS turns the green LED on full, the charger can just be recycled and it will get back to the same point pretty quick.

For the BMS control option, we could maybe use the same active low signal that we use to trip the SCR cutting off the charge current, to pull a line low at the charger. If it can read something like this, it can use it to stop the charge process. Otherwise, trying to do it just monitoring the current might be toughter. I suppose it could look for the current to go to zero for some period of time, like 5 seconds, or so.

I like the idea of having one 72V version, with selectable output settings, even with a 12A limit. Many people, myself included, have multiple setups with different pack voltages. BTW, this would work with 16-24 cells. Maybe they could do two versions, the 72V that can work from 48-72V, and a second one that could cover 24-48V, maybe with a bit higher current (15-18A?).

-- Gary

 

[flashedarling]

I got lucky and managed to snag one off of ebay for $300. It has the following sticker on it. "Micro Upgraded, I2 Increased, T3 Extended" Trojan : U1 85.3V : I2 4A : I3 2.6A : Ur 76.8V: Restart 7 day: 130Ah. I'm wondering if I can use this if I change the voltages but I'm not sure how to manage the Ur being lower than the U1.

So I'm emailing Greg to send me a new chip to get a better profile for LiFePO4.

I still have a stumbling block. What kind of plug do I need to connect to the DC out anyway?

 

[ScuderiaEV]

The Zivan NG-x battery chargers are very strange.

The power stage is nice, clean, and simple, but the control logic is odd. Despite being microprocessor based, it's very infleible with a hard coded charge curve (or set of curves) and fixed time-out periods. The CPU doesn't even know what the absolute voltage and current levels are, only the relative levels When you turn the adjustment pots, you're changing the value the CPU 'sees'. For lead acid, the equalise current is a fixed proportion of the bulk current.

Some time ago I reverse engineered the control card; http://www.compton.vispa.com/Old_NG3_logic.pdf

It would be a fairly straightforward task to install your own piggyback board in the CPU socket, but note you have to keep kicking the watchdog or it shuts down the digital pot.

I did design a new analog section (with the intent of adding a digital section later) but have yet to test it.

 

[VRdublove]

Shouldn't my charger cutoff power altogether once it reaches 100% SOC? The green LED illuminates at 100% SOC (when amperage trickles down to 2A), but the charger continues to trickle current into the battery. Is this normal?