ION/ IRON

Real Classic - - Letters -

With re­gard to Gra­ham Lamp­kin’s ‘Charge Query’in RC152 on the sub­ject of lithium iron or lithium-ion bat­ter­ies, you need to dis­tin­guish the two chem­i­cal types, as op­er­a­tion and charg­ing con­di­tions can be quite dif­fer­ent. There are sev­eral use­ful ref­er­ences on­line: ‘Be care­ful about group­ing all lithium bat­ter­ies into one group, there are ac­tu­ally many dif­fer­ent chem­istry mixes in­volved. Tra­di­tional Li-Ion bat­ter­ies are a no-no for re­plac­ing lead-acid in mo­tor­cy­cles. The ones avail­able on the mar­ket for this ap­pli­ca­tion are LiFePO4 – Lithium Iron Phos­phate. This is a very sta­ble con­fig­u­ra­tion and very tol­er­ant of abuse that would cause a Li-Ion bat­tery to ex­plode. Main ben­e­fits are weight-sav­ings since they weigh only 20% of what a lead-acid would for the same ca­pac­ity. And take up about 50% as much space.’

The crit­i­cal fac­tors, as when charg­ing any type of bat­tery, are the charge volt­age, charge rate or cur­rent and charge du­ra­tion. If you charge a bat­tery at too high a rate, it will get hot and if there is no way to vent the gases pro­duced by charg­ing, this will re­sult in an ex­plo­sion. Sim­i­larly, bat­ter­ies will get hot if charged for too long, so it is im­por­tant also to limit the length of the charg­ing pe­riod.

The best ad­vice is to do some re­search and read the fo­rums be­fore you buy. Ox­ford Prod­ucts pro­duce a charger for lithium iron phos­phate bat­ter­ies.

From what I read, it is im­por­tant to re­strict the charge rate for these bat­ter­ies, both in or­der to avoid dam­ag­ing the charger and to re­strict the volt­age in or­der to avoid dam­ag­ing the bat­tery. It ap­pears that lithium iron phos­phate bat­ter­ies also need to be charged at a slightly higher volt­age than lead-acid bat­ter­ies. John Black­burn, mem­ber 11,656

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