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>> Home > Tags > nimh

nimh
nimh
Fairey Huntsman & Swordsman by jarvo Fleet Admiral!   Posted: 11 days ago
Hi Andy, I have 'twined both the 34" and the 48" Huntsman, i used 600 size motors in the 34, and 850 motors in the 48. Both were very quick, but, the run time was poor, about 10 mins. With modern lipo's or big Nimh batteries they would be a lot longer especially if you used brushless motors. Props, on the 34, they were 35mm x 3 blade brass, on the 48, they were 45mm x 3 blade brass. Sad but i sold them some years ago but now have a 48" fireboat to play with. Mark

Happy Hunter by jarvo Fleet Admiral!   Posted: 13 days ago
No worries mate, have the esc's got a max and min voltage??? they may not work at 6volts, if not then a set of 7.2v NimH packs will be brilliant x2 or possibly 4 packs with a Y lead for each pair, 3300mah packs are going for a good price on ebay at the moment, also have a look at component shop and hobbyking, be sure you are on the uk site to keep the postage down!!!! Wouldn't bother with lipo batteries, SLA or NimH are more user friendly. If you want the H/H superstructure try contacting Krick they now make the kit, took over from Robbe when the went bust. Are the propshafts ok??? withdraw the shafts and lightly oil them get the oil into the inner bearing as well. Mark

NimH advice by alex54 Seaman   Posted: 14 days ago
Hi Dave, Thanks for the pointers, I'll definitely give it a go, you explained the construction of the pack very well!

NimH advice by Dave M Fleet Admiral!   Posted: 14 days ago
Hi Alex They will be connected in series with the positive connected to the negative. I suggest you carefully cut off the heat shrink covering, taking care not to cut into the cells. You can then check each cells voltage. The nominal is 1.2v rising to 1.4v when charged. Any around 1v or less will never hold a charge so mark them with a marker pen. Hopefully it will be one of the end cells that has failed. On your type of pack the bottom of the battery (negative) will be in a metal case attached to the top (positive) of the next cell. I use a flat blade screwdriver to separate the cells (they are spot welded) and sometimes you can get the case off the bottom of the dud cell, leaving it attached to the positive of the next cell. I suggest you then charge the remaining good cells to see if they all take a full charge. If they are OK you can get a new cell or just make a lower voltage pack. I use a piece of stranded wire to repair the joint. You will need a 40+watt iron and some solder paste, and may need to scratch the battery case and pin for the solder to take. If you were careful with removing the heat shrink you can use it to cover the pack with a bit of electrical tape to make good. Please ask if you need any guidance with the process. I have been doing this for many years and may not have explained in enough detail if it's new to you. Do remember if the battery is charged it can short in its unwrapped state so do make sure you bench is uncluttered and kept clear of any metal objects. Good luck

NimH advice by alex54 Seaman   Posted: 14 days ago
Hi Dave, It would be great to salvage something from it so I would be happy to get the soldering iron out. The pack is the stick type with all the cells end to end, do you know how these would be connected together? Thanks, Alex

NimH advice by Dave M Fleet Admiral!   Posted: 14 days ago
Hi Alex Yes sounds like one cell has gone. You can probably feel the heat from the faulty cell after charging and discharging. If you are competent you could split the pack and identify the failed cell. A meter across each cell whilst running a small motor will show up any low voltage cells. Chances are the rest will be ok and will take and deliver a full charge. If so and you can use a soldering iron and can purchase replacement cells of the same make and capacity you could make the pack OK. I'd even consider rescuing all the good cells and making a lower voltage battery, 5 amp batteries being the price they are.

NimH advice by alex54 Seaman   Posted: 14 days ago
Thanks guys. I've tried cycling it twice now and it's only delivering about 3000mAH instead of the 5000mAH spec so I think I will need to replace it.

NimH advice by Dave M Fleet Admiral!   Posted: 17 days ago
You could try cycling them both. NiMhs do lose charge, as Havelock, over time but a few discharge / charge cycles can sometimes restore them. I usually charge and discharge cells I have not used for some time before recharging prior to a sailing session.

NimH advice by Haverlock Fleet Admiral!   Posted: 17 days ago
Probably NiMh batteries "self discharge" so will over time drop towards zero. If you are not using them you should keep charging them regularly so their chemistry remains good.

NimH advice by alex54 Seaman   Posted: 17 days ago
I have two 10 cell NimH stacks I bought about three years ago that I've left laying around on the bench since first charging them. Just charged them again and one has reached 14V and the other only 12.5V. Is the lower voltage one shot? Thanks, Alex

46" Firefloat What Motor/Battery by jarvo Fleet Admiral!   Posted: 22 days ago
Hi J. Your motors are nominal voltage 7.2v. Try a single 7.2v 3300 NimH pack, quality from Component Shop. It will be short running time, powering 2 motors but will give you an idea of performance, then you could buy a second, 1 for each motor, if this did not work out or you want more performance then go for brushless motors, still with the 2 battery packs. I would try the single pack first, suck it and see, develop it from there without breaking the bank!!!! Cant see any ESC, have you got 1 or 2? if 1 use a 'Y' lead to connect the second battery. Mark

46" Firefloat What Motor/Battery by jarvo Fleet Admiral!   Posted: 22 days ago
HI JJ. Your question about a safety bag, Damaged / overcharged lipo's can catch fire, think of the Boeing scandal that grounded the fleet last year. Charging in a safety bag is advised the bag is fire retardant material, which will contain any problem. Your remarks about the boat not coming onto the plane is down to the weight of the battery, my fireboat started with 7.2v NimH packs 1 for each motor, Graupner 700bb's, good cruise but not quick, but short run time, 10mins. I have re-wired to allow 3s lipo's, but not had chance to test it yet, but should go like stink. With a fast hull, weight is important, 4 x lipo packs, 1kg, half the weight and possibly 6 times the power delivery. In your first post you mention 600 motors on 6volts, they are probably rated at 8.4volts, same as my 700's hence the lack of performance, also the battery, at 12ah it should last about 30mins, was it fully charged??? and is it showing at least 6volts, ie not got a duff cell??? Canabus, in his post described an ideal set up with brushless motors, 1600 watts is just over 2 hp, 750 per horsepower so you can see the difference in performance with different motors and battery set up's

Sea Queen Prop shaft by Dave M Fleet Admiral!   Posted: 23 days ago
Hi AndyG Not sure what type of coupling was supplied but I use a common Universal coupling on my 48" Sea Queen and use a brushless 42 size 850Kv water cooled motor of 700 watts and it is happy driving a Prop Shop prop of 42mm at 45 amp on full throttle. Power is from an 11.1v Lipo of at least 2200 mA but Nimhs would work, just not as fast and less duration. My motor is mounted in the main cabin and I have no problem with the prop shaft. Originally designed for IC power so perhaps you have heard of problems when we used such powerful and not so well controlled devices. My model goes on the plane very easily and any more power would make it unstable. Pics attached to show my set up. You can just see the coupling in front of the motor.

Voltage step down by jarvo Fleet Admiral!   Posted: 24 days ago
Hi Brian, I would suggest 2 x 6volt NimH cell packs with a parallel 'Y' lead, the reason is you can use each pack to alter the trim of the hull. with a big hull like the Fire Boat, you could even put 4 x 6v cells in for longer duration. a single 12v does not give you a lot of maneuvering room regards balance etc. I have just changed my 48" Fireboat to 3s lipo's from 7.2v NimH packs, this is with Graupner 700bb motors with twin 50mm 3 blade brass props, not tested yet due to poor weather and shift patterns, but it sounds great on the bench. Mark

Voltage step down by misterbee Sub-Lieutenant   Posted: 24 days ago
Thanks, Dave, That shows how little I know of these things,.....a 12 volt NiMh is obviously the way to go, Thanks a lot. Onward and upward!!