Ricky_nz
10 kW
Those diodes drop about 1V at the currents you are talking about so for every 1A you put through them you will be dissipating 1W of heat. 35W wasted as heat is a rather significant amount.ProDigit said:
cap on battery, influences charging?
- Thread starter ProDigit
- Start date
This thread is so full of fail.
Firstly, don't parallell diodes. Secondly, diodes are not needed and should stay out of battery systems. Power waste and another possible failure point. The only thing you gain from it is a false safety feeling. Lastly, capacitors are made to counteract inductance - not for energy storage!
This is because the engineers do not know of the lithium batteries being able to do the same. They see "1 C charge", and such rule the battery not viable - even tho it might do 40C in bursts of a few seconds. Luckily F1 engineers aren't that stupid. I've seen the mechanical class do some stupid shit with electric motors, they should stay in their field - and let the power electronics engineers handle electrical systems.
Even Shane Colton had a ultracap on his "Cap-kart" for a small extra boost of energy (I think it was 16F). Had he added lithium instead he would have had a more economical and powerful solution - yet, idiocy like this you see from universites all the time. (This is not to bash Shane Colton, as he makes awesome controllers, just to make a point that much stupid shit goes down.)
Firstly, don't parallell diodes. Secondly, diodes are not needed and should stay out of battery systems. Power waste and another possible failure point. The only thing you gain from it is a false safety feeling. Lastly, capacitors are made to counteract inductance - not for energy storage!
texaspyro said:
This is because the engineers do not know of the lithium batteries being able to do the same. They see "1 C charge", and such rule the battery not viable - even tho it might do 40C in bursts of a few seconds. Luckily F1 engineers aren't that stupid. I've seen the mechanical class do some stupid shit with electric motors, they should stay in their field - and let the power electronics engineers handle electrical systems.
Even Shane Colton had a ultracap on his "Cap-kart" for a small extra boost of energy (I think it was 16F). Had he added lithium instead he would have had a more economical and powerful solution - yet, idiocy like this you see from universites all the time. (This is not to bash Shane Colton, as he makes awesome controllers, just to make a point that much stupid shit goes down.)
What he said.liveforphysics said:
Methods did so in his EV VW Bug, to get it home, IIRC.Punx0r said:I imagine so. I don't know if anyone has used Lipo yetneptronix said:Those are the guys who have a giant array of SLA batteries in the back of their car, right?
Only post I coudl find referencing it is here:
http://www.endless-sphere.com/forums/viewtopic.php?p=236730#p236730
but I know there is a whole thread about it.
etriker
100 kW
Did anyone at all read the Nasa tests ? I really like tests like that.
Not once in that test did they use the term c rate !
I guess that is why so little interest.
Some of you kids should stay in the puffy lipo threads and leave threads like this one alone.
This thread is not for group thinkers. It is for the kids that like to experiment and learn by doing.
I will tell you something about electronics too.
I have been fixing computers and tvs since the 80's.
The stuff changes fast and you have to keep up or get left behind.
Always learning and trying out new stuff. Always.
And techs that pretend to know it all don't.
Here is a link about using diodes on ebike packs.
http://www.endless-sphere.com/w/index.php/Paralleling_Multiple_Packs_and_the_use_of_Diodes
Who wrote that ?
I use different chemistries without diodes almost everyday.
Not once in that test did they use the term c rate !
I guess that is why so little interest.
Some of you kids should stay in the puffy lipo threads and leave threads like this one alone.
This thread is not for group thinkers. It is for the kids that like to experiment and learn by doing.
I will tell you something about electronics too.
I have been fixing computers and tvs since the 80's.
The stuff changes fast and you have to keep up or get left behind.
Always learning and trying out new stuff. Always.
And techs that pretend to know it all don't.
Here is a link about using diodes on ebike packs.
http://www.endless-sphere.com/w/index.php/Paralleling_Multiple_Packs_and_the_use_of_Diodes
Who wrote that ?
I use different chemistries without diodes almost everyday.
TylerDurden
100 GW
lol.Teh Stork said:
etriker
100 kW
TylerDurden said:
This is the test I linked to.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010069673_2001112722.pdf
Old junk broken screen plasma tvs are full of diodes and such to play with.
At 40A I have no other choice!Teh Stork said:
I'm talking about connecting an external battery of different capacity and make than the stock battery. I'm not using them within the battery system.
Any better solution than this? I can't simply plug in a battery in parallel with the main battery, especially if it's a different type, now can I?
Besides, if what you say is true, they will not dissipate 35w constantly. At acceleration all 4 of them may dissipate 40W of heat (which is really not that much! My laptop dissipates more heat). But while driving at a constant speed, I presume only a good 2-3A will flow through each of them (which translates in 8-12W, less than the light bulb of the blinker).
But if what you say is true, then perhaps it might be better to just use a diode on the extension battery, and not protect the main battery.
The only alternative is to find a 20-25Ah battery of 3-6V (basically a couple of cells in parallel), and put that in series with the existing battery; to increase the overall voltage. That would reduce the amps somewhat (or at the same traction there will be less amps, or at the same amps, there will be a greater acceleration).
It would work, only be a pain to charge them!
and why not? The gate is only for steering the flow. The flow goes one way, and there's virtually no voltage drop.
True, the gate needs a lower voltage than the main input, but one can either use a resistor to lower the voltage over the gate, or use a high power triode, (say one meant for 110/220V) that will allow 48V over the gate.
Now I would not use bulb-style triodes like on wikipedia. They're surpassed by solid state ones, that are far more efficient!
At this point, the guy making these 'ideal diodes' does not have them available yet.
Do these battery packs have a BMS?ProDigit said:
Is the fully-charged voltage the same on both packs?
Is the fully-discharged voltage the same on both packs?
If the answers are No, Yes, and Yes, then there really isn't a need for diodes. The main reasons they are needed:
--if the BMS of a pack has a problem with voltage being fed back into it thru it's discharge wire, because of a paralleled pack that is ever in a higher voltage state than it is.
--If one of the packs is a lower voltage than the other, and both are already at full charge. The higher voltage pack could then further charge the already-full lower voltage pack. In some chemistries, this could be a problem of one type or another; in others it just results in wasted power and heat.
--If one of the packs is a lower voltage than the other, and both are already at full discharge. The lower voltage pack coudl then further discharge the already-empty higher voltage pack, potentially causing damage of one type or another to it.
Otherwise the only thing a diode does (besides drop usable voltage at the controller and waste some power as heat) is to prevent the potential small waste of power due to charging inefficiencies, as a pack that discharges faster is recharged by one that discharges slower, assuming that this even happens in reality (vs theory).
I suppose there might be one around someplace, but I'm not aware of any actual solid state triode. You can make a FET *behave* like a triode, by doing something like this:
http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html
but a triode isn't the same as a FET or transistor. Effectively they can do very similar things, so I can see why you are using that term--but if you use a term that is intended for a functionally-different kind of electronics when talking about "modern" electronics, it's not going to help get your point across to most people.
I also don't know off the top of my head any common FETs that could handle 48V at the gate. Most are maybe 15V max.
I believe Tiberius here on ES used to make some, and there is a schematic in the thread that you could use to build your own.
Answer is exactly the opposite:amberwolf said:
yes, no, no
Both batteries have BMS.
Charging one battery will result in the second one being affected by it without Diode.
I don't even know if it's wise to charge both batteries at the same time, or if some kind of over-voltage could exist,
aside from the charging issue which I presume could be a problem, these batteries are not the same. In other words they do not discharge the same. And because they are such high power batteries, one battery discharging, could result in a large current flow to the other battery; not to mention what would happen if one (more powerful, say 49V 20Ah) battery would cause a current flow in the opposite direction of the weaker (say 47V 10Ah)battery.
Just speculating here...
My apologies. In my native language, the correct term would be 'triode', however I did not find a lot of reference to that word in English.I suppose there might be one around someplace, but I'm not aware of any actual solid state triode. You can make a FET *behave* like a triode, by doing something like this:
http://www.radiomuseum.org/forum/the_tr ... riode.html
but a triode isn't the same as a FET or transistor. Effectively they can do very similar things, so I can see why you are using that term--but if you use a term that is intended for a functionally-different kind of electronics when talking about "modern" electronics, it's not going to help get your point across to most people.
I also don't know off the top of my head any common FETs that could handle 48V at the gate. Most are maybe 15V max.
A 'triode' is basically a diode with a gate. I presumed (perhaps mistakingly) that the right word would be the same in English.
Otherwise, a triode is an excellent way to steer power; and instead of amplifying a gate signal (which it is mainly used for), one can also use it as a switch with very little resistance, I believe lower than a diode.
Unfortunately I'm not technically skilled enough to make them myself, unless there's some kind of parts box, and a user manual, and can be soldered easily.
If not, it would be beyond my league.
BatteryMooch
10 kW
Teh Stork said:
Caps are made for a very, very large number of uses. Surely you mean this only in a very specific set of applications, right? For example, e-bikes? There are billions and billions of caps out there doing nothing but energy storage without any regard for inductance.
CamLight said:Teh Stork said:
Caps are made for a very, very large number of uses. Surely you mean this only in a very specific set of applications, right? For example, e-bikes? There are billions and billions of caps out there doing nothing but energy storage without any regard for inductance.
Hmm - no. You can tie a red line back to inductance for most of applications where capacitors play a role. Sure, all the hobbyist uses for capacitors are pretty impressive - but that does not mean they're unique or especially good at what they're being used to. Our nano-tech powered can-crusher packed a bigger punch (it ripped the can to shreds) than the 1500VDC capacitor powered (and more expencive too!) cap-crusher another group built.
If you store energy, it's a battery. It's not like you call a car an apartment whenever it's being used as a home, even tho thousands of cars out there are doing nothing but work as a home.
Edit: well, after plundering more about capacitor role - I'll admit that only counteracting inductance is a too brave a statement - they're certainly used for many applications. Merely ment to point out that the role of the capacitor is to "smooth voltage" in most cases and that it, sort of, works exactly the opposite of a inductor. As for cap on a battery, no use - commercial chargers don't use them either, I've checked. You'll need a hell of a capacitor to make a difference.
etriker
100 kW
Teh Stork said:CamLight said:Teh Stork said:
Caps are made for a very, very large number of uses. Surely you mean this only in a very specific set of applications, right? For example, e-bikes? There are billions and billions of caps out there doing nothing but energy storage without any regard for inductance.
Hmm - no. You can tie a red line back to inductance for most of applications where capacitors play a role. Sure, all the hobbyist uses for capacitors are pretty impressive - but that does not mean they're unique or especially good at what they're being used to. Our nano-tech powered can-crusher packed a bigger punch (it ripped the can to shreds) than the 1500VDC capacitor powered (and more expencive too!) cap-crusher another group built.
If you store energy, it's a battery. It's not like you call a car an apartment whenever it's being used as a home, even tho thousands of cars out there are doing nothing but work as a home.
All circuits in Tvs and such run off of caps.
Before switch mode power supplies the caps were large and large transformers kept them charged.
Now switch mode power supplies operate much faster and can charge the caps faster so smaller caps and transformers can be used.
They are like a car battery that runs everything in the car and the generator keeps it charged.
The TV runs on the power stored in the output caps in the power supply and they are kept at the right voltage by pulses from the switch mode power supply.
Caps are like small batteries that need to be recharged a lot in power supplies.
That is what we are talking about here in this thread. Output caps in an ebike power supply.
In the NASA tests I linked to it worked but they needed about 80lbs of caps.
Then we were talking about using another battery, a smaller one that can charge and discharge fast like a cap.
Well, I agree to some extent with what you're saying - but I'd like to add that the capacitor only smooths the voltage, it doesn't supply the brunt of it. The 'TV' mostly uses energy straight from the inductor, the capacitors role is as much supressing transients around switching - as it is storing energy for use. Some multiphase buck-circuits are so sensitive that output caps can be omitted. Their line regulation can be held tightly withouth the need for a capacitor smoothing anything.
Edit: Caps in ebike-powersupply (as a part of the battery system), is still stupid. That NASA paper is not up to date. Compare it to modern day lithium, and you'd have a clear cut answer.
Edit: Caps in ebike-powersupply (as a part of the battery system), is still stupid. That NASA paper is not up to date. Compare it to modern day lithium, and you'd have a clear cut answer.
etriker
100 kW
Teh Stork said:
When they start to go bad and they do alot all kinds of problems happen.
Lots of the times we replace them with caps of a larger value.
I work on the new stuff from China everyday and have not seen a power supply without output caps.
etriker
100 kW
Teh Stork said:
The test is old and before c rates were invented !
I use small A123 packs for my main packs. They are the cells that I use for the output caps in my ebike power supplies.
Back them up and keep them charged with laptop cell extender packs.
TylerDurden
100 GW
Regarding the study indications: Proving 24V 12ah of SLA getting benefit from 65kJ of supercaps is like proving a slug moves faster when falling off a tree.
The hybrid-battery experiments ES members have shared indicate that high-power lithium secondary cells outperform supercapacitors in orders of magnitude, for mitigating voltage sag on high current demand.
I am far too lazy/buzy to track the links for this post. For the curious, suggest using search terms of supercap(s), maxwell, "hybrid battery", "boost pack".
The hybrid-battery experiments ES members have shared indicate that high-power lithium secondary cells outperform supercapacitors in orders of magnitude, for mitigating voltage sag on high current demand.
I am far too lazy/buzy to track the links for this post. For the curious, suggest using search terms of supercap(s), maxwell, "hybrid battery", "boost pack".
TylerDurden
100 GW
I will console myself with that notion, the next time I strap 86lbs of capacitors to an EV Global.ProDigit said:
The more I think about it, the more I believe a large cap on a battery is actually a good idea!
It evens out voltage spikes, it flattens voltage chops of the controller, and while charging, fights voltage peaks.
The only con is that a cap usually has a minimal current flow (in the range of a few uA to mA's, not enough to make a difference though).
I think a cap could actually extend battery life somewhat. However it's not beneficial if the cap costs too much money.
It would be ok if you could find a 60V cap in the range of 1F or more, for $10.
It does not take much space to install, and I think chances are it actually will prolong battery life (even if it's only little).
One thing though, the cap can not explode/short circuit. If it does, it could actually do more damage than good!
But usually caps last a long time!
I posted another reply that seemingly never got to the server (it never got posted to this thread).
In reply to Teh stork:
Caps are used for a variety of things, not only phase correctors.
They do help correct phase (on AC, not DC), but they could be used for signal filtering, and even voltage regulation!
With latest digital voltage choppers, it's quite easy to plug a cap behind the chopper, and get a regulated voltage (eg: input 10V DC, voltage chopper chops 25%, with correct cap you'd get something like ~3V DC on the output. With voltage chopper chopping off 50% of the flow, you could get ~5V DC on the output).
It evens out voltage spikes, it flattens voltage chops of the controller, and while charging, fights voltage peaks.
The only con is that a cap usually has a minimal current flow (in the range of a few uA to mA's, not enough to make a difference though).
I think a cap could actually extend battery life somewhat. However it's not beneficial if the cap costs too much money.
It would be ok if you could find a 60V cap in the range of 1F or more, for $10.
It does not take much space to install, and I think chances are it actually will prolong battery life (even if it's only little).
One thing though, the cap can not explode/short circuit. If it does, it could actually do more damage than good!
But usually caps last a long time!
I posted another reply that seemingly never got to the server (it never got posted to this thread).
In reply to Teh stork:
Caps are used for a variety of things, not only phase correctors.
They do help correct phase (on AC, not DC), but they could be used for signal filtering, and even voltage regulation!
With latest digital voltage choppers, it's quite easy to plug a cap behind the chopper, and get a regulated voltage (eg: input 10V DC, voltage chopper chops 25%, with correct cap you'd get something like ~3V DC on the output. With voltage chopper chopping off 50% of the flow, you could get ~5V DC on the output).
liveforphysics
100 TW
ProDigit said:
Where the hell do you get this sh*t? It's like every post you go out of your way to try to say as many wrong things as possible.
SamTexas
1 MW
More (many more) than one members have tried to say this without any success, and not just on this subject. Don't scare him away though, we all need the entertainment.liveforphysics said:
nicobie
100 MW
liveforphysics said:
Ever feel that you're talking to a brick? :wink:
BatteryMooch
10 kW
Teh Stork said:
I definitely agree that you need caps of several hundred farads or larger to make a difference in an e-bike app. Big, heavy, expensive and not worth it in that application IMHO. And you need HUGE cap banks for transportation uses (bus, railroad, etc.), but they are used. And (ultra)caps are used in parallel with batteries to provide better low-temperature performance than battery-only systems with pulsed loads. Even very high performance LiPo's lose a lot of their capability at low temps.
Additionally, small caps are used extensively in parallel with a battery in energy harvesting applications to provide the initial current burst to an intermittent load. This keeps the battery from having to supply all of this initial burst and measurably increases the battery's run-time since these batteries often have very high ESR and waste a lot of power if required to source current for larger pulsed loads. This is critical for remote sensors and other devices that use energy harvesting for storing power and need every electron they can find/store.
And every single commercial charger based on a switching power supply circuit (i.e., a LOT of them) uses capacitors on its input and output for ripple smoothing and as part of the compensation network that stabilizes the circuit's output when the load changes (transients). And also for decoupling/bypassing and charging-timeout functions too. They're not huge caps, but they are caps...and they're used in commercial chargers.
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