Rechargeable Battery Pack Mod

[Hopey]

Hiya. I'm thinking of doing a mod to make a rechargeable version of the standard battery pack. I've got 3 of these already and several of the next few sets I'm planning on getting include one as well, so no huge loss if I muck it up.

The plan is to get a 9.6V battery pack something like this and put them inside it. By eyeball measuring it, I think there's enough room to fit 8 AA batteries in at right angles to the standard way. I'd solder these up in series and attach them to whatever terminals the standard 6 battery connectors use. This would give 8x1.2V = 9.6V, which should be safe to use with the 9V kit.

Once inside, it'd be permanent, so I wouldn't have to make it so that they can be changed; I can just ram them in and hot-glue the lot in place. I might need to do a bit of hacking bits out with a dremel so that the outside looks nice.

I've seen instructions for a mod to use a 9.6V battery pack as it, but it requires cutting an extension cable and adding an extra switch, and leaves you with a big ugly battery pack. Since I'd be using the original circuitry, I wouln't need to wire in any extra switches or anything, and the entire thing would externally still look like the standard battery pack, and could be incorporated into models in the same way.

A couple of questions though:

• Has anyone pulled on of these apart? I had a quick go at removing the two screws, and it seems that the part that holds the batteries should slide out, but it didn't seem to want to come apart and I didn't want to destroy it just yet. Is it possible to get it apart without destroying the circuit board?
  
• How would I go about charging it? I'd incorporate a nice discrete socket to plug something into for charging. Do I need a special charging device, or can I just use any old spare DC transformer I've got lying around? What kind of voltage/amperage would I need?
  
• Performance wise, how would this compare to 6 good alkaline or 6 rechargeable batteries?
  
• What kind of batteries do I want? NiMH? LiPo? Something else?
  

Cheers!

[locoworks]

rechargeable batteries have a lower voltage than dry cells. nicads typically 1.2 volts, nimh slightly less. you could just put nicads instead of dry cells in the battery box but fully charged you would be just over 7 volts instead of 9. your 8 cell pack idea i assume is to get full voltage in the box, but it could be enough power with 6 cells to be useable though not with the same oomph?. if there are no resisters or anything in the box you should be able to recharge the box by converting a lego block to plug onto the outlet. i'd unplug everything from the battery box before i recharged it though because the dirty charge current may upset any electronics wired to it. alternatively if you want 8 cells and cant get AA's to fit you could use AAA's and have shorter run times, or even forget the battery box altogether if the superstructure can withstand its loss and just replace it with an 8 cell pack??

[le60head]

Great idea! Looking forward to results.

About the disassembly of the standard ( AA-type) PF Battery box:

After you remove the two side screws, it's fairy easy to pull out the center part, which contains the battery beds.

Good luck with the project!

[hrontos]

• How would I go about charging it? I'd incorporate a nice discrete socket to plug something into for charging. Do I need a special charging device, or can I just use any old spare DC transformer I've got lying around? What kind of voltage/amperage would I need?
  
• Performance wise, how would this compare to 6 good alkaline or 6 rechargeable batteries?
  
• What kind of batteries do I want? NiMH? LiPo? Something else?
  

Cheers!

I think, it should be possible to charge them using the existing connector on the battery box.

Just cut one brick connector from the PF extension cable and replace it with proper connector for the charger.

Final solution will look nicer than any connector added to battery box.

As a charger for 8 batteries shops for RC car or plane fans offer chargers able to charge 8 AA batteries, since the same setup is used in RC remote controlers. Such charger takes care of the batteries properly, is able to sense the voltage and properly selects charging current according to state of the batteries. Price of these chargers is comparable to price of 8 NiMH AA rechargeable batteries. May be it is better to use standard AA rechargeable batteries, because you can select your preffered brand and capacity.

From performance point of view, rechageable batteries can provide more current than alkaline and since you compensate lower voltage by using 8 instead of 6, it should be really nice battery box.

I do not recommend LiPo batteries. They are better, but their charging is more complicated and it is easy to make them explode when charged improperly.

[DLuders]

On his website, Philo wrote this topic about the Lego Power Functions Battery Box, complete with picture instructions on how to access the inside:

[Hopey]

Thanks for the tips. Might be a little while before I get the funds together for a charger.

As for using regular batteries, I think that constructing something with contacts such that I can easily pull them out is a bit beyond me, and I've never had much success trying to solder wires onto the ends of batteries. Might be worth a shot though.

[Nazgarot]

If you can afford to spend some money on it you could invest in Li-Ion batteries in AA size. They have about 3,6 Volts fully charged, and if you modify the wiring of the box to put 2 series of 3 batteries in parallel you would have (3,6*3=) 10,8 Volt and (2*2400=) 4800 mAh. That should make for a very powerful battery!

I've been planing to do the same for a while, but haven't gotten around to buying the cells yet. (got a son the 9. of may, and that requires a lot of time...) :)

Please remember to get batteries that can deliver enough continuous current. The example I linked to can't, but there are batteries that can... And be careful how you recharges these. They need a Li-Ion compatible charger and can't be quick charged.

-ED-

EDIT: corrected a spelling mistake.

Edited July 19, 2012 by Nazgarot

[Lighti]

If you can afford to spend some money on it you could invest in Li-Ion batteries in AA size. They have about 3,6 Volts fully charged, and if you modify the wiring of the box to put 2 series of 3 batteries in parallel you would have (3,6*3=) 10,8 Volt and (2*2400=) 4800 mAh. That should make for a very powerful battery!

I've been planing to do the same for a while, but haven't gotten around to buying the cells yet. (got a son the 9. of may, and that requires a lot of time...) :)

Please remember to get batteries that can deliver enough continuous current. The example I linked to can't, but there are batteries that can... And be careful how you recharges these. They need a Li-Ion compatible charger and can't be quick charged.

-ED-

EDIT: corrected a spelling mistake.

I would suggest using sanyo eneloops... (there are rebuilds from other companies with the same technique meanwhile, for example ansmann maxE) they are able to hold the voltage and current quite well over nearly the full "load".

This is usually a problem of high mAh NiMH Batteries, they have by design for example 2800 mAh and 1.2V voltage, but after like the 1400 they drop below 1.1V which results in less power.

And the eneloops hold their power over quite a long time (if I recall right, 80% over 1 year) so they sell them precharged. So you wouldn't have to recharge them everytime before usage if you just played a little bit 1 month ago.

[Nazgarot]

I would suggest using sanyo eneloops... (there are rebuilds from other companies with the same technique meanwhile, for example ansmann maxE) they are able to hold the voltage and current quite well over nearly the full "load".

This is usually a problem of high mAh NiMH Batteries, they have by design for example 2800 mAh and 1.2V voltage, but after like the 1400 they drop below 1.1V which results in less power.

And the eneloops hold their power over quite a long time (if I recall right, 80% over 1 year) so they sell them precharged. So you wouldn't have to recharge them everytime before usage if you just played a little bit 1 month ago.

I'm currently using those, and they can deliver a lot of current, and doesn't fall below 1.5 Volt as fast as normal NiMH batteries. They do how ever slowly crawl towards 1.1 Volt, and will not pack as much of a punch as alkaline batteries in PF (they can have voltages as high as 1.7 when new).

The main problem with PF is how ever not to deliver current, or keep a charge over time. It's that the PF elements has over current protection. The only way to make PF more powerful is by using a higher Voltages. That is why I've been considering the Li-ion batteries.

But, I would still recommend trying the eneloop batteries as they are quite practical.

-ED-

[jacobkristensen]

On his website, Philo wrote this topic about the Lego Power Functions Battery Box, complete with picture instructions on how to access the inside:

Speaking of Philo, I am looking forward to the time when i he get around around to study the new PF-SV motor. I don't know if has just gotten a crawler(9398) or if has got the PF-L motor from somewhere else.

[Hopey]

So I've done the first prototype, with mixed success.

Even though I'm using old, not-too-fancy batteries (they've been in and out of Wii remotes for 3 years or so), there's a significant improvement in power. My pseudo-crawler has much more torque available now, and can actually crawl over some things. It's so much better that the steering now clicks and destroys itself when it reaches lock. So that aspect's a goer.

As far as fitting within the battery pack and looking as pretty as the original, well, lets just say my eyeball measurements were a bit optimistic.

The batteries stick out about another 1 stud length out the bottom. So besides looking hideous, it probably won't fit inside a model. There's also nothing stopping the batteries from falling out at the moment, and I don't really have any ideas other than duct tape.

That's the battery assembly. As you can see, I butchered the insert that normally holds the batteries, keeping just enough to mount the connector and PCB, which needs to be in just the right place for the switch to work. This is actually the main problem, as it takes up more space than I'd anticipated, and is what leads to the batteries sticking out the bottom.

The actual assembly of the battery series was quite simple. I didn't want to modify the batteries at all, as this is just a proof of concept; if it works I'll buy some dedicated batteries (probably eneloops) and put these ones back in the Wii remotes. So the series was achieved by placing a bent paperclip across each junction in such a way that it wraps around the positive terminal and contacts the next negative, and holding it in place with the tape. Then a looped one at each end to attach the wires to, and a bunch more tape around the outside to hold it all in place. This works better than I'd expected; they don't seem to lose contact at all, however, if/when I do it permanently, I'll figure out a way to solder wires onto the terminals.

The PCB assembly only takes up one side of the top of the thing, which should leave me enough space to add a small charging socket next to one of the screws.

The outer part needed some modification as well. There's two ridges on each side which the inner insert slides along. These made the space just slightly too narrow to fit the batteries in, so they needed to go. If I had a dremel or the patience to do it with a stanley knife, I'd have used that, but I went for a soldering iron instead. The trimming down of the insert was done with this as well. Not pretty and one must be very careful. I melted one of the edges where the covers slot in. Oops.

So I'm not sure what the next step is. I'm very pleased with how it performs, but the aesthetics clearly need a lot of work.

How much charge do AAAs hold compared to AAs?

Besides using AAAs, any suggestions on how to make it go together?

[edited - typos]

Edited July 20, 2012 by Hopey

[Costas]

Rechargeable AAA's typical have less than half the capacity of their AA cousins.

For instance - AA Eneloops are rated around 2000mAh capacity whereas the AAA variants are around 700mA.

The other thing to point out is that the 'Internal Resistance' of the AAA sized cells is worse than the AA sized ones.

This basically means that the AAA cells will drop their voltage more under the same load. So if you have two packs [one AA and one AAA] that consist of the same cell count [eg: 6 cells = 7.2v] then the AA sized pack will give you better performance [faster running motor(s) etc] for the same load.

Edited July 21, 2012 by Costas

[gti180]

try two bat packs and 4 batteries in each and charge across them both

[Hopey]

*Bump*

So I've had another go at this, using AAA batteries this time. Obviously this means it won't hold as much charge, but it all fits inside now, and looks much prettier.

Not going to do a full instructable, but basically, I hacked out the baffles that normall go between the AA batteries, to make space. I also made a bunch of 'notches' in various places where I needed wires to run through. I did this by melting it with a soldering iron and cleaning it up with a craft knife. A dremel or similar would be better, but I don't have one.

I connected up the batteries in two groups of 4. I soldered them together this time. I wasn't sure if I could get a good join, but by scratching the battery surface on the negative end, and making a little wire lassoo to go around the positive end (and scratching it too) I managed to get the solder to grip quite well.

The two 4-packs were connected in series, with a wire going around the outside, and ran the end wires to the places where the existing wires attach. I also added an additional wire to each for charging it. The soldering of these two connections is pretty bad; I should've cleaned the soldering iron after melting all that plastic. It'll do.

These are just molex connectors from an old broken PC power supply, since they fit in the plug that's already on the charger I found. So currently, I can just pop the cover off and attach these wires when I want to charge it, and they tuck away neatly in the left over space when I'm not. In future I might get around to making a nice charging socket with a 3.5mm plug or something.

So that all works. Both covers go on, and there's no externally visible difference, hence the blue pin for me to differentiate it. Not much point posting a photo of that.

Now I just need to see what the battery life is like...

[z3_2drive]

I've had this custom rechargable battery that my father made for a while now! It uses 3 very powerful lithium batteries which create 10-11V, and it's connected to the pf receiver so theres a regulator on it so it doesnt burn the receiver. sadly no case so it's a bit tough finding a place to put it on my models, especially because of the triangular shape. I charge it by putting on alligator clips onto the contacts, hooked up to a power supply box. It lasts very long. A bit dangerous but saves lots of batteries I have two and nearly lost one when one of my rc cars lost signal and plunged into my pool, but I grabbed it so only the front half and motors got wet. everything was ok.

Edited July 29, 2012 by z3_2drive

[Hopey]

It uses 3 very powerful lithium batteries which create 10-11V, and it's connected to the pf receiver so theres a regulator on it so it doesnt burn the receiver.

Could you tell me more about this regulator? I considered putting 10 AAA batteries in for 12V (which I think would have fit, with some effort), but read that although the motors would be fine with this, it'd probably damage the IR receivers.

Edited July 29, 2012 by Hopey

[z3_2drive]

Could you tell me more about this regulator? I considered putting 10 AAA batteries in for 12V (which I think would have fit, with some effort), but read that although the motors would be fine with this, it'd probably damage the IR receivers.

Yes, we tried without regulator, and burned out our receiver . We fixed it and now use regulator. google the part# '78L09' Good luck!

Edited July 30, 2012 by z3_2drive

[Hopey]

Did you use the regulator part I told you about in your other topic, since I see the custom batteries.

Nope, just using the two battery packs from above. Both are only 9.6V; version 1 is 8xAA, version 2 is 8xAAA. I did a bit of reading, and it seemed as though installing a regulator would just absorb any extra current, so with a 9V regulator I'd get no real advantage from having 10 batteries at 12V over 8 batteries at 9.6V. I may be wrong in my understanding though.

Is there any way in which 10 batteries giving 12 V via a 9V regulator would be better than 8 batteries giving 9.6V with no regulator?

[Traktor]

Nope, just using the two battery packs from above. Both are only 9.6V; version 1 is 8xAA, version 2 is 8xAAA. I did a bit of reading, and it seemed as though installing a regulator would just absorb any extra current, so with a 9V regulator I'd get no real advantage from having 10 batteries at 12V over 8 batteries at 9.6V. I may be wrong in my understanding though.

Is there any way in which 10 batteries giving 12 V via a 9V regulator would be better than 8 batteries giving 9.6V with no regulator?

I guess you would be able to keep the "output" voltage above 9v for a longer time with the 10 batteries setup, if that is not eaten up by the regulator.

[Hopey]

Bumpety bump.

I've now got two of these, each with 8 very cheap rechargeable AAAs in series (I re-did the AA one with AAAs)

I just put one of them on to charge for a few hours, after which I switched it on, and the light on it didn't come on.

So to begin troubleshooting, I measured the voltage across the two charging wires, which connect directly to either end of the battery series. 0V would mean that one of the inter-battery connections has come undone, ~9.6V would mean that something was up in the circuitry, switch, or connection from the batteries to the circuit.

But I got 0.3V.

Does this mean I've cooked one or more of my super-cheap batteries, and I should have been less cheap and bought some eneloops?

[Moz]

But I got 0.3V.

Does this mean I've cooked one or more of my super-cheap batteries, and I should have been less cheap and bought some eneloops?

I suspect you have at least one cell that is almost-but-not-quite open circuit. Remember that the resistance of the multimeter is very, very high, so you can almost measure static electricity. I'd open the pack up and measure each cell. If you have a decent charger you could split the pack and cycle each cell to see whether they're any use at all.

But the real answer is yes, you should have bought decent cells in the first place. For this you really do want the tabs. Soldering to button cells is difficult and likely to damage the cells, the the resistance of the spring contacts is so high you are probably better off soldering. When I measured for another project I was getting ~0.3 ohms per cell from a 4 cell holder with bridged cells in it. Putting al-foil in the contacts helps, but is very fiddly and tedious.

Looks as though solder tabbed Eneloops are available, and one of the (rumored) suppliers is just round the corner from me so I will contact them and see what they say. For merkins it seems to be easy, but then this forum is mostly merkins so they may just have looked at local importers: http://www.candlepow...abbed-Eneloops� There is a Dutch supplier in the list, so: http://eu.nkon.nl/sa...ldeerlipje.html

Edited January 6, 2013 by Moz

[Moz]

Got a response from Master Instruments who passed me to BatteryDoctor. They say:

We just tag the cells in our workshop as requested. http://www.batterydo...&product_id=764

$1/cell for tagging The basic HR-3UTGA is $4 ea so $5.00 ea tagged. Tags are 4.7mm x 22mm.

I think I will order 8 and see how I go. Looks as though the new higher capacity Eneloop XX is only available in AA at this stage though. And, of course, since they're well made the cells last for many cycles and the ones I bought 5 years ago are still going strong...

Edited January 7, 2013 by Moz

[legoman666]

I have a locomotive that uses 4 L motors which are powered by 2 IR receivers in parallel which are then powered by 2 AA battery packs that are filled with Eneloops. I was unhappy with the top speed provided by only 7.2V. I just finished (Literally, 15 minutes ago) attaching 1 of these to each of the AA battery packs: http://www.ebay.com/...984.m1439.l2649

They are after the battery packs but before the IR receivers. I set the output to 10V and my train zips right along now :D No more droop when the batteries aren't full. I have all of the electronics (except the motors) in a 7 stud wide autorack car that's 48 studs long.

I also had to bypass the resettable fuse in the AA battery packs; I kept tripping it at high speed. Working great.

FWIW, I'm an electrical engineer.

Edit, lol, just noticed this was from 2013, not 2014. Oh well.

Edited January 22, 2014 by legoman666

[ddimkin]

Hi legoman666, if I use same setup es yours on a 9398 Crawler with battery mod:

http://www.ebay.co.uk/itm/Led-Lamp-6400Mah-18650-8-4v-battery-Pack-for-xml-T6-P7-LED-lamp-/251001613660?pt=UK_SportsLeisure_Camping_LightsLanternsTorches&hash=item3a70dcad5c

with the same regulator set to 10v output will it work? The crawler has 2 x L-motors and 1 x servo. Even if it works fine I am afraid that the servo motor might start braking/disassembling the car as written by someone else on the forum.. can't find the topic.

Thanks a lot!!