Help needed with replacement of burnt out transistor

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Discussion Overview

The discussion revolves around the replacement of a burnt-out resistor in a hair clipper that uses rechargeable Ni-Cd batteries. Participants explore the implications of replacing batteries with different capacities and the necessary resistor value for proper charging.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the appropriate resistor for a pair of 850mAh rechargeable batteries after a previous resistor burnt out.
  • Another participant seeks clarification on whether the issue involves a transistor or a resistor and questions the type of batteries used, noting that NiMH and NiCd batteries have different charging requirements.
  • A participant corrects the initial post, confirming the batteries are Ni-Cd and providing the correct capacity of the old batteries as 600mAh.
  • One participant suggests that the new batteries may have a lower internal resistance and discusses the implications of the clippers' unregulated charging circuitry, recommending a starting point for the resistor value based on typical charging currents for Ni-Cd batteries.
  • A participant expresses uncertainty about identifying resistor types and requests guidance on what resistor to purchase before acquiring a job lot from eBay.
  • Another participant advises on determining the resistor value based on the charger's output voltage and the configuration of the batteries, emphasizing the need to consider power dissipation in the resistor.
  • A participant provides details about the charger’s output voltage and speculates that the batteries are connected in parallel based on their identical connections.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact resistor value needed, and there are multiple viewpoints regarding the implications of the battery types and charging configurations. The discussion remains unresolved with various suggestions and considerations presented.

Contextual Notes

There are limitations regarding the assumptions made about the charger's characteristics and the internal resistance of the batteries, which could affect the calculations for the resistor value. The discussion also highlights the potential risks of further damage without precise knowledge of the charging circuit.

hornet1blue
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does anyone happen to know what resistor i would need for
a pair of 850Mah rechargeable batteries as the one in
my hair clipper burnt out when i replaced the old
rechargeables which were 300Mah cheers
 
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Clarification, please. Your title mentions a transistor, but your OP asks for a resistor; which is it? Also, are these batteries NiMH or NiCd and did you replace the old ones with new ones of the same type? The two are NOT interchangeable because the charging requirements are different.
 
whoops sorry title should be resisitor. The batteries are Ni-Cd Uniross the old ones are Sanyo Nikel Cadmium 600Mah not 300 as I thought before. (same as Ni-Cd i think!?)
 
Tough to say. It sounds as though the new batteries have a lower internal resistance than the old ones. Unfortunately your clippers have cheap charging circuitry which uses an unregulated voltage source with a series resistor to produce a current source for the charging the batteries. Typical slow charge currents for charging NiCds are generally designed to met C/10 levels ( C being the rated capacity). For 600 mAH cells, you therefore want to aim for 600/10 or 60 mA charging current. You may need to experiment a bit to determine the optimum resistor value (don't forget about power rating!) but a safe place to start would be about double the value of the old resistors.
 
im rather new at recognising resistor types especially the burnt out one, I really need to know what resistor i should replace with. I am buying a job lot of resistors from ebay but would like some rough idea before seeing if they can cope!?
 
Can you make out any of the color bands on it? If not, you need to know what voltage the charging circuit is applying to it and whether the batteries are being charged in series or parallel. A safe assumption is to consider the battery as having zero internal resistance and the resistor will therefore need to be (V[charger] - V[battery]) / .060. This will necessarily result in a high value for R, but you can adjust it down from there. Remember, once you have your value for R, you need to plug it into the power equation ( P = I^2 * R) to determine how much power it will be dissipating so you can size it properly.

NB: Note that without knowing the precise characteristics of the charger there is some risk of further damage here, so you have to decide if it's worth it or not.
 
the charger puts out 5-6V Max 5watts input is 100-240V 50-60Hz 0.2amps. Without any real reference I think the batteries are being charged parallel as they are identically connected at both the positive and negative ends
 

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