Introduction: Hoover Tiffany (5240) Robot Vac Lithium Battery Upgrade

Picture of Hoover Tiffany (5240) Robot Vac Lithium Battery Upgrade

In this instructable I am going to show you how to convert your (dead?) Hoover 5240 model vacuum cleaner into a lithium powered monster. This is my first instructable, I have spent a number of years browsing others ideas and helpful hints, and now it's my turn to return the favor.

A few years ago, Hoover created an inexpensive, attractive compact robot vacuum series known as "Tiffany", "Miranda" and "Levi". They have great colours and we were often found talking to Tiffany as she was working around the house. She became a member of our family. Unfortunately, Hoover decided to power the 5240 range with NiMH battery technology, and these cells have are notorious for losing capacity in a short period of time. Tiffany worked for about 20 months before failing to store charge in her battery pack, so I decided to upgrade her to the more modern lithium technology.

I can see that a lot of these great little units will probably be sitting in the trash, or second hand stores because of the failed battery, you could even try and get a bargain one at a garage sale!!! Don't forget to lookout for some laptop battery pack to strip too ;)

Items you will need:

  • #8 Torx screwdriver
  • Sharpie or other marker pen
  • Soldering iron & solder
  • 20 gauge coloured wires
  • Electrical / Insulation tape
  • Side cutters
  • 4x 18650 lithium ion batteries (salvaged from an old laptop)
  • 4cell Battery Management System (BMS) (ebay - AU$2.75)
  • Multimeter
  • Optional but very helpful, "Helping Hands" clamps.

Step 1: Step 1: Disassembly of the Original Battery.

Picture of Step 1: Disassembly of the Original Battery.
  1. Firstly, turn off your 5240 vacuum cleaner. The little switch on the right hand side is what we are after.
  2. Next, turn the vacuum onto its back and squeeze in the little black clips around the battery, whilst applying some pulling force to remove your pack. This might be a bit tight, especially if the cells have swollen with their demise.
  3. Using your #8 Torx driver, remove the 4 silver screws and carefully remove the battery case lid.
  4. Place the screws and the black retention tabs and tab-springs onto the lid and set safely aside.
  5. Using your Sharpie/Marker pen, mark the positive and negative positions on the case for later. There is a white lead on the other side, up to you if you mark that or not.
  6. Carefully remove the positive connector tab, and wrap it with a little bit of insulation tape.
  7. Repeat step 6 for the black negative, and white thermistor leads.
  8. Cut the leads as CLOSE to the battery pack as you can, and place them aside with your case.
  9. You will notice another larger thermal fuse wedged between the cells, you can leave that if you want. I didn't bother using it.
  10. Wrap exposed terminals of the old NiMH pack with electrical tape and set aside for recycling.

Step 2: Step 2: Preparing the 18650 Batteries.

Picture of Step 2: Preparing the 18650 Batteries.

!! DISCLAIMER !!

Lithium batteries can be explosive. Be very careful not to short circuit or damage them in any way. This includes heating with solder. Try not to spend more than 4 seconds with your iron on the end caps.

  1. Mark the positive and negative ends of the batteries with your pen.
  2. I like to scratch up the ends of the terminals before soldering, it really helps the solder to bind to the nickel. I just use the pointy end of my side cutters, but if you have a exacto knife and are not prone to cutting yourself feel free to do it that way :)
  3. Crank your soldering iron up to it's maximum heat, and apply a blob of solder to one end of each battery. I stand them on end, and do the positive end (+) first. This lets them cool again before proceeding with the negative (-) end. Also, placing the battery inside your electrical tape tube will stop it from rolling or falling over.
  4. Using some electrical tape, loop it back on itself to create "Double sided tape" and stick your Battery Management System (BMS) to a battery.

Step 3: Step 3: Pack Construction.

Picture of Step 3: Pack Construction.

Take a quick look at the Battery Management System (BMS) diagram. Basically, you solder all the batteries in series. Each cell, taps onto the board so that the BMS can monitor the state of every lithium cell during charge and discharge.

  1. With that image in mind, take a piece of 20AWG wire, and solder it to your first battery's + end.
  2. Trim the wire to length, tin the end and solder it to the first point on the BMS (B+)
  3. Cut 3 pieces, 25mm length of 20AWG, I used yellow, to be the interconnects between the cells.
  4. Solder one of the 25mm interconnects to a different colour for the 2nd cell of our pack. (orange)
  5. Stand both batteries in your electrical tape to make your life easier when soldering to the 2nd battery's + terminal
  6. Straighten the batteries so they are now inline, tape them for stability, then check the length of orange cable needed to reach the "B2" pad on the BMS. Strip and tin, then attach to the BMS.
  7. Take another 25mm interconnect and solder it to another colour wire (blue).
  8. Solder the interconnect to the negative (-) terminal of your work in progress
  9. Solder the other end of the interconnect and blue lead to the positive (+) of your new cell.
  10. Cut your blue wire to reach the BMS "B3" pad, strip and tin with solder and attach to the BMS.
  11. Tape your work down, for tidiness and stabiltiy.
  12. Take your last interconnect and solder it to another colour wire (grey).
  13. Solder the interconnect to your work in progress negative (-) end, and to the new cells positive (+) terminal.
  14. Once again, take another colour wire (black), solder it to your negative end (-) cut it to length and attach it to the final pad on your BMS named "B4".

The basic pack is now built.
You can test the battery voltages on each of the pads using your multimeter. Start on B+ with your red lead of the multimeter. Put the black lead on the B2 tab. It should read anywhere from 3.3V to 4.2v, depending on the state of charge (SoC) of your batteries when you salvaged them. To measure the next battery, put the multimeter red lead on B2, and the multimeter black lead on B3.... ad so on. To check the overall output of the pack, put your multimeter red lead on P+ and the black lead of the multimeter on P-. My pack measured 15.6V.

Step 4: Step 4: Final Battery Configuration.

Picture of Step 4: Final Battery Configuration.

Be careful with this next step, as a short circuit can really ruin your day with a lithium cell. Explosions are not uncommon.

  1. Take the white lead with the thermistor, solder the exposed end to your packs negative (-) end, then tape the thermistor to the closest cell.

  2. Take the original leads from Step 1(8) and solder the black lead to P- on your BMS.

  3. Solder the red lead to P+ on your BMS.
  4. Carefully insert the battery pack into the original case, taking care NOT to short circuit any of the exposed connectors
  5. Take the BLACK lead, and place the metal clip/terminal into the case where you marked the (-) from disassembly. But if you didn't do that, it's in the closest position to the cells. Press down to ensure it's in firmly. Press the cables down to ensure they don't get pinched or cut during assembly.

  6. Take the RED lead, and place the metal clip into the case where you marked the (+) from disassembly.

  7. Take the WHITE lead and place it in the final spot.

  8. Check all wires are routed smoothly, and cannot pinch when you put the case back together.

  9. Insert the springs and black clips to the battery box, then put the lid on. Ensure you have it around the right way :) and carefully close. Insert the screws and tighten. You are done.

  10. Test the voltage across the terminals with your multimeter. You should get from 13V to 16V depending on the charge.

  11. If all good, insert the battery case back in your "Tiffany", turn her over and flick the power button to "ON". Hit the "Spot Clean" and let her clean up the mess you just made on the floor with the wire stripping :)

  12. Once she is done there, put her back on the charger. It will take a long time to charge, and if you are paranoid like myself, check every 30 minutes or so with your multimeter to make sure nothing is going mental.

Now, those keen image spotters may notice that I doubled the cell count in my Tiffany, you don't have to. I have effectively used 2 BMS circuits to create a 4s2p (4 series, 2 parallel) pack. It keeps the voltage at 16V, but doubles the mAH count. Tiffany can run for about 3 hours with her new pack.

Comments

KegRaider (author)2017-05-02

I can report back to anyone interested, that this pack is still working great. I still have the original 8 cells, with the two "el cheapo" ebay BMS modules. Tiffany runs around everyday from 7:30AM until almost 11AM. She is exactly the same as she always was, in terms of noise and erratic behavior, but has a lot more stamina! Approx 3.5Hours of runtime. Take note Mr Hoover, install Lithium cells in your robot vac, they're much better.

I'm guessing they used brushed motors in her as well, and that will be the next thing to replace :)

mrygula (author)2017-03-03

I've tried this on a roomba a few years ago, but it did not work well. After about 5 minutes it would turn off and beep that it needed charging, even though the batteries were still all at 4 or so volts per cell. Maybe it had something to do with the crappy cells I bought from ebay.

KegRaider (author)mrygula2017-03-04

Hi Mrygula,

The Roomba may have been trying to draw more current than your cells could provide. You may have had one bad LiIon cell, that's what happens with laptop packs, one cell effectively kills the lot. Do you recall if they were hot? Did you use thick enough gauge wire? The 20AWG wire should be good for 11Amps, which is way more than I require.

Also, what voltage requirement is the Roomba? Did you match it or get close enough to the original design?

Swansong (author)2017-03-01

I'm glad you could fix it! :)

Jeff22 (author)Swansong2017-03-01

Hi, Nice Project! Did you use the battery charger from the nimh battery pack to charge the new pack you Made? Thanks

KegRaider (author)Jeff222017-03-02

Hi Jeff22,

The ebay BMS manages the charge state of the batteries. The internals of the Hoover delivers charging power to the battery pack at about 17V, and the BMS takes over from there. I may revisit the solution if I find that the cells are failing or *gasp* exploding, but in the few weeks it's been operating, all has been fine.

The only issue I have noticed since installing is, the "Full Go" option doesn't function, as it doesn't actually get full in it's eyes. A full NiMH pack will "Burp" to let it know it's done 14.4V. The LiION pack should not get overcharged due to it's higher voltage capacity of 16.8V. The most I have seen the pack charge to is 16.1V, which is well below the maximum of the lithium cells.