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Aplication Examples-cycling transmitter NiMH batteries
Usually I start with discharging to reach some reference status. Graupner Tx doesn’t allow higher discharging than 1.5Amps (perhaps due to PCB and provided charging cable). For NiCd and NiMH I treat batteries depleted if voltage is around 0.9V per cell. For my Tx 8cell pack it’s 0.9*8=7.3V, this will be terminating voltage. I can prolong discharging using 0.3A parameter i.e. even if discharged pack will reach 7.3V, I will continue discharging until pack will give 0.3A (sure 7.3V limit won’t be exceeded). I found it’s not necessary and with such bad pack maybe not recommended. One should be milder to not 100% status packs. I guess limit 1.0-0.8Amps should be enough and will serve for our purpose, also discharging will be shorter. |
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| On picture above you see discharging graph. You can see also small Voltage drop-out (1), it's about 0.1V (XY zoomed, switched to measurement mode and using User Calculation mode). No idea why it's here, but as I said this pack is not in the best condition. Anyhow, after 3 months there was still 0.8Ah capacity. Pack is discharged.
Now I will charge it (using page C). This is Tx pack, therefore no high C currents are recommended. Generally slower is better, but Im not so patient. Especially if its NiMH, Panasonic and not 100% pack (internal resistance is very high and AUTO mode of charger will take very long time). I start with 0.8Amps, I don’t wan't preliminary stops of charging. I will setup 16V limit (it’s 16/8=2.0V percell) as security measure. DCPM algorithm will work for me here therefore if you setup 49V, doesn’t matter. 3000mAh (0.8*4=3.2Ah) should be charged within 4hours with reserve. You can setup safety limit 320min and also 3.2Ah. |
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| Above you see charging graph. At the end of charging there is again some slight drop-out (aprox.0.1V). This pack was long time not cycled, therefore maybe these drop-outs. When I cycled battery later on, these drop-outs dissapeared. Anyhow we reached capacity nearly 3Ah, that's good.
Bellow you can see overlay of discharging cycles. First "rest" discharging is (1). In second discharging (2) you can see again voltage drop out. In third discharging cycle this drop out is already missing (3). Also voltage graph is a bit more flat (that's good). You should also note discharged capacity at 1.5A is only about 2.6Ah. Hmmm, I said this pack is nothing extra... |
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| Bellow you can see overlay of charging cycles. First charging (1) was performed in MAN. mode (NiMH2, 0.8A). In second charging (2) I used AUTO mode. I used NiMH2 which is a bit more rapid than NiMH1. NiMH1 is basically considered for cells with higher internal resistance and NiMH2 is for hard, low resistance cells. Sure my Tx cell should be charged perhaps with NiMH1, but I'm unpatient , therefore NiMH2. You can see that automat selected lower current (0.5A). Charging took much longer time, but when you look at picture above, discharging overlays, discharged capacity was the same i.e. in this case has lower charging current no efect. In third charging cycle (3) I used again MAN. mode. BTW drop out at delta peak is already missing. Pack is getting slowly reconditioned. | |||
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| OK, you can see that we can use both AUTO and MAN. NiMH programs to successfuly charge even "bad" pack with high resistance affected cells. In this case I usually prefer MAN. mode, while AUTO is conservative and takes longer time, but it's your choice. Condition for this procedure is that I know exactly what type of cell I'm going to cycle. Always use security features like limited voltage (aprox 1.6V/per cell in charging NiCd, NiMH) and limited capacity (add 10-15% of nominal pack capacity). | |||
Well, let’s start with first example. It’s the end of February and my transmitter (Tx) Graupner MC-24 is long time stocked in my Alu case under the table. It wasn’t used nearly 3-4 months. My Tx is equipped with 8 cell old NiMH Panasonic 3000mAh (no idea about exact product number). These batteries were nothing extra when they were brand new and now they are even worse, but when checked on PowerCube I can be quite sure they are working, still.
