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Topic: 4x AA Ni-Mh voltage drop on load (Read 10735 times) previous topic - next topic

polymorph

If you are measuring voltage at the input of the regulator, then that includes all the voltage drops along the way. I thought it would be unusual for a NiMH cell to drop that far in voltage.
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danielb7390

#16
Aug 14, 2014, 07:05 pm Last Edit: Aug 14, 2014, 07:25 pm by danielb7390 Reason: 1
@elac
It's better because its working  8)
There's any way to make it more efficient?

@polymorph
Before i also read the voltages on the battery pack it was same result.

If im making this right this setup should be able to run up to 2h almost? or I'm wrong?

One of the problems is the router(s) i have 2 i can use, both of them have another dc dc converter inside them! They used those linear transformers...  And yes tried direct to batteries but the voltage is low... it boots up but when connecting it drops.

elac

It's not good to drain the rechargeable batteries until the router shuts off, that will be well below the recommended discharge.
The boost module will keep boosting until there is not enough current or voltage to do so, regardless of the battery pack's state of charge.
Go with your assumption that the router will run for 2 hours and see how many cycles you get before the time your load runs becomes dramatically lower or your batteries won't charge properly.
Be aware that as the voltage of the batteries drops the modules efficiency gets worse.
For better efficiency raise the voltage of your battery pack.
2 x 9.6v battery packs in parallel a 4aH total capacity will give you around 2aH of useable current or 19.2W.
That you could safely say will run your router for 2+ hours.

As for adding another router, it might "work" for you, but with your current setup it surely will not be "properly working".
It's all about the skills

danielb7390

#18
Aug 14, 2014, 08:36 pm Last Edit: Aug 14, 2014, 08:40 pm by danielb7390 Reason: 1
You guys keep talking of battery packs problem is i cant seem to find anything for a good price!
On ebay  most of them are fake, local stores only have this batteries for digital cameras where can i get nice batteries from??

I wasn't going to run it until it shuts down, i was going for around 1v/battery 4v total pack.. isn't that the correct discharge voltage?
Also if i get more 4x AA and connect in series i should get 8x1.2 = 9.6v would that be better??

This is part of a bigger project, im converting a rc car to wifi controlled it already works perfect problem is the batteries!
The car itself used a 9.6v 900mAh battery and my friend said it would run for around 30minutes, if i bought 4 more to join like i said above would it work? I don't need huge runtime at least 30min it would be nice :)

retrolefty


You guys keep talking of battery packs problem is i cant seem to find anything for a good price!
On ebay  most of them are fake, local stores only have this batteries for digital cameras where can i get nice batteries from??


Those designed for digital cameras should work fine for servo application as both are higher current/shorter duration type loads. Any battery will have some limit of number of servos that can be manipulated simultaneously due to the specific battery's internal resistance rating.


danielb7390

The ones i got were on the digital camera section. I really didn't have much to choose from: gp or varta or sony it's the ones i saw in the stores around here...
If i can be sure that buying 4 more will solve all the problems... otherwise seems like the wifi car will get stuck... at least my LED screen is almost done  :smiley-roll:

elac

With your current setup using 800mA @ 5.12V, 2 hours of run time will be 1600mA or around 80% of your batteries total 2050mA capacity.
For only 1/2 hour of run time this is fine as you are only discharging the batteries about 20%.
But, you are pulling 40% of the batteries total 2000mA capacity to achieve this voltage boost, which is not the best for the batteries as that current has to go through the batteries internal resistance. More current = larger voltage drop = wasted power(heat) = faster wear down of the batteries.
Most 9.6v RC battery packs like the ones sold at Walmart are nothing more then 8 X AA's in series.
So a DIY 9.6V battery pack consisting of 8 x the batteries you are already using will give you around 2Ah @ 9.6V which is 19.2W total power and about 9.6W of useable power.
Your 12V 240mA load draws 2.88W of power plus the power of the boost module, whatever it is at a 9.6V source voltage.
You will be able to get around 2+ hours of run time at about a 40% discharge, but for how many recharge cycles?
More then your current setup, but also much less then the batteries rated amount of recharge cycles.
If you double the Ah capacity to 4Ah @ 9.6V and properly care for the batteries you could safely run the router for 2+ hours daily. This way you can get much closer to the batteries rated amount of recharge cycles as you would be around a 20% discharge for each 2+ hour cycle.



It's all about the skills

MarkT

When you say 4x AA NiMH pack, are these cells a pack, with spot-welded tabs,
or just 4 cells in a battery holder?

If a battery holder your problem may be the battery holder is not designed for high
current and has steel springs and rivetted contacts - these are hopeless above about
0.5A.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

danielb7390

@elac
If i need all of those just for the router don't even want to know how many i need for the rest of the rc car...
Seems like this project is going to end...  i paid 20€ for this 4 batteries ... if i need to get all of those... its way too pricey...
Don't know if makes difference, but it would be to use at worse case one a week... would that help?
Also with 8x AA router shouldn't need a external dc-dc converter since the internal one works with 7v+!
Did you take a look @ the data-sheet i placed on the 1st post?

@MarkT
Yes they are separated cells (bought with the charger).
And yes im using the battery holder but i don't see a problem there its not getting hot at all.

MarkT

The bad battery holders can drop more voltage than the cell's internal
resistance, that's the point.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

elac

#25
Aug 15, 2014, 12:59 am Last Edit: Aug 15, 2014, 04:35 pm by elac Reason: 1
Ok, let's read that data sheet where it says "Recommended discharge current 200 to 6000mA".
That being 200mA steady draw which is 10% of the 2000mA nominal capacity @ 1.3V up to 6000mA pulsed @ 1.17V.
Running the router off the internal regulator from 9.6V or 7.2V will definitely be more efficient then the 2 step process your trying to do as of now.
And it will eliminate the frequency introduced by the booster module into the RC circuitry.
Take what MarkT said about the battery holder and put together a proper pack or purchase one.
It will also prevent the batteries coming out or bad contacts when the RC is bouncing/vibrating.
It's all about the skills

danielb7390

I would love to get a battery pack problem is WHERE! Any legit ones on ebay? Amazon UK?
You guys on USA are just lucky... can buy this kind off stuff in lots of places...

elac

It's all about the skills

danielb7390

See that's no really that expensive!
Here they want 50€ just for the battery pack    =(

Are those any good? Would those work for the car and the router?

elac

Any good, I don't know never used them.
As for them "working" for the RC car + router, if the car needs 9.6v and the router will run from a 9.6v source, then yes they are the correct "working voltage". But that doesn't mean much.
Without knowing the total current draw of the combined RC car + router and how much run time is needed nobody can answer what total Ah capacity you need for your project.

Please post as much detail about your project as possible.
As it is now every answer to your questions is just raising more questions that could be avoided with more details.
It's all about the skills

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