replacing ni-cd batteries question

Thread Starter

klein

Joined Feb 27, 2010
10
hi
My spouse has an elec broom that needs batteries and all i can find are ni-cd 1.2v 1600mah and the ones that came with it are ni-cd 1.2v 1700mah, is there any reason the 1600mah shouldn't work and charge ok ?
 

cork_ie

Joined Oct 8, 2011
428
NiMH would also do the job and are likely to have more power for their size and have the added bonus of not having the NiCad "memory effect"
 

crutschow

Joined Mar 14, 2008
24,309
NiMH would also do the job and are likely to have more power for their size and have the added bonus of not having the NiCad "memory effect"
But be aware that NiMH may have different slightly different charge characteristics then a NiCad and may be less tolerant of trickle charge current.
 

Thread Starter

klein

Joined Feb 27, 2010
10
so i can replace the ni-cd 1.2v 1700mah with NiMH 1.2v 1700mah and not have to change the fuse or the charging system at all ?
 

bountyhunter

Joined Sep 7, 2009
2,512
so i can replace the ni-cd 1.2v 1700mah with NiMH 1.2v 1700mah and not have to change the fuse or the charging system at all ?
Probably not correct: NI-MH will not tolerate the sustained charge current most chargers send into the Ni-CDs. It will kill them over time.

When we worked with Gates, their rule was the sustained charge current for NI-MH should not exceed c/40. Most Ni-Cds easily tolerate sustained charge of C/5.
 

cork_ie

Joined Oct 8, 2011
428
Check what type of charger you have. Most modern home chargers are suitable for either type.

It really makes very little difference during the charge phase, both types should be charged at approx 10% A/h rate for 10 hours .
Some NiCad chargers continue with a smaller trickle charge long after the battery is fully charged. These would not be ideal for NiMh.

There is a world of info here http://www.buchmann.ca/chap4-page1.asp
 

Thread Starter

klein

Joined Feb 27, 2010
10
thank you all

but until i'm more comfortable with the charging system of the broom quick and dirty fix is to just use the ni-cd batteries.

although in the future changing it to NI-MH, i'm going to check into.

the charging board is three diodes one resistor and an led and an 12v wall-wart plugs into 110v and then into the broom.

i'm going to draw out the circuit maybe i will understand it more.
 

bountyhunter

Joined Sep 7, 2009
2,512
thank you all

but until i'm more comfortable with the charging system of the broom quick and dirty fix is to just use the ni-cd batteries.

although in the future changing it to NI-MH, i'm going to check into.

the charging board is three diodes one resistor and an led and an 12v wall-wart plugs into 110v and then into the broom.

i'm going to draw out the circuit maybe i will understand it more.
I guarantee that type has a lot of continuous charge current. Not for NI-MH.
 
NiCads are really good at dumping huge amounts of current. It's just an electric broom, probably not worth too much investment. Just about anyone can order them for you, but it will still involve soldering them in. If we leave out the fact that it is impossible to get one of those things to last, soldering the battery tabs is the "really tough part." You may imagine it to be easy, but without designing and building a spot welder attachment, making a high current connection to nickle with a soldering iron is never really right.


From a tec stand point, ones one of the series batteries fails, one of the others will be reversed charged during the alliance's use. (With my De Walt that problem costs more for a replacement battery than most entire tools do.) One of the series batteries failing is statistically impossible to avoid, and when the manufactures instructions don't tell you how to charge it, most consumer battery devices usually fail due to being left plugged in. Once one of the battery's "remember" that it is never completely drained, at least one of the others cell will be certain to fail during the next use of the device. (My landlords', brand new weed-eater is currently plugged in and charging, in it's hanging bracket on the wall behind me, as it has been for the past 3 months. I should use it, twice, and while the warranty is still good.)


It may be "solvable" for space satellites, but for the practical money making tool, I haven't yet thought of anything better than buying a cheap power tool battery at a lumber yard and useing those cells
 

crutschow

Joined Mar 14, 2008
24,309
...........................

the charging board is three diodes one resistor and an led and an 12v wall-wart plugs into 110v and then into the broom.

i'm going to draw out the circuit maybe i will understand it more.
If that's all the circuitry the charger has then it apparently just charges the batteries with a continuous charge current and doesn't drop to a trickle charge after the batteries are charged. NiCds can tolerate that (with reduced life) but NiMH cells generally can't.
 

Austin Clark

Joined Dec 28, 2011
412
If that's all the circuitry the charger has then it apparently just charges the batteries with a continuous charge current and doesn't drop to a trickle charge after the batteries are charged. NiCds can tolerate that (with reduced life) but NiMH cells generally can't.
Could you please explain your reasoning behind thinking it's using a constant current source? What are you thinking the circuit looks like?
 

Thread Starter

klein

Joined Feb 27, 2010
10
ok i got the batteries, hum i ordered the wrong ones i was more intent on getting the same 1600mah than the correct size of the battery.
so i needed c's and i ordered sc's (sub c's) will they still work in moms broom.
 

Audioguru

Joined Dec 20, 2007
11,251
When we worked with Gates, their rule was the sustained charge current for NI-MH should not exceed c/40. Most Ni-Cds easily tolerate sustained charge of C/5.
Energizer and a Japanese Ni-MH battery manufacturer also recommend that a trickle charge should not exceed C/40.

Appliances powered from old Ni-Cad cells blast them with a very high trickle current.
 

Audioguru

Joined Dec 20, 2007
11,251
When we worked with Gates, their rule was the sustained charge current for NI-MH should not exceed c/40. Most Ni-Cds easily tolerate sustained charge of C/5.
Energizer (American) and a Japanese Ni-MH battery manufacturer also recommend that a trickle charge should not exceed C/40.

Appliances powered from old Ni-Cad cells blast them with a very high trickle current.
 

crutschow

Joined Mar 14, 2008
24,309
ok i got the batteries, hum i ordered the wrong ones i was more intent on getting the same 1600mah than the correct size of the battery.
so i needed c's and i ordered sc's (sub c's) will they still work in moms broom.
If the batteries have the same Ah capacity and they will fit, then they should work.
 

crutschow

Joined Mar 14, 2008
24,309
Could you please explain your reasoning behind thinking it's using a constant current source? What are you thinking the circuit looks like?
With such few parts, all it can have is a rectifier to convert the AC to DC and a resistor to determine the (fixed) charge rate. There apparently is no circuitry to reduce the charge rate after the battery is charged.
 
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