Advise on powerfull battery power supply & cha

Forum 2005-2010 (read only) Hardware Interfacing
1

I am going to update my wifitank to a better platform


Dimensions (mm): 200x170x105

but the battery from my old is a 9.6V ni-cd from a drill, which is close to perfect, because it is a good voltage for both the motors and the arduino, it can power the entire thing for 3-4 hours with more or less constant use, plus it can be recharged in about 20 minutes with the original charger, but the problem is the weight and size of it.

To get the battery on the platform, it will be at the very end to make room for the servo that will hold the camera, and make it very unevenly balanced.

I am now trying to find something that will be about as powerful, but smaller.

Only thing I can think of here is li-po, but only thing I know about those is that they need the right right charger, otherwise they could become dangerous.

I have tried the lipo rider form seeedstudio, and it is quite nice, but only charges with max 500mA and can only output 5V and 350mA

The 5V would be usable for the arduino, but it is only just enough to make the motors turn, and with the 350mA it would then probably drop to something that wouldn't make them run.

Maybe I could use multiple lipo riders to bring the current up, but it would still charge the batteries very slowly.

Anyone got any ideas on what I could use?

Total sensors and so on the tank is
2 servo motors
4 proximity sensors
2 ping sensors
4 motors for the wheels
~8 leds for night driving
1 seeeduino mega
1 wishield 2.0
1 h-bridge motordriver
1 wireless camera (around 200ma)

I haven't tested how much current the new platform will draw (still waiting for it to arrive), but the old one I used was pulling around 2A while starting both motors at the same time, then around 500mA with both of them continuous spinning afterwards

2

I would suggest LiPO batteries, parallel up as many as needed for the current draw you want, and use a switching boost regulator to get the voltages you want efficiently.
Example,

this is really just 3 1100mAH batteries in series, use this to power the motors,
and this (or European supplied equivalent)

to make 5V, 600mA for the 5V parts.

What you don't want to is pump high voltage thru a little heat generating 7805 to make a lot of current at 5V, that's just wasting run-time power.

Or you can come up with other combinations to suit your needs, such as stay with 3.7V as the source, and boost it to 12V, 20V, etc whatever the [edit] batteries motors need, and a 2nd to make 5V for the arduino & other logic.
Say a discrete battery for each motor with its own boost regulator, and a 3rd for the arduino/other logic. No magic formulas, find a combo you can live with.

Maxim-ic.com makes a bunch of battery charger control chips, you could look into making your own, some require less components than other.
http://para.maxim-ic.com/en/results.mvp?fam=batt_chrg
For example, I have a max1811 in a remote control to charge a 3.7V 1000mAH LiPO battery, only needed a couple of caps and a resister, and an optional R & LED to show when it was charging since I do not monitor it with a uC.

3

I totally third LiPo's. They're wonderful batteries, so long as you're nice to them.

You could also put cells in series instead of using a boost converter. Switching power supplies, especially ones sourcing a lot of current can be noisy (electrically) and a bit more work to put together.

4

Lipo batteries do have the best energy density and are available in all sorts of voltage and current capacity. The hardest thing is to find a proper charger for multicell lipos as it's possible over time for the individual cells in a series connected pack to become unbalanced and damage can then result for individuals cells being overcharged or over discharged compared to the other cells in the pack. There are chargers avalible that are able via extra connectors to track individual cells in a series pack and rebalance the pack as it charges them, sometimes called balancing chargers. Most of the IC chip based chargers are only useful for single cell, 4.2vdc applications where balancing of multicell packs isn't an issue.

Proper operation of lipo batteries is essential as there is a real fire danger from overcharging, short circuiting and over discharging a lipo will also destroy it. You should research the subject carefully if you are new to lipo batteries. They are quite the state of the art in battery tech but do have critical parameters to understand and obey.

5

Sounds like li-po would be great for what I need, but the risk might be too high...

The wifitank is going to be drivable as before, but I want to make a charging stand for it, so it can drive into it and be recharged.

With the charger I got right now it isn't a problem, because it got 3 connections, gnd, plus, temperature, and if one of them isn't right, it simply won't charge. And it takes very little to make it stop charging again and blink with an error.

So when it can be driven into the charger by people, and later hopefully be able to find the charger it self, it also need to be something that can charge without anyone watching it. (will add a smoke detector to it, and something to cut the main supply to the charger if it goes off)

The battery I am using right now also got short circuit protection in, so it cuts off if something happens, then first starts again 30 seconds after the short circuit has been removed.

6

GRRRR!!!

Just took my old battery apart to see if it was possible to relocate the cells inside it... And here is what I found...

7

So you have some corrosion looks like, some soldering, some of those spot-welded kind of leads that are impossible to get undone...

I tried to replace the batteries in a cordless drill battery pack. Couldn't find a way to attach leads to the c-cell size batteries in it. New battery pack costs as much as a new drill with new higher voltage batteries.

8

This is quite easily to solder on, so I might be able to cut the metal between the cells, and replace it with some thick grounding wire instead. That way it might be small enough to be on the low level of the robot chassis.

I just don't hope the corrosion will do too much damage, would be irritating to modify it, if it dies very soon.

The reason that I want to stick to this is mainly the charger. It is very fast (charging from 6V on the battery, back up to almost 12V in 20 minutes) to fully charge it, and the tank can then run for hours again afterwards, and at the same time it will be very easy to make the arduino on the tank look at the charger, and see what it is doing (led on while charging, blinking slow when done, blinking fast on error)

9

Isn't the corrosion a sign that some battery leaked & needs replacing?

10

Probably, but the hours of use was only like a week ago, this doesn't look that fresh... Think I will try, and use it till it gets too bad

11

You could also use NiCad batteries. They can source a lot of current and be charged quickly and you can treat them fairly poorly without them exploding (like over charge them indefinitely if you do it slow enough). Of course there is the whole memory issue so you have to be willing to replace them relatively often.

12

I think that is what I already got, the label says Ni-Cd

13

Gell Cell lead acid ?. Decades old technology, they ironed all the creases out long ago......... Cheap if heavy and will stand a degree of abuse (a shed load of abuse compared with LIPO) . Charging circuit is cheap and simple, doesn't terminally die if the voltage drops too much, can produce huge currents in the short term (If you want to melt screwdriver shafts with battery power, this is the way to go).

http://www.batterymasters.co.uk/Product-Powersonic-ps630,-6V-3.0-Ah-Lead-Acid-Rechargeable-battery_1149.aspx

14

I'd suggest some Ultrafire 18650's. I use them and they're generally the same batterys in laptop packs and drill batterys.

15

hehe, getting more and more confused about what to go with...

First choice will probably be the current battery, even when it is showing signs about dying... But at least it should be able to keep me going for some time and read more about the options.

And as CrossRoads mentioned in the first reply, the step-down regulator would be better than the 7805's, I think I will still go with two 7805's for the servo motors, but connect a TIP102 so they aren't powered when the servo's aren't needed. (would switch the power to the servo motors off anyways)

How easy would it be to make a charger for the Ultrafire 18650's if I went with those?

I would probably use 3 or 4 of them in series to get 11,1V or 14,8V, and maybe then two of those sets in parallel to get more amps (servo motors, plus 4 wheel motors at the same time)

Gell Cell lead acid ?. Decades old technology, they ironed all the creases out long ago......... Cheap if heavy and will stand a degree of abuse (a shed load of abuse compared with LIPO) . Charging circuit is cheap and simple, doesn't terminally die if the voltage drops too much, can produce huge currents in the short term (If you want to melt screwdriver shafts with battery power, this is the way to go).

Also a good suggestion, but they also seems to be very big (and as most people, I want them small with same power as a nuclear reactor, and I want them for free... :P)

The good thing is that the charger seems to be very simple to connect the the battery, and the price on both battery and charger is pretty low.

Another plus is that the battery is a easy shape to make a mount for, and eventually stack things around it, without having an odd shaped battery (like the round ones that require the right holder)

My summary so far...

Li-Po
Sounds like they do exactly what I want, but the price on both charger and battery is a bit high for my budget, plus the risk of charging the batteries wrong is too high (unattended charging)

NiCad
Seems to be able to do the job, but the 'memory issue' will be a big problem, as it would be able to drive into the charger without being fully discharged, and then 'destroy' the battery way too fast.

Li-Ion
Could maybe be used, but the voltage and maybe the need for a custom charger might make it difficult.

Sealed Lead-Acid
Seems to be both at the right price, the right voltage, and have a fairly simple charger. Only thing is that they might be a bit big, but at the same time also having a shape that makes them easily modular with the rest of the thing.

16

Have you thought about 9.6V NiMH packs for R/C cars? They are cheap, and available nearly everywhere...

17

Have you thought about 9.6V NiMH packs for R/C cars? They are cheap, and available nearly everywhere...

Yes, have thought of them, but years ago (like 8-10), a friend had one of his battery packs exploding/rapidly-melting while in use. Haven't liked them since, but don't know if anything about them is changed since.

I can get a 3A charger and a 4000mAh battery here for 100$ (plus 15$ shipping, hurray for ridiculous high shipping inside the country)

18

Yes, have thought of them, but years ago (like 8-10), a friend had one of his battery packs exploding/rapidly-melting while in use. Haven't liked them since, but don't know if anything about them is changed since.

This can happen with any battery due to abuse and/or age (abuse would be defined as drawing maximum current for a period of time - so you see this happen often in R/C racing conditions, as well as battle robotics - though it is considered "normal", which is why you have backup packs).

I remember as a kid witnessing a small AA alkaline battery explode on my bookshelf (due to age); sounded like a firecracker, and launched the positive end across the room...

This is thing about batteries; we all want them small with the power of a nuclear reactor with little cost - but if that were true (LiPo's come closest, so far), they would be very dangerous with improper usage, storage, and charging (just like we see with LiPo's).

19

I can get a 3A charger and a 4000mAh battery here for 100$ (plus 15$ shipping, hurray for ridiculous high shipping inside the country)

I would actually want to see the charge/discharge rates for the cells used in that pack before I would put a 3A charger on a 4AH pack; that seems like a supposed "quick charger", and it seems like an overly high rate. It likely works, but you probably don't get as many charge/discharge cycles out of a pack before it fails (either in the car or on the charger). This isn't a real issue while racing or otherwise, but it could be interesting for experimentation.

I would look into getting a slower charger (even if it takes more hours to charge), and buying a few packs to rotate around on the charger. That, or invest in a "fireproof" charging cage of some sort (or constantly monitor the charging)...

20

So the "battle" must be between Sealed Lead-Acid and the NiMH packs...

But isn't the NiMH more for rapid use, and the lead-acid for over time?

Because it is going to be mostly idle, waiting for someone to control the vehicle around, only powering the camera (might connect that through a tip102 too to switch it off while not in use)
But when it is controlled, it probably draws between 1 and 2A, and maybe with some very short spikes higher than that

I would look into getting a slower charger

It got two settings, 1.5A or 3A