Best Battery Charger / Conditioner ?? Help wife is gonna kill me

I bought 3 of the hitec x4 chargers. Actually it was one x4, one x4 eighty, and one x4AC plus. You're right about the discharge time. These will discharge up to 1A but I used the .7A rate because I didn't want to experiment. I have since talked to someone who discharges at 5 or 6 amps but I'm not sure what kind of charger they used. I am ready to install my batt pack now. If everything works correctly I plan on selling the 2 DC powered chargers and keeping the AC/DC powered one. Other than the time involved I was pretty well pleased with the chargers. I did have issues with some of the batteries. I had to run several cycles on a few of them but I believe it was the battery and not the charger. I think I spent $125, $150, and $225 respectively. I also bought the USB adapter for the computer but never opened them. Just didn't take time to download the software from Hitec. I think the're pretty good for the money.

 

SEaton, it is better to overthink than underthink ... especially in this context!

I was thinking through the same purchase decision a couple of weeks ago. You are asking the same questions was. I ended up buying 4 of the Supermate DC6 due to the low cost and their popularity here on Priuschart ... I figured it would be easier to get questions answered.

Having read through some postings here and on the RC forums, it appears many of the single chargers (e.g. iMax B6, Supermate DC6, Thunder whatever) are nearly identical. Even the Hitec seems to have a similar user interface and is seemingly 4 of these single units integrated into one unit. I was initially a bit leery of the quad chargers due to fears they may not dissipate the discharge heat for 4 batteries as well as 4 separate units in similarly sized packages, e.g. the DC6 or iMax. Having said that, 1 of my DC6 died (during discharge) and mushatsu has also had a failed DC6. I have not read of any Hitec quads dying.

As you note, the time limitation on these is due to the relatively low discharge capacity. The DC6 (and many others) can dissipate up to 5W. For our voltage (i.e. number of cells), this works out to a 0.7A discharge rate. I don't know about the Hitec (as greasemonkey uses) but the firmware in my DC6 will not allow a higher discharge current for this setup. (For battery packs with lower voltages, it will go up to 1A.) Discharging 6.5A at 0.7A takes a bit over 9 hrs. I have been playing with the idea of modifying a DC6 charger to discharge faster (using external load/heat sinks) but that's a whole other topic.

These RC chargers can typically charge at a max of 50W or 5A. This is not much of a limitation in our context. 5A represents a charging rate of 0.77C and I wouldn't want to go much over 1C (6.5A). A 5A rate works out to 1.5 hr charging but it will take a bit more due to the overhead of the delta V readings ... maybe 2hrs max.

In prior work, I have had access to the professional chargers that can discharge much faster. The cost is so much higher that you could buy 4 DC6 or one Hitec for less. While the professional charger would go faster, you would be needing to move it from one module to the next more often. For most DIYers, it is more convenient to buy multiple chargers, set them up on several modules, and come back every 1.5 to 2 days to switch to a different set of modules. (Also, you will probably get more help here if you are using the consumer-grade RC chargers.)

As for other eqmt, I fabricated a few cables but that is not entirely necessary. (The chargers comes with cables that have alligator clips. I prefer more stable connections ... if you consider yourself ADHD and have some electrical background, I expect you will feel the same.) If you buy chargers that require a 12V input, you will need some type of power supply. Do a power budget to ensure whatever you choose can supply adequate power. (PC power supplies and 12V car batteries seem to be most popular here. I am using a car battery that has a 'maintainer' charger on it.)

/Marc

 

Yes, those are the correct battery capacities. The batteries can safely be discharged at a much higher rate. With the monitoring software on a running Prius, people report on the order of 50A continuous and up to 100A as a peak. So, you can discharge at much more than 1C. As for conditioning the battery, higher currents are used (optimally pulsed) in other technologies to break up crystals. That is not such a problem for NiMH but for many of us it might be ingrained to charge quickly for this reason. In any case, charging efficiency is better for NiMH at higher charge rates. For example, 90% efficiency is typical at 1C in the mid-part of the SOC whereas 70% is typical at (1/10)C. That wasted energy is heating the battery so I don't think you are doing it any favors by charging it so slowly. I have not heard of using (1/10)C as a threshold except for trickle charging without a good cutoff mechanism, e.g. delta V.

0.9V is considered typical for a discharged NiCd cell. 1.0V is considered discharged for most NiMH cells. Many chargers default to these values and battery specs often use these values, e.g. http://www.gpina.com/pdf/6GP7PVS_DS.pdf

Correct though I would not say they give a projected capacity. However much is discharged on the last cycle is the capacity of the battery at that time. My chargers (Supermate DC6) do not measure internal resistance. This is usually done with an ammeter, voltmeter and a load. (If you use a bulb, note that it has a variable resistance meaning you must derive the battery resistance from current, open-circuit voltage, and loaded voltage.)

Regarding the discharge, yes. I have been thinking similarly of going 'off-script' relative to what is typically done on this forum. The primary advantages to using the chargers to discharge the battery are (1) it is automatic so you don't need to worry about over-discharging; and (2) you have the capacity recorded. If you do decide to do your discharges manually, I would recommend that you not discharge all the way as you need a consistent discharged level before you start a charge cycle. (The charging only puts a set amount of energy in the battery relative to its current SOC.) You might manually discharge to something in the 6.25 to 6.5 V range. Then, have the charger take over so it discharges to exactly 6.0V.

I agree with your reasoning but let's run some numbers to make sure I fully understand. For the standard method, the first discharge will be from a SOC in the 50% range so it takes on the order of 4 hrs. Then, you have 2 full discharges (~9 hrs each) and 3 full charges (~2 hrs each). Total 28 hrs. With your suggestions and an effective 3A load, these values would be (approximately) 1 hr initial discharge, 2 hrs second discharge, 9 hrs third/final discharge, and 2 hrs for each of the 3 charges. Total 18 hrs. You would be saving 10 hrs/module (at a cost of more babysitting). Correct?

 

Good point regarding doing these things in parallel ... you almost cut the time in half.

If you do decide to do this piecemeal, note that you might not want to charge all the way on your last iteration. You might save another ~hour per module. (You wouldn't get the cell-balancing benefit of that last full charge.) There have been other posts where people have put a fully-charged pack in their car only to get an 'overvoltage' error since the Prius is expecting to keep the pack between 40 and 80% SOC. Britprius recommended that I discharge my pack some (manually) after the final balancing (i.e. when all the modules are tied together) to avoid this problem.

I just noticed (after seeing your mention of 38 modules) that you have a Gen1 so I understand you have even more reason to try to speed the process. I think it is good to see the arithmetic as a sort of mental CRC but note that you will probably need to run more than the 3 cycles on several modules. It is hard to gauge how many until you have taken a measured discharge. I plan to go beyond 3 cycles on about 1/3 of my modules. (My pack is in pretty good shape with no dead cells. My goal is to get them all back to at least 6.0 Ahr.)

If you do build a discharger using power resistors or similar, be sure to post the design, pics, and your results.

 

This is communications with a seller on ebay where I was looking to buy some gen3 mods to put in my batt pack. Oldest ones are at the the bottom.

Dear greasemonkey347,


2nd gen is better for your case, and is cheaper.
I'm doing same, but using 6A charge, 6A discharge, which shows low capacity if discharged with 0.7A
But some of the cells does not increase the capacity after cycling.


- hybrid.parts
Click "respond" to reply through Messages, or go to your email to reply





From: greasemonkey347
To: hybrid.parts
Subject: Re: Other: greasemonkey347 sent a message about TOYOTA PRIUS HYBRID BATTERY CELL MODULE 2010-2012 fit 2001-2003 2004 2005 2006 #251350144738
Sent Date: Nov-11-13 03:44:23 PST


Dear hybrid.parts,

I used a Hitec x4 charger to discharge at .7A and charge at 5A for 3 cycles. I set the capacity shut-off at 7250mAh and the safety timer shut off at 660 min. The display on the charger records the charge and discharge capacities. The ones that were in the 4500 to 5500 range I ran for a couple more cycles and got them up to around 6000mAh discharge. Someone told me I would be better off getting gen2 batteries to keep them closer in age and capacities and the gen3 battery might be just a little bit bigger in physical size. My car is an 06 with about 140k miles. I've got 5 or 6 that I'm going to cycle again and try to get up to the 6000 mark so they'll all be pretty close to equal in capacity. Any suggestions are always welcome. This is my 1st hybrid to work on.
Thanks,
Charley

- greasemonkey347


From: hybrid.parts
To: greasemonkey347
Subject: Re: Other: greasemonkey347 sent a message about TOYOTA PRIUS HYBRID BATTERY CELL MODULE 2010-2012 fit 2001-2003 2004 2005 2006 #251350144738
Sent Date: Nov-10-13 19:56:16 PST

Dear greasemonkey347,


Charging/discharging is not a balancing. They are tested with 3 times charging/discharging and this help the capacity to be increased.
How did you measure the 5500-6200 capacity - what charge / discharge current. That's is pretty new batteries only.
Capacity depends of the charging / discharging current. We have all kind - from 4.5 to 6.5Ah.
A car at 80k miles 2007 has usually 4.8-5Ah
Thanks
Nick


- hybrid.parts


From: greasemonkey347
To: hybrid.parts
Subject: Other: greasemonkey347 sent a message about TOYOTA PRIUS HYBRID BATTERY CELL MODULE 2010-2012 fit 2001-2003 2004 2005 2006 #251350144738
Sent Date: Nov-09-13 19:23:15 PST

Dear hybrid.parts,

Have these batteries been balanced (discharge/charge 3 cycles) and tested checking the capacities and resistance? I saw that on the gen 2 listing. I've just did my battery pack and I need 1 mod but want to buy two. My capacities are in the 5500-6200 mAh range. I plan to work on the lower ones to get them all around 6000 or so.

- greasemonkey347





TOYOTA PRIUS HYBRID BATTERY CELL MODULE 2010-2012 fit 2001-2003 2004 2005 2006
Item Id: 251350144738
End time: Nov-30-13 07:01:20 PST
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"Charging/discharging is not a balancing. They are tested with 3 times charging/discharging and this help the capacity to be increased."

Thanks for the info greasemonkey. As SEaton, I question this statement. Perhaps the ebay seller is using different nomenclature and considers "balancing" to be only the process of equalizing the voltages across multiple modules. SEaton, I do not think people in general (or on this board) would say that calling the charge/discharge cycling "balancing" is incorrect.

The charge/discharge cycles do a couple of things. On the charge side, we are actually 'overcharging' the module. In normal operation in the Prius, the battery pack stays in a middle-point in its SOC capability. Gradually, stonger cells will take on more of the charge while weak cells (e.g. those that have lost electrolyte due to heating) will lose capacity. Overall, the SOC remains at the midpoint but at the cell-level some are charged to near capacity while some are taking on much less charge.

As a specific example, suppose a module (6 cells) has 1 weak cell that cannot hold any capacity and that we were able to charge a single module. If the other 5 cells (healthy) are charged to 90%, then the module can still attain a 75% charge which appears healthy enough at the module level. The bad cell is never forced to take any charge. As the healthy cells take on more charge, they take on more heat (due to lower charging efficiency as we near 100% capacity) meaning they will gradually weaken. (This is a contrived example for explanation purposes.)

By charging the module to its full capacity (which may be a bit beyond its specified value), we force all the cells, including the weak ones, to take on charge and restore their capacity. The repeated charging balances the cells against each other within the module. Note that the devices we are using are termed "Charger/Balancers."

An even better way to balance modules (battery packs) is to charge each cell individually (either directly or indirectly). That is effectively what these charger/balancer devices do when using the "balancer" boards with lithium batteries. (RC lithium batteries typically provide access ports to each cell so they can be balanced.) Ideally, we would have such access ports to each cell in our modules so we could do the same.

A high discharge rate can break up crystals but these are more of a problem with Cadmium. I would term that 'conditioning.'

In summary, I disagree with the ebay seller's comment that cycling the modules is not balancing them. I would ask some of the experienced board members to comment.

 

That is more elegant (soldering job notwithstanding) than what I was considering. I was considering simple power resistors with, effectively, a 6V regulator tied in to prevent over-discharging. That would have the obvious problem that the current would gradually decrease during the discharge

In your pic, are those regulators rated at 1A max each (total of 6A)? I see where the inputs pins are tied together and that the adj/gnd pins are tied to the output on each regulator. However, I cannot see where the gnd pins are tied together (as I am expecting). Maybe everything is grounded to the case?

I have a handful of LM1086 adjustable regulators (1.5A each) that have been sitting around ... maybe I have a use for them now!

 

Thanks for the schematic ... pretty simple. You are correct that those devices are typically 1.5A max current in the TO220 package. Good luck and I look forward to seeing your results.

Don't you hate that the discharge methods all just dump the energy into heat? Wouldn't it be nice if we could feed it back into charging some other battery? Besides not wasting the energy, the discharge would no longer be limited primarily by the heat dissipation.