Battery Charger Design
in [Design]
|
From: thorin92 on 5 Jan 2010 07:34 Dear group, I am trying to design a battery charger for this battery: http://uk.farnell.com/varta/55615605940/battery-pcb-mount-6v-5-v150h/dp/863981 I'm familiar with voltage regulators and current limiting etc. but am unsure what parameters to use? If I simply provide 6v limited to 70mA will this work? Thanks in advance
From: mike on 5 Jan 2010 08:12 thorin92 wrote: > Dear group, > > I am trying to design a battery charger for this battery: > > http://uk.farnell.com/varta/55615605940/battery-pcb-mount-6v-5-v150h/dp/863981 > > I'm familiar with voltage regulators and current limiting etc. but am > unsure what parameters to use? > > If I simply provide 6v limited to 70mA will this work? NO unless you comply EXACTLY with the conditions of that number in the spec. Not likely. > > Thanks in advance To design a battery charger, you have to disclose a LOT about how the battery is used. Simplest thing is to charge it at 4.2ma. Spec at the link says it will last 6-years being abused like that. But that may not meet your cycle requirements, that you haven't stated.
From: MK on 5 Jan 2010 08:16 "thorin92" <thorin92(a)gmail.com> wrote in message news:36597a80-dd0f-4e96-a16b-ceda719358de(a)u41g2000yqe.googlegroups.com... > Dear group, > > I am trying to design a battery charger for this battery: > > http://uk.farnell.com/varta/55615605940/battery-pcb-mount-6v-5-v150h/dp/863981 > > I'm familiar with voltage regulators and current limiting etc. but am > unsure what parameters to use? > > If I simply provide 6v limited to 70mA will this work? > > Thanks in advance There is a lot more to charging batteries than that ! 70mA is the fast charge max current and you must not charge continuously at that level. Varta recomend voltage controlled charge. Look at www.linear.com and find the LTC4060 data sheet - this may not be suitable for your application but it will give you some ideas. The Varta data on the Farnell web site is very sparse - look at some other battery data and apps notes to find out more. Michael Kellett
From: thorin92 on 5 Jan 2010 08:18 On Jan 5, 1:12 pm, mike <spam...(a)go.com> wrote: > thorin92 wrote: > > Dear group, > > > I am trying to design a battery charger for this battery: > > >http://uk.farnell.com/varta/55615605940/battery-pcb-mount-6v-5-v150h/... > > > I'm familiar with voltage regulators and current limiting etc. but am > > unsure what parameters to use? > > > If I simply provide 6v limited to 70mA will this work? > > NO unless you comply EXACTLY with the conditions of that number in the > spec. Not likely. > > > Thanks in advance > > To design a battery charger, you have to disclose a LOT about > how the battery is used. Simplest thing is to charge it at 4.2ma. > Spec at the link says it will last 6-years being abused like that. > But that may not meet your cycle requirements, that you haven't stated. Hi Mike, thanks for the reply. The battery will be discharged at around 50mA over 3 hours, then re- charged as fast as possible. Its for a portable device running a load of LEDs (like a bike light) A long life needs to be maintained because the battery will be permanently attached to the pcb. Does that inspire any more help? Cheers :)
From: mike on 5 Jan 2010 08:49
thorin92 wrote: > On Jan 5, 1:12 pm, mike <spam...(a)go.com> wrote: >> thorin92 wrote: >>> Dear group, >>> I am trying to design a battery charger for this battery: >>> http://uk.farnell.com/varta/55615605940/battery-pcb-mount-6v-5-v150h/... >>> I'm familiar with voltage regulators and current limiting etc. but am >>> unsure what parameters to use? >>> If I simply provide 6v limited to 70mA will this work? >> NO unless you comply EXACTLY with the conditions of that number in the >> spec. Not likely. >> >>> Thanks in advance >> To design a battery charger, you have to disclose a LOT about >> how the battery is used. Simplest thing is to charge it at 4.2ma. >> Spec at the link says it will last 6-years being abused like that. >> But that may not meet your cycle requirements, that you haven't stated. > > Hi Mike, thanks for the reply. > > The battery will be discharged at around 50mA over 3 hours, then re- > charged as fast as possible. Its for a portable device running a load > of LEDs (like a bike light) > > A long life needs to be maintained because the battery will be > permanently attached to the pcb. > > Does that inspire any more help? Cheers :) Often, the most difficult part of a project is writing the spec. Words like "as fast as possible" will get you loads of input that may be VERY bad tradeoffs. Still insufficient information, but... Unless you have some SERIOUS size/weight constraints, your battery is probably too small. What's your definition of "discharged"? If you mean voltage cutoff at a level that guarantees none of the 5 internal cells gets reversed, you have a chance of success. If you mean run it 'till the light goes dim, your battery will NOT have long life. Charging is problematic. Depending on the NUMBER associated with "as fast as possible", you may have no option but to use a smart battery charger chip. I'm assuming this is a production device that requires agency approvals and you care about customer retention. If it's an advertising giveaway device, put lithium coin cells in it and ship it. Replaceable AAA-cells that the customer has to recharge externally will save you a LOT of grief. Customers cuss the internal battery when the light goes dim at midnight when they're half-way home. |