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Is it worth it to get dedicated Lipo Discharger? 2s discharge amps?

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Is it worth it to get dedicated Lipo Discharger? 2s discharge amps?

Old 07-18-2022, 07:38 PM
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Originally Posted by silence360
Got it all together and worked perfectly. So glad I was able to use what I had and make it work. Could have gone the resistor route but wanted to use the bulbs since I had them already. Storage discharged my 3s in no time. A bit nostalgic since I have had this deans discharge bulbs probably since 1995 or so.
Iím curious - you mentioned it storage charged that battery in no time. How long did it actually take? (Iím thinking of making something similar).
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Old 07-18-2022, 11:18 PM
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Originally Posted by RacingRookie27
Iím curious - you mentioned it storage charged that battery in no time. How long did it actually take? (Iím thinking of making something similar).
I just read several postings of you and wonder if you just react for the post count....

Discharging a full charged battery to storage mode takes about half the capacity of the battery. The time depends the load and the capacity which you can easily calculate.
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Old 07-19-2022, 09:31 AM
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Originally Posted by Roelof
I just read several postings of you and wonder if you just react for the post count....

Discharging a full charged battery to storage mode takes about half the capacity of the battery. The time depends the load and the capacity which you can easily calculate.
I'll rephrase my question - what's the current draw of a light bulb setup like that? I don't know how to calculate that load and am trying to learn.
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Old 07-19-2022, 10:09 AM
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Originally Posted by RacingRookie27
I'll rephrase my question - what's the current draw of a light bulb setup like that? I don't know how to calculate that load and am trying to learn.
Also that can be easy calculated.
A normal light bulb for the front lights is 50W at 12v. The drawn current is is 50/12 lets say 4A. Ohms law say the resistance is 12V/4A is 3 Ohm, so at lets say 7.5v the current will be 2.5A per light bulb.
But why light bulbs? Get some 100W resistors of 1 Ohm resistance, mout them on a heatsink with a fan, connect them parrallel and you did create a discharge bank without that irritating light.
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Old 07-19-2022, 06:16 PM
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Originally Posted by Roelof
Also that can be easy calculated.
A normal light bulb for the front lights is 50W at 12v. The drawn current is is 50/12 lets say 4A. Ohms law say the resistance is 12V/4A is 3 Ohm, so at lets say 7.5v the current will be 2.5A per light bulb.
But why light bulbs? Get some 100W resistors of 1 Ohm resistance, mout them on a heatsink with a fan, connect them parrallel and you did create a discharge bank without that irritating light.
Why light bulbs? Less heat to dissipate since most of the power is dissipated as light instead. I find fans more annoying than light bulbs.
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Old 07-19-2022, 08:14 PM
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Originally Posted by Roelof
Also that can be easy calculated.
A normal light bulb for the front lights is 50W at 12v. The drawn current is is 50/12 lets say 4A. Ohms law say the resistance is 12V/4A is 3 Ohm, so at lets say 7.5v the current will be 2.5A per light bulb.
But why light bulbs? Get some 100W resistors of 1 Ohm resistance, mout them on a heatsink with a fan, connect them parrallel and you did create a discharge bank without that irritating light.
Thank you
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Old 07-20-2022, 05:08 AM
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By the way the Red bulb discharger (the Deans brand one) uses 1157 bulbs that are rated at 2a each, and theres 10 of them so its supposed to be a 20 amp discharger if you fed it 12v. Its what we used in the nicad/nimh days. Wasnt quite 20a at 6 cell voltages but worked well. I dont have time to do the math, but Roelofs 50w 12v bulb isnt the same as the deans discharger.

Transporting them around every once in a while a bulb here or there would break and wasnt fun to repair. I much much prefer resistor dischargers, they can be much more compact and usually need a fan to cool but over all are a far better solution for most.
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Old 07-21-2022, 04:56 PM
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Originally Posted by gigaplex
Why light bulbs? Less heat to dissipate since most of the power is dissipated as light instead. I find fans more annoying than light bulbs.
+ nostalgia!
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Old 07-21-2022, 06:24 PM
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Somewhat off topic but am wrapping up building another smaller amperage discharger and was not planning on running a fan. After using it is apparent it needs a fan. - picture of someone else's discharger


Was going to just use a basic computer fan without the heatsinks as to me the resistor has the heat sink your trying to cool - why add more heat sink that has to heat up before you can cool it since the fan has no direct airflow to the resistors (these are heatsinks designed to cool processers so the bottom is not open)? Am I seeing this wrong? Also when your building these like that are you using a thermal paste paste


My 30 amp system has just a fan and works just fine but was wondering if there is any benefit to this style of heatsink/fan combo.....I only see downsides myself other then maybe increasing the thermal mass some..
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Old 07-21-2022, 06:56 PM
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Yeah I don't like those fans either, they are small and can be loud/high pitched.

I built my own 40a discharger with the same 100W resistors, but simply used the wire to hold them in a U shape and bolted them to an 80mm computer fan. It runs at a low rpm all the time and is quiet. And no extra heat sinks or anything. No pics, its ugly and I need to rebuild it. But just some bent aluminum and 3mm screws and nuts. I need to pickup some plastic to enclose it and make it nicer. Also going to add some feet so I can place it fan side down so it blows all the hot air straight up. Its pointed to the side and during the summer is not nice.

Well if I run stock classes and even want to use it, I run modified most of the time. Much easier when you dont need it. I'll try and fix it up soon and post pics though.
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Old 07-21-2022, 07:19 PM
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Originally Posted by sacmiata
why add more heat sink that has to heat up before you can cool it since the fan has no direct airflow to the resistors (these are heatsinks designed to cool processers so the bottom is not open)? Am I seeing this wrong?
The resistor has very little surface area, adding a heatsink creates more surface area. That'll improve the effectiveness of the airflow.
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Old 07-21-2022, 11:18 PM
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Originally Posted by Alexv2024
By the way the Red bulb discharger (the Deans brand one) uses 1157 bulbs that are rated at 2a each, and theres 10 of them so its supposed to be a 20 amp discharger if you fed it 12v. Its what we used in the nicad/nimh days. Wasnt quite 20a at 6 cell voltages but worked well. I dont have time to do the math, but Roelofs 50w 12v bulb isnt the same as the deans discharger.
Where can you find these light bulb dischargers new to buy?
It was just an example with today easy to get lights, the calculation is just basic Ohms law which in my time was a basic lesson at school.

And yes, the bulbs are fragile and still hot to handle, the resistors are more easy to use. Adding a heatsink is needed if you going to use them to the max or otherwise they will burn up. And a fan can be noisy but in the world of the PC's you can find all types of quiet fans and rpm and even temperature regulating controls.
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Old 07-22-2022, 05:15 AM
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Originally Posted by sacmiata
why add more heat sink that has to heat up before you can cool it since the fan has no direct airflow to the resistors (these are heatsinks designed to cool processers so the bottom is not open)?
The more heat sink you have the less amount of fan you need. It's theoretically possible to build one of these with no fans at all.
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Old 07-22-2022, 08:41 AM
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Originally Posted by mrreet2001
The more heat sink you have the less amount of fan you need. It's theoretically possible to build one of these with no fans at all.
I would generally agree with you and gigaplex - - more mass and more surface area is generally better for a heat sink and there are plenty of passive setups that do that just fine. I guess it comes down to how you want to engineer it....my 30amp is all fan - - was hoping with this one being designed around 7 amps that I could figure out a passive setup and avoid the fan altogether. ..... I might rethink how I do this one again!
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Old 11-16-2023, 03:43 PM
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Originally Posted by NZDave
I use a Skyrc BD250 and discharge my lipos at 10A. I take them down to 7.4V at 10A. This just makes discharging a whole lot faster than my normal charger. However it does not have a balance feature so may dis charge one cell more that the other. For this reason I would not put two batteries in series to discharge at once as you could finish up over discharging one of the packs. Once I have discharged my lipos at 10 amps on the Skyrc discharger I then put them on my normal charger to get to final discharge state.



Very sad to hear this discharger does not have balance feature, to balance battery voltage
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