Which discharger do you like guys?

[chilly81]

If you end up going down the route of having a larger LiFe battery as a field charging power supply, you don’t need a discharger. Most mid range chargers will support discharging to another battery. So you can drain your Lipo’s into your big field pack as fast or faster than dedicated discharges. Doesn’t make financial sense to buy just as a discharger, but they are awesome for a Field charging power supply. Win-win.

 

[Jerold]

I dig the ingenuity!

Ended up with the fd200 and it’s pretty neat how you can monitor and control from your phone. Plus it drains 6s 6000mah from 4.2v to storage charge in only 15 minutes!

I have the SkyRC BD250.

This works great but has one of the annoyance which is it just drains until the terminal voltage is reached. The problem is that there is voltage droop on the battery and it's never at the actual final voltage that I want. If I want 14.8V I will have to set it to 14.5V or something to compensate, or just go to 14V and then charge the batteries back up to storage voltage. Of course this works better if I'm using lower current, but then I'm spending a long time draining giant LiPos.

Do you know if the FD200 (or others) are smarter and will taper the current draw towards the end to get better accuracy?

 

[Johnny b]

I prefer this model. He discharges all over the lawn and really FAST!

 

[Hector_Fisher]

I prefer this model. He discharges all over the lawn and really FAST!

View attachment 288658

Can you plug a battery in and have him do the lipo discharges as well? Can you connect to him via your phone via bluetooth??? That would be totally awesome.

 

[RedOctobyr]

I dig the ingenuity!

Ended up with the fd200 and it’s pretty neat how you can monitor and control from your phone. Plus it drains 6s 6000mah from 4.2v to storage charge in only 15 minutes!

That sounds awesome! My big packs are "only" 6S 4100mAh by comparison. I have a better discharging setup. But one time, for simplicity, I used my smaller charger with 20W discharge capability, and it took a long time to bring down just a single battery. And bringing down a 3S 5000 on the Traxxas charger that I had temporarily (unsure of the discharge rating, possibly 5W?) took even longer

200W, and user-friendly, sounds like a great combination!

 

[jkflow]

I have the SkyRC BD250.


This works great but has one of the annoyance which is it just drains until the terminal voltage is reached. The problem is that there is voltage droop on the battery and it's never at the actual final voltage that I want. If I want 14.8V I will have to set it to 14.5V or something to compensate, or just go to 14V and then charge the batteries back up to storage voltage. Of course this works better if I'm using lower current, but then I'm spending a long time draining giant LiPos.

Do you know if the FD200 (or others) are smarter and will taper the current draw towards the end to get better accuracy?

Using the same one, yes, that is simple electric reality. Easy to calculate though, and I've placed a little sticker on it to get the right values.

Now keep in mind that a GOOD storage range is 3.75 - 3.85V i.e. you do not gain anything by being picky on 3.8V. It's just hammered into our mind because people keep repeating what they read and never go back to basics.

Drain away!

Also doing the LifePo solar battery thing myself.

 

[Hector_Fisher]

Using the same one, yes, that is simple electric reality. Easy to calculate though, and I've placed a little sticker on it to get the right values.

Now keep in mind that a GOOD storage range is 3.75 - 3.85V i.e. you do not gain anything by being picky on 3.8V. It's just hammered into our mind because people keep repeating what they read and never go back to basics.

Drain away!

Also doing the LifePo solar battery thing myself.

View attachment 288673

What are your thoughts on the need to balance cells after a discharge? I think in a perfect world, i would just drain them down to whatever I set the discharger to and call it good, all cells would be at the same voltage. However, practice has told me that this is not the case. Every battery is slightly different, but the voltage cell by cell can vary some after use, particularly when the cell IR varies slightly (3.5, 3.8, 4.5 mOhms on a 3s pack for example).

Now my buddy and I disagree on whether this is important to do, but I generally drop voltage down slightly lower than 3.8v per cell so that I can storage charge back to 3.8v in order to achieve balanced cells. He just drains them to his desired total voltage and calls it good.

Perhaps this is more of a question about how different the various cells can be off by and if there are long term consequences storing them like that.

 

[Jerold]

Using the same one, yes, that is simple electric reality. Easy to calculate though, and I've placed a little sticker on it to get the right values.

Now keep in mind that a GOOD storage range is 3.75 - 3.85V i.e. you do not gain anything by being picky on 3.8V. It's just hammered into our mind because people keep repeating what they read and never go back to basics.

Drain away!

Also doing the LifePo solar battery thing myself.

View attachment 288673

That's a good solution. It will change a bit with the discharge rate, battery size and age. Maybe I can do the same and put a sticker on the battery.

BTW I totally agree 3.7 or 3.75 V or 3.8V is pretty much all the same. Each device has a slightly different values and the battery voltage will change a bit based on heat and age. So I aim for the middle and call it a day.

 

[Jerold]

What are your thoughts on the need to balance cells after a discharge? I think in a perfect world, i would just drain them down to whatever I set the discharger to and call it good, all cells would be at the same voltage. However, practice has told me that this is not the case. Every battery is slightly different, but the voltage cell by cell can vary some after use, particularly when the cell IR varies slightly (3.5, 3.8, 4.5 mOhms on a 3s pack for example).

Now my buddy and I disagree on whether this is important to do, but I generally drop voltage down slightly lower than 3.8v per cell so that I can storage charge back to 3.8v in order to achieve balanced cells. He just drains them to his desired total voltage and calls it good.

Perhaps this is more of a question about how different the various cells can be off by and if there are long term consequences storing them like that.

If just make sure they are all about the same. If you need to cell balance after discharge, it's probably important to understand why, it may indicate cell damage.

 

[Hector_Fisher]

If just make sure they are all about the same. If you need to cell balance after discharge, it's probably important to understand why, it may indicate cell damage.

I think you're looking at my response with the perspective of a bad cell. That's not what I'm driving at. You said to make sure they are all "about the same". But what does that mean? What if the cells vary by 0.010v after a discharge? 0.050v? 0.100v?

On a good day, after a balancing storage charge to 3.8v per cell, voltage in my lipos usually varies cell to cell by around +/-0.005v (for example something like 3.802, 3.808, 3.805). I would expect them to vary more so during a discharge to 3.8v per cell, because they will not be balanced during the discharge. In the same way, if I performed an unbalanced charge, should I expect them to differ slightly in voltage?

Clearly, balancing during a charge is essential due to the minute difference between cells. So why would it be any different for the variation between cells after a discharge?

 

[chilly81]

I think you're looking at my response with the perspective of a bad cell. That's not what I'm driving at. You said to make sure they are all "about the same". But what does that mean? What if the cells vary by 0.010v after a discharge? 0.050v? 0.100v?

On a good day, after a balancing storage charge to 3.8v per cell, voltage in my lipos usually varies cell to cell by around +/-0.005v (for example something like 3.802, 3.808, 3.805). I would expect them to vary more so during a discharge to 3.8v per cell, because they will not be balanced during the discharge. In the same way, if I performed an unbalanced charge, should I expect them to differ slightly in voltage?

Clearly, balancing during a charge is essential due to the minute difference between cells. So why would it be any different for the variation between cells after a discharge?

Because once they are discharged, you’re not doing anything with them. When they’re charged, you’re drawing tons of current and running the car around and taxing the battery. If they’re just sitting on your desk, imbalanced it doesn’t really matter except as someone else mentioned if it’s very different than your battery is probably just going bad. Otherwise, everything will balance out again when you charge them and you’ll be fine.

Also, it’s unlikely (not impossible) your voltage measuring device is calibrated and either accurate or precise to the millivolt level. Some have the ability but are not calibrated, some just aren’t good enough. I never look at anything past the second digit.

 

[Jerold]

I think you're looking at my response with the perspective of a bad cell. That's not what I'm driving at. You said to make sure they are all "about the same". But what does that mean? What if the cells vary by 0.010v after a discharge? 0.050v? 0.100v?

On a good day, after a balancing storage charge to 3.8v per cell, voltage in my lipos usually varies cell to cell by around +/-0.005v (for example something like 3.802, 3.808, 3.805). I would expect them to vary more so during a discharge to 3.8v per cell, because they will not be balanced during the discharge. In the same way, if I performed an unbalanced charge, should I expect them to differ slightly in voltage?

Clearly, balancing during a charge is essential due to the minute difference between cells. So why would it be any different for the variation between cells after a discharge?

What @Hector_Fisher said.

If you are off by 100mV (0.1V) it's not going to matter, i.e. 3.5/3.6V. When you see values of 3.802, 3.808, 3.805, that's pretty dang good.

It's important to check your cells after you run. The real problem is when you discharge or run it the battery, the LVC looks at the total voltage of all the cells. If you divide that by the number of cells, that is your LVC (average cell voltage) number. Let's say you set your LVC at 3.2 (yah it's really low). If all the cells discharge evenly(ish), it might look something like this when your done. This is fine, the battery is usable.

​

But if you have a bad sell the total might look like this. Where the total voltage and the average are OK, but you have one cell that is well below the 3.0V threshold.

Again if you see on that is way off (0.100V or more) then you might look into why that cell is being fussy. If it's 3.7-3.5V I wouldn't worry about it, but maybe keep an eye on it.

Also if have a bunch of batteries and they are all the same brand and capacity, it's worth labeling you batteries so they are unique. Like CNHL1, CHNL2, or however you want to. That way if you have a problem with CNHL4, you can make a note of that. If it reappears it might be time for CNHL4 to be retired.

 

[Av642]

Just to manage expectations, 200W of discharge, at 6S, is about 8A. It could only hit 25A at lower cell counts, like 2S.

My iCharger 308Duo allows discharging from one channel onto a resistive load on the other channel. Like light bulbs, for instance. I modified a cheap hair dryer to act as the load, I can put 500W+ (I think more like 700W) into the hair dryer, whose fan keeps the hair dryer from overheating.

More info on this please, I want to do this with my icharger x8.

 

[Jerold]

More info on this please, I want to do this with my icharger x8.

You can also buy high current resistors on Amazon.... Ok you can buy anything on Amazon.

Wire them in parallel to lower the resistance (faster discharge) when I need to kill a LiPo.
https://www.amazon.com/gp/product/B08D3GRMX4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I also added a Volt meter to watch the progress, and put it in a box with a 9V so it continues to work below 4.5V.
https://www.amazon.com/gp/product/B00BYKRETK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

My build of the Volt/Current meter.
https://www.arrmaforum.com/threads/panel-mount-xt60-female.52605/#post-759827

If you don't want to make the volt/current meter you can buy one.

https://www.amazon.com/Precision-Analyzer-Consumption-Performance-Backlight/dp/B0B8VWNY9X/ref=sr_1_1_sspa?crid=2B8MTSMUZB23U&keywords=RC+watt+meter&qid=1680156902&s=industrial&sprefix=rc+watt+mete,industrial,170&sr=1-1-spons&smid=A3GZUGKBRUI9VM&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzSDRMRkhERlBTTVc2JmVuY3J5cHRlZElkPUEwODg0NzU0Rk9NVEtTN1RHMjJKJmVuY3J5cHRlZEFkSWQ9QTA2NzM2NjgzUFNUQ1ZRTTFSOEVVJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1

You just need to make sure you don't exceed the wattage of the resistors. Although, even at 8S you can still use 2 of them in parallel. Then add more when the voltage drops.

If you want to build you own, the schematic is below. The notes are for 4S and I ended up with a 9V instead of 4xAA batteries for the Volt meter.

Edit: Added link to Volt/Current Meter build.