Author Topic: Peak detection charging under load  (Read 1340 times)

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Offline rbtyingTopic starter

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Peak detection charging under load
« on: February 10, 2012, 04:55:53 PM »
Would it be possible to create an online charging system (no power loss from the load's point of view) using a NiMH battery and a peak-detection charger , more specifically the Tenergy 01005? My concern here is that the load on the battery will keep the peak detection from working, leading to an overcharged battery.

If not, what would be the best way to create such a charging system? My current method uses a relay with the NC line going to the charger and the NO line going to the load, which is suboptimal as it has a number of important electronics running from USB power. As these devices sometimes draw a significant amount of power, they can trip the polyfuse in the USB bus and thus cause problems.

Offline Soeren

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Re: Peak detection charging under load
« Reply #1 on: February 10, 2012, 05:28:22 PM »
Hi,

Would it be possible to create an online charging system (no power loss from the load's point of view) using a NiMH battery and a peak-detection charger , more specifically the Tenergy 01005? My concern here is that the load on the battery will keep the peak detection from working, leading to an overcharged battery.-
Do you by "online" mean charging with a load connected?
If so, you're right thinking that the load may fool a peak detector, but my guess would rather be too early termination, at least if the load varies/switches on-off at random times.


If not, what would be the best way to create such a charging system? My current method uses a relay with the NC line going to the charger and the NO line going to the load, which is suboptimal as it has a number of important electronics running from USB power. As these devices sometimes draw a significant amount of power, they can trip the polyfuse in the USB bus and thus cause problems.
Not qute sure what you mean by the relay setup and all, but if you want to get more current than your USB controller can supply, you could get a powered hub - or why not a separate power source?

If you want to make a charger that can charge NiMH's while under load, use temperature and terminal voltage as EoC detectors.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rbtyingTopic starter

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Re: Peak detection charging under load
« Reply #2 on: February 11, 2012, 12:01:18 AM »
Hi,

Would it be possible to create an online charging system (no power loss from the load's point of view) using a NiMH battery and a peak-detection charger , more specifically the Tenergy 01005? My concern here is that the load on the battery will keep the peak detection from working, leading to an overcharged battery.
Do you by "online" mean charging with a load connected?
If so, you're right thinking that the load may fool a peak detector, but my guess would rather be too early termination, at least if the load varies/switches on-off at random times.
Yes, I meant charging with a load connected. Do you think the charger would begin charging again if the voltage dropped to a sufficiently low level? That is, if it terminated charging because the load turned on, and then the load drained the battery, is it likely to need power cycling before it will begin charging?

If not, what would be the best way to create such a charging system? My current method uses a relay with the NC line going to the charger and the NO line going to the load, which is suboptimal as it has a number of important electronics running from USB power. As these devices sometimes draw a significant amount of power, they can trip the polyfuse in the USB bus and thus cause problems.
Not qute sure what you mean by the relay setup and all, but if you want to get more current than your USB controller can supply, you could get a powered hub - or why not a separate power source?

If you want to make a charger that can charge NiMH's while under load, use temperature and terminal voltage as EoC detectors.
I want to get more current, yes, but currently the only external power source I have is the battery that would be charging; thus, I'm looking for a way to charge it while leaving it connected to the USB hub.

With regards to making such a charger, are there any relatively simple ways to do so? I don't want to play with AC if I can avoid it, so if you know of an existing product that does EoC with dT/dt, that would be best.

Interestingly enough, my Tenergy charger does have a temperature probe, but the advertising implies that it uses peak detection instead...

Offline Soeren

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Re: Peak detection charging under load
« Reply #3 on: February 11, 2012, 07:46:12 AM »
Hi,

Yes, I meant charging with a load connected. Do you think the charger would begin charging again if the voltage dropped to a sufficiently low level? That is, if it terminated charging because the load turned on, and then the load drained the battery, is it likely to need power cycling before it will begin charging?
I don't know your specific charger so I cannot tell - but it is fairly easy to find out ;)


I want to get more current, yes, but currently the only external power source I have is the battery that would be charging; thus, I'm looking for a way to charge it while leaving it connected to the USB hub.
Why do you have a battery connected to a USB hub at all?


With regards to making such a charger, are there any relatively simple ways to do so? I don't want to play with AC if I can avoid it, so if you know of an existing product that does EoC with dT/dt, that would be best.
How many of the NiMH cells are in series?
Do you have an adapter of a suitable voltage, perhaps from some discarded piece of equipment?
If so, what voltage and current?


Interestingly enough, my Tenergy charger does have a temperature probe, but the advertising implies that it uses peak detection instead...
The temperature is used as a safeguard against the odd incidents where a semi-bad battery is too weak to give a clear dV/dT indication.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rbtyingTopic starter

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Re: Peak detection charging under load
« Reply #4 on: February 11, 2012, 10:01:42 AM »
Yes, I meant charging with a load connected. Do you think the charger would begin charging again if the voltage dropped to a sufficiently low level? That is, if it terminated charging because the load turned on, and then the load drained the battery, is it likely to need power cycling before it will begin charging?
I don't know your specific charger so I cannot tell - but it is fairly easy to find out ;)
I will test this later... it's a little time-consuming to drain 7Ah batteries.

I want to get more current, yes, but currently the only external power source I have is the battery that would be charging; thus, I'm looking for a way to charge it while leaving it connected to the USB hub.
Why do you have a battery connected to a USB hub at all?
The devices that are currently drawing too much current need to remain powered on even when the battery is charging; if I can charge the battery without removing the load, I should be able to have a separate 5v bus instead. Due to the limitations of my motor controller (a RoboClaw 2x15A), I can't communicate with it immediately after connecting the battery, and the two-second delay is difficult and unreliable to coordinate in software. My current solution has been to connect the logic power supply output of the RoboClaw to 5v from USB, thus leaving it on as long as communications are needed, but it's drawing a bit too much power once the motors themselves are enabled, dropping bus voltage down to 4.5v or so.

With regards to making such a charger, are there any relatively simple ways to do so? I don't want to play with AC if I can avoid it, so if you know of an existing product that does EoC with dT/dt, that would be best.
How many of the NiMH cells are in series?
Do you have an adapter of a suitable voltage, perhaps from some discarded piece of equipment?
If so, what voltage and current?
It's a 9 cell (10.8v) battery, so I imagine that I would be able to use a 12v/1A power adapter to charge it? Anything else I have would be too high of a voltage (laptop power supplies at 19v) or too low (9v)

Interestingly enough, my Tenergy charger does have a temperature probe, but the advertising implies that it uses peak detection instead...
The temperature is used as a safeguard against the odd incidents where a semi-bad battery is too weak to give a clear dV/dT indication.
Thanks--I didn't know that.

Offline Soeren

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Re: Peak detection charging under load
« Reply #5 on: February 12, 2012, 10:14:35 AM »
Hi,

It's a 9 cell (10.8v) battery, so I imagine that I would be able to use a 12v/1A power adapter to charge it? Anything else I have would be too high of a voltage (laptop power supplies at 19v) or too low (9v)
NiMH cells need to be charged to 1.40V to 1.45V (charge termination voltage), so a 9 cell battery needs to be charged to 12.6V-13.05V and you need at least half a volt over that from the charger.

You could use a booster circuit to use either the 9V or the 12V supply, but if it's OK to use your laptop charger, it wouldn't be hard to make a current limited constant voltage (taper charger) circuit for that.

What is the capacity rating of your battery?

You should still use the dV/dT charger for charging every now and then (perhaps once a week or once a month) to keep the battery in mint condition.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rbtyingTopic starter

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Re: Peak detection charging under load
« Reply #6 on: February 12, 2012, 11:28:37 AM »
NiMH cells need to be charged to 1.40V to 1.45V (charge termination voltage), so a 9 cell battery needs to be charged to 12.6V-13.05V and you need at least half a volt over that from the charger.

You could use a booster circuit to use either the 9V or the 12V supply, but if it's OK to use your laptop charger, it wouldn't be hard to make a current limited constant voltage (taper charger) circuit for that.

What is the capacity rating of your battery?

You should still use the dV/dT charger for charging every now and then (perhaps once a week or once a month) to keep the battery in mint condition.

Ah, I see. I do have a spare laptop charger, which I believe is rated at 19v. The capacity of the battery is listed at 5Ah, and I have another one which is listed at 7Ah.

Do you have any resources/schematics on how to make a taper charger? If so, that would be extremely helpful.

Thanks

Offline Soeren

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Re: Peak detection charging under load
« Reply #7 on: February 12, 2012, 12:22:41 PM »
Hi,

Do you have any resources/schematics on how to make a taper charger? If so, that would be extremely helpful.
I can draw you one, but what is the battery capacity (in Ah or mAh)?


Edit: On further thoughts, if used only as a help for keeping the batteries from draining while working on the program or whatever, the 12V supply should be fine on its own, if it can deliver approximately the equivalent of the average drain (or more). This will keep the battery at 1.33V/cell.
« Last Edit: February 12, 2012, 12:37:56 PM by Soeren »
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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