Page 1 of 1
Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Thu Dec 11, 2008 1:22 pm
by grovecat
When I check the voltage of the NiMH cells in my UBC73XLT after a few hours of charging, they read around 1.45V or a bit higher. That seems rather too much and I wonder if the inbuilt charger is intelligent. I sent Uniden an email about this but no response.
I'm considering having a spare set of cells and using an external charger. Is that worthwhile?
Re: Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Thu Dec 11, 2008 1:33 pm
by yorky
Sounds about right. Remember 1.2V is the lowest they should go before conking out, and normal alkaline cells start around 1.5/1.55V.
However With my portable I use an external charger for piece of mind with a spare set of cells on standby so yes its worthwhile.
Re: Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Thu Dec 11, 2008 3:19 pm
by grovecat
Thanks Yorky, I think I will get the extra cells because the ones being charged internally also got rather too hot. I know some chargers rely on a temperature rise rather than a Delta-V jump, but that has always seemed a bit primitive.
Re: Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Thu Dec 11, 2008 3:54 pm
by robbage
Yes, 1.2V is the nominal voltage for NiCd and Ni-MH. 1.4-1.5 is a good charge
Re: Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Fri Dec 12, 2008 11:07 am
by w0mbat
All this below relates just to those cells in NI-CAD or NI-MH construction.
All secondary (rechargeable)cells like AAA, AA, C and D are ~1.2V nominal.
Primary (non-rechargeable) cells are 1.5 nominal.
Secondary cells should not be charged to more than 1.25V
Secondary cells should not be discharged to lower than 1.05V
Secondary cells should never get much hotter than the ambient temp. If they do they are being over charged.
Ni-MH are exothermic so they will get warm even at C/10.
So to answer the OP question, I do not think the 73XLT has a regulated charger.
My AOR8300 doesn't regulate charging either
Re: Does Uniden UBC73XLT overcharge NiMH cells?
Posted: Fri Dec 12, 2008 4:03 pm
by robbage
Wikipedia wrote:Charging method
A NiCd battery requires a charger with a slightly different voltage charge level than a lead-acid battery, especially if the NiCd has 11 or 12 cells. In addition, the charger requires a more intelligent charge termination method if a fast charger is used. Often NiCd battery packs have a thermal cut-off inside that feeds back to the charger telling it to stop the charging once the battery has heated up and/or a voltage peaking sensing circuit. At room temperature during normal charge conditions the cell voltage increases from an initial 1.2 V to an end-point of about 1.45 V. The rate of rise increases markedly as the cell approaches full charge. The end-point voltage decreases slightly with increasing temperature.