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Hairdryer to discharge LiPos

Old 01-02-2015, 05:44 AM
  #26  
kyleservicetech
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Originally Posted by dereckbc View Post
Dennis, I have another expensive hobby, EV's. Nothing big or too fancy, even a little silly, racing golf cart. Well I could race it as not many golf carts can do what mine will like go 50 mph. May not sound fast to you, but trust me - to 50 mph in 5 seconds in a golf cart will scare the pi$$ out of you.

My point here is the cart uses lithium batteries, AC motor, controller just like planes. Just on a whole lot larger scale. Also a professional engineer who has worked with battery plants all my professional life.

What rate are you discharging the batteries? I would be a little concerned going more than 1 to 2C. Not because of fear of fire or safety, but battery life.

Granted these batteries are made to discharge at high rates does not mean it is good for them.
50 MPH Gulf carts? Hope you have seat belts!

Which batteries are you referring to, the Lead Acid types? I was discharging them at 40 Amps on a 120 Amp Hour deep cycle unit. At 40 Amps, that should be three hours total time, and at 20 minutes per charge cycle, around 9 flights. Brand new Lead Acid battery, I was getting 3 or 4 flights before the lead acid battery went flat. And, 6 months later, I was getting one or two flights. The Cellpro Powerlab 8 charger is was set up to charge a 12S2P A123 battery pack as a 6S4P pack with a charge current of 20 Amps.

The lead acid battery charger is a quality deep cycle battery charging unit that is set to a 6 Amp charge rate, with cut off at around 14.4 Volts DC.
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Old 01-02-2015, 07:12 AM
  #27  
solentlife
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The matter of fast charge / discharge rates has 'bored' many a forumite I reckon !

But here goes .... I am one who believes in gentle approach. Why subject a pack to high rate if not necessary. I accept that average charger is crap at discharge rates.

Life of a pack is not in my mind dependent on number of cycles, but on how hard those cycles are on it. I think we can all tell a story or two of using unsuitable pack in a model and its demise !. I suggest same for discharge methods.

Nigel
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Old 01-02-2015, 08:04 AM
  #28  
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Nigel, I'd say that in principal you are correct, high discharge rate do stress batteries. What you overlook is that the rates I'm achieving even with the hairdryer are actually very low.
If you fly batteries then you would have them discharged down to about 80% in 5 to 10 minutes and think nothing of it. Even my fast discharger takes 15 minutes to discharge down to 50% charge.. So that's something like a discharge rate that's only 25% of what you would have in perfectly normal flight, plus the discharger is a steady rate, no 'bursts' to put extra stress on the battery.

To put some actual numbers on it: To discharge a battery to 50% charge in 15 minutes is an average discharge rate of 2c. Given that these are all at least 40c discharge batteries are you seriously suggesting that I'm stressing them?

I simply don't buy it that discharging over the course of hours at a rate of a fraction of 1c is any better for them, there isn't a scrap of evidence anywhere to support that, sorry.
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Old 01-02-2015, 10:16 AM
  #29  
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JPF ... sorry I was not suggesting your method here was stressing them ... I was poor in my wording.

I meant more that pushing limits of packs unnecessarily ... which some others have proposed in other threads, usually on another forum.

Discharging a pack to storage in 15mins is much less stress than lot of us put on a pack in flight.

Nigel
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Old 01-02-2015, 11:28 AM
  #30  
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Sorry, my misunderstanding..

To be fair though on first glance it would be possible to exceed the discharge rate of smaller LiPos with this discharger. I will go to 40 Amps, so if you were discharging a small battery that might exceed it's discharge rate.

In practice though because I'm using the icharger to control the discharge it can never exceed the battery discharge rate regardless of how small the battery is. This is because if the battery voltage at any time drops to 3.85v, the icharger automatically reduces discharge current. So if you hook up a small battery the charger will self limit the discharge rate to well within the batteries safe limit.

This is another advantage of having the discharger controlled through the icharger. It makes discharging to storage totally foolproof, you just connect any battery and start the discharge, there are no settings to adjust to suit battery voltage or capacity and no need for low voltage alarms or timers.
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Old 01-02-2015, 12:44 PM
  #31  
solentlife
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No JPF.... why you sorry ? You are right.

Even with my lightbulb job - I can push a small or low c-rate pack past its safe rate regardless of voltage at that moment.

Nigel

Last edited by solentlife; 01-02-2015 at 01:38 PM.
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Old 01-02-2015, 01:19 PM
  #32  
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Originally Posted by solentlife View Post
Even with my lightbulb jib - I can push a small or low c-rate pack past its safe rate regardless of voltage at that moment.

Nigel
Again, that's the beauty of using the iCharger to control the discharge. It automatically adjusts to avoid pushing the battery's discharge rate. As you know any battery when pushed near it's maximum discharge will get a lot of 'sag' on the output voltage, the iCharger detects this and controls current accordingly.

As an example; Today i discharged to storage a 2s 1800 25c Zippy battery. The discharge rate was pre-set to 40 Amps, this in theory would be pushing that battery pretty hard. The iCharger automatically limited to 10A based on detected voltage sag, I didn't have to adjust anything.
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Old 01-02-2015, 04:53 PM
  #33  
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Originally Posted by kyleservicetech View Post
50 MPH Gulf carts? Hope you have seat belts!
Yep 50 mph, and i have the speed restricted via the controller by limiting RPM @ 5000 rpm on a 7000 rpm motor. Yep it has seat belts and Scardy Cat Handles to hang onto. .

Originally Posted by kyleservicetech View Post
Which batteries are you referring to, the Lead Acid types?
No Sir LiPo in excess of 1C
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Old 05-23-2015, 11:10 AM
  #34  
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plenty of good information here, I am looking to build a discharging device. Although the ICHARGER 4010 has 130W internal discharge, it is terribly slow for my 6s packs! Using the 1600w external discharge capability would be great!
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Old 05-23-2015, 12:46 PM
  #35  
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I have the ICHARGER 4010 capable for 1600 watt external discharge. I have 3S and 6S Lipos that I would like to discharge.

Would the resistor below be efficient and safe to use when switching between discharging 3S and 6S or would I need a resistor of unknown value for my 3S and another resistor of unknown value for my 6S Lipos.

I understand that 1 ohm is the most efficient for the ICHARGER 4010, as this charger is 40 amps discharge at 40V

The resistor below is one that had been mentioned back a few posts for 31 amps continuous. Could anyone recommend a resistor that would safely enable me to get 40 Amps.

http://www.digikey.com/product-detai...574-ND/2367679

People are using converted hairdryers but this is too noisy for me!

Last edited by NHENRY; 05-23-2015 at 02:54 PM.
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Old 05-23-2015, 11:05 PM
  #36  
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Default Multiple Power Resistors

Originally Posted by NHENRY View Post
I have the ICHARGER 4010 capable for 1600 watt external discharge. I have 3S and 6S Lipos that I would like to discharge.

Would the resistor below be efficient and safe to use when switching between discharging 3S and 6S or would I need a resistor of unknown value for my 3S and another resistor of unknown value for my 6S Lipos.

I understand that 1 ohm is the most efficient for the ICHARGER 4010, as this charger is 40 amps discharge at 40V

The resistor below is one that had been mentioned back a few posts for 31 amps continuous. Could anyone recommend a resistor that would safely enable me to get 40 Amps.

http://www.digikey.com/product-detai...574-ND/2367679

People are using converted hairdryers but this is too noisy for me!
Yeah, it would be best to use multiple resistors for this function. At 40 Volts DC, and at 120 Watts for a power resistor, R = E^2/P which breaks down to a resistor of around 12 Ohms.

www.mpja.com has a 16 Ohm 120 Watt resistor available for around $7.00. So, with I=E/R, you get 40 Volts/16 Ohms, which is 2.5 Amps per resistor.

Or going to an 8 Ohm, 120 Watt resistor, you'd get 40/8 or 5 Amps per resistor. Power would be I^2*R or 5*5*8 or 200 Watts. Might be OK for a few minutes. It takes awhile for those resistors to heat up. You could likely operate them continuously at 200 Watts if you aim a high powered blower at them.

Getting 40 Amps would require 8 of those 8 ohm 120 Watt power resistors, all wired up in parallel. That would cost around $60 for getting your 40 Amp capacity.

Resistors of this size are pretty rugged as far as mistakes go, like hitting them at double their rated wattage. They are ceramic though, dropping one of them will result in cracking or shattering them.

These resistors run hot though, some 350 degrees F or so. If you have any little ones around, would be a good idea to put a protective shield around it.
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Old 05-23-2015, 11:28 PM
  #37  
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Default Another Option

Originally Posted by NHENRY View Post
I have the ICHARGER 4010 capable for 1600 watt external discharge. I have 3S and 6S Lipos that I would like to discharge.

Would the resistor below be efficient and safe to use when switching between discharging 3S and 6S or would I need a resistor of unknown value for my 3S and another resistor of unknown value for my 6S Lipos.

I understand that 1 ohm is the most efficient for the ICHARGER 4010, as this charger is 40 amps discharge at 40V

The resistor below is one that had been mentioned back a few posts for 31 amps continuous. Could anyone recommend a resistor that would safely enable me to get 40 Amps.

http://www.digikey.com/product-detai...574-ND/2367679

People are using converted hairdryers but this is too noisy for me!
Another option would be one of those hot water heater elements. They are designed to run IN WATER to cool them. At 1500 Watts, and 120 VAC, their resistance will be around 9.5 Ohms. With your 40 VDC supply, you'd be pulling around 4 Amps each. With a bucket of water, you could run a few of them as long as you need.

http://www.homedepot.com/p/Camco-150...5896/204220144
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Old 05-23-2015, 11:31 PM
  #38  
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Originally Posted by kyleservicetech View Post
Another option would be one of those hot water heater elements.

Good call. Plus you get the added benefit that you can make a nice cup of tea after discharging!

Last edited by JetPlaneFlyer; 05-26-2015 at 07:44 PM.
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Old 05-26-2015, 07:03 PM
  #39  
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Many thanks for your help kyleservice tech! You have been a great help!
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Old 05-28-2015, 04:26 AM
  #40  
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Originally Posted by JetPlaneFlyer View Post
The internal discharger in the iCharger 4010 Duo is the most powerful of any charger available (200W total or 130W per channel). But even so if i end up with a few 5000mAh 6s do take down to storage then it's still rather slow. The hairdryer is almost 10x faster plus it doesn't cause the charger to get hot like using the internal discharger does.

The hair dryer is controlled by the 'regenerative discharge' function on the iCharger, so it is safe. It stops when it reaches target storage voltage, just like if using the charger's internal discharger.
This may be a dumb question, but if your charger has a regenerative discharge function then why not just use it for what it was designed for; pumping the electrons back into your field battery? That makes more sense to me than simply throwing it away as heat.
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Old 05-28-2015, 05:58 AM
  #41  
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Originally Posted by FlyWheel View Post
This may be a dumb question, but if your charger has a regenerative discharge function then why not just use it for what it was designed for; pumping the electrons back into your field battery? That makes more sense to me than simply throwing it away as heat.
Simple reason - I don't have a field battery. I just have several LiPos that I charge at home. The field i fly isn't conducive to using a large field battery. It's a fair hike from the car park to the flying site and lugging a massive lead acid deep cycle isn't really practical and it's too far to return to the car to charge and as it public space not safe to leave my planes/heles etc behind if i do return to the car. Carrying the models and LiPos is bad enough.

If using a deep cycle then regenerative is a good option but you couldn't do it at anything even approaching the rates I can discharge at. A deep cycle would boil and probably explode if you tried to put 1000W charge rate into it!

It would be possible to use regen to storage charge the LiPos I've used using the 'spare' electrons I'm taking from the discharging batteries, but to be honest that's just a bit too much hassle and fraught with potential problems of over charging etc..
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Old 05-28-2015, 01:01 PM
  #42  
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OK that explain it rather conclusively.
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Old 05-07-2020, 06:35 PM
  #43  
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@JetPlaneFlyer

Rather old topic but..

I gues the Hairdryer you used is a 220V one?

I will pick up a 2200W hairdryer tomorrow.
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Old 05-16-2020, 12:59 PM
  #44  
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Originally Posted by Hobby4Life View Post
@JetPlaneFlyer

Rather old topic but..

I gues the Hairdryer you used is a 220V one?

I will pick up a 2200W hairdryer tomorrow.
Yes, it was 220V. Finding a hairdryer that is relatively easy to re-wind to achieve the desired resistance is the biggest challenge.
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