electronicsuk
Newbie level 4
nimh float charge
Hi all. I have an application where I need to construct a DC power supply with battery backup. My initial intention was to use lead acid cells for the backup, but there is very limited space available inside the enclosure the circuit will be mounted in which rules this out. Instead I'm leaning towards a pack of high capacity NiMh AA cells, they offer the benefit of a much better capacity to physical size ratio.
My question is, is it possible to charge NiMh cells with a constant low current in the same way as you would float charge a lead acid? Again, due to size limitations I need to keep the charging section as simple as possible, preferably just a case of a single current limit that will be suitable for both initially charging the cells from flat and providing a standby charge current to overcome the cells self discharge rate.
I'm worried that after a year or so this form of charging might cause some damage to the battery, and wondered if anyone had any thoughts on the issue? Would it be reasonable to expect a good service life from this sort of arrangement, and what would be a good charge rate to choose? Again, I'd prefer as little active circuitry as possible but if different bulk charge and float currents are the only way then I could design them in.
Thanks in advance
Matthew
Hi all. I have an application where I need to construct a DC power supply with battery backup. My initial intention was to use lead acid cells for the backup, but there is very limited space available inside the enclosure the circuit will be mounted in which rules this out. Instead I'm leaning towards a pack of high capacity NiMh AA cells, they offer the benefit of a much better capacity to physical size ratio.
My question is, is it possible to charge NiMh cells with a constant low current in the same way as you would float charge a lead acid? Again, due to size limitations I need to keep the charging section as simple as possible, preferably just a case of a single current limit that will be suitable for both initially charging the cells from flat and providing a standby charge current to overcome the cells self discharge rate.
I'm worried that after a year or so this form of charging might cause some damage to the battery, and wondered if anyone had any thoughts on the issue? Would it be reasonable to expect a good service life from this sort of arrangement, and what would be a good charge rate to choose? Again, I'd prefer as little active circuitry as possible but if different bulk charge and float currents are the only way then I could design them in.
Thanks in advance
Matthew