0
\$\begingroup\$

The diagram is from a wall mounted vacuum cleaner.Photo's of the system and the new batteries

What can the green thing be and what could its price be so i can replace it?

Can i use 7 x AA NiMh batteries with 4800mAh each at 1.2 V ?

Can i redo the system so it works with the aformentioned new batteries and doesn't overcharge or be set on fire?Diagram of the vacuum cleaner

\$\endgroup\$
6
  • 1
    \$\begingroup\$ This seems to be a duplicate of your previous question. \$\endgroup\$ – Transistor Feb 2 at 21:59
  • \$\begingroup\$ it is, i ll delete the 1st one since it didnt have the schematic or some info. Now everything i got is up there... \$\endgroup\$ – Alexis Stavrianidis Feb 2 at 22:00
  • 3
    \$\begingroup\$ OK, but the right way is to update the original question. It won't make much difference in this case as there are no answers yet. \$\endgroup\$ – Transistor Feb 2 at 22:02
  • 2
    \$\begingroup\$ The green thing is a resistor, but I don't think you'll be able to measure its value now. \$\endgroup\$ – user_1818839 Feb 2 at 22:24
  • 1
    \$\begingroup\$ @AlexisStavrianidis - Just FYI, regarding: "AA NiMh batteries with 4800mAh" - there is no such thing. The ones like your photo are fake. The maximum real AA NiMH capacity is currently around 2850 mAh, they cost quite a bit, and are less suitable for high current loads (like a vacuum cleaner motor) than some lower capacity batteries. Notice that the original cells were 1500 mAh. See this page which shows examples of some fake AA NiMH battery capacities. \$\endgroup\$ – SamGibson Feb 2 at 23:25
0
\$\begingroup\$

That resistor controls the charge current to the batteries.

You can't measure or read that resistor anymore, so we must do a little sleuthing to figure out what it should be.

NiMH batteries do not like overcharging, and if that's impossible to prevent (it is in your case), then you should do only a trickle charge of about 0.05C

https://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

You should charge the batteries at (1500mA) * (0.05) = 75mA (max)

You have 11V from the adaptor, dead batteries will be around 1.2V, so that resistor needs to drop (11V - (7 * 1.2) ) = 11 - 8.4 = 2.6V

To limit charge current under 75mA, the resistor needs to be:

2.6V / 0.075 = 35 ohms or more

47 ohm is an easily obtained standard value. Picture looks like a 1/2W device

https://www.ebay.com/itm/47-Ohm-0-5W-1-2-Watt-5-CF-Resistors-Qty-5-Bonus/223631630544?hash=item34117be0d0:g:FQQAAOSwoOddXWHo

BTW, I don't expect you to follow the calculations or the justifications unless you want to ;) I put them there so the community can keep me honest.

BTW BTW, are you sure you have SEVEN (7) batteries in that green wrap? Looks like SIX (6) to me. 7 would be a very unusual configuration.

\$\endgroup\$
3
  • 1
    \$\begingroup\$ it says on the wrapper 8.4V that's seven cells. \$\endgroup\$ – Jasen Feb 3 at 1:25
  • \$\begingroup\$ Can you tell me at which point i have to place the resistor, on the diagram i posted? \$\endgroup\$ – Alexis Stavrianidis Feb 4 at 0:59
  • \$\begingroup\$ I dont understand why its imposible to create a new system to protect it from overcharging, isnt there a way to have fluctuating currect over time or something? I can find the charger made for the new batteries if it helps, although i think the numbers will be for 4 batteries.. Thanks for the reply! \$\endgroup\$ – Alexis Stavrianidis Feb 4 at 1:11
0
\$\begingroup\$

I have the same vacuum cleaner and I changed the batteries with 6x18650 2850mah three in a series two in parallel it gives us a total of 11.1 (12,6 full charge) volts 5700mah I removed the resistor and bridged it with a wire, I put a bms for the batteries protection and I changed the power supply to a larger 12.6 volts. the motor has no problem with the higher voltage the vacuum cleaner works even better than before.

\$\endgroup\$
4
  • \$\begingroup\$ Note that charging LiIon without a charger designed for them will at best undercharge them and probably shorten their lifetime or destroy them. Floating 3S LiIon at 12.6V is a very bad idea. \$\endgroup\$ – Russell McMahon Mar 21 at 1:35
  • \$\begingroup\$ thank you for the note i have put a battery indicator to see how much it has charged also than throwing the vacuum in the trash I chose to put 18650 because if I put the same they might not have the expected duration I'm not electronic I just know some things so I would like to hear your opinion on future projects for something safer. thanks! \$\endgroup\$ – kostas tsg Mar 21 at 18:39
  • \$\begingroup\$ Their are many chargers available specifically designed for LiIon charging. You CAN make your own but it is cheaper to buy one. A minimalist charger will charge to N x 4.2V and then REMOVE voltage immediately. A usual charger then holds the voltage at N x 4.2V and removes voltage when Icharge reduces to some fraction of Ichgmax - 50% is usually a good choice. | Leaving Vchg connected is a bad idea. \$\endgroup\$ – Russell McMahon Mar 22 at 11:44
  • \$\begingroup\$ Thank you! I will buy a charger then specifically for this \$\endgroup\$ – kostas tsg Mar 25 at 18:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.