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[bikerdude666]

Been looking at the batteries on component-shop, think im gonna go for 7.2v packs (not sure why, just sort of decided)

It's for a revell flower class corvette fitted with (i think) a monoperm motor, question is....

When some batteries say 3700mAh and others say 5000mAh, am i right in thinking the 5000 will give a longer run time? Want to get a battery pack asap as i've not made it to the lake yet this year, due to lack of battery and charger (anyone recommend a cheap charger aswell?)

Sorry for such a silly question

[DickyD]

You're right, the higher the mAh the longer the run time.

I have two corvettes both running on 7.2V 4600mAh battery packs.

I have one of these for charging my battery packs.

http://www.component-shop.co.uk/html/body_mw6169.html

Its on this page.

http://www.component-shop.co.uk/html/body_radio_control1.html

[bikerdude666]

thanks, out of stock of those chargers atm but they've got the next model up, and it's only £2 dearer, how long a run time do you get on those battery packs? thanks.

[rmaddock]

When some batteries say 3700mAh and others say 5000mAh, am i right in thinking the 5000 will give a longer run time?

Basically, yes.
It's a measure of how much current the battery is able to supply for one hour. a 3700mAh will give 3700mA for a period of one hour, or 3.7 amps in old money.
So, you could run a larger motor for the same time, drawing more current with the "bigger battery" or the same motor for longer.
Some batteries, certainly LIPOs, carry a "C" rating too. That's an indication that it can be discharged faster than it's specified rating without harm. Eg, if your 3700mAh battery had a "C" rating of 2, you could actually drain it at twice the 2.7A rating; 5.4A.

[Paul S]

Bikerdude.

Might be worth double checking which Monoperm you have.  The short case Monoperm Special is rated at 6v 1.5A max (9W) while the Long case Monoperm Super is rated at 6v 3A max (18W).  Would be best to stick an Ammeter in line with it running under load at 7.2v just to check that the prop fitted isn't overloading it.  Nice motors though, they were always expensive but worth it.

Cheers

Paul

[bikerdude666]

and how would i go about checking? it was already fitted in the boat when i bought it, not got an ammeter to test it either, got a 6v lead acid battery here but nothing to charge it with, my bike battery charger only says about 12v not 6v batteries.

[andrewh]

bd666

Thoughts on checking current without a meter:

One - use a car bulb, say a 12V12W bulb which is, of course of 12 Ohm hot resistance and when it is at the "Car" brightness on 12V is taking one amp.
Try it in series with the motor and estimate if it is much brighter or darker than in a car  (Note 7.2 V into 12 Ohm will pass 1.66 Amps)

Two
Fill the DTBM  (Domestic Test Buoyancy Module = bath) with water  - run the motor for a few minutes with your fingers on the case.  If you manage 5 minutes without removing the piggies then the currrent is perfectly comfortable and the prop about the right size 
NOTE - I do not know the Monoperm, but its a high quality 5-pole motor and should no be capable of suffering damage doing this.  If the temperature soars up  - stop
This is a far more severe test than running on a lake, as the propellor is not able to "unload" as the boat moves thru the water.

<<got a 6v lead acid battery here but nothing to charge it with, my bike battery charger only says about 12v not 6v batteries>>
charge the 6V battery with a car bulb in series to drop the voltage a bit using the bike charger .  charge in short stints to avoid overheating and stop when the battery lights the bulb nicely
OR - use disposable batteries

andrew

[bikerdude666]

Hi thanks, I wont have time for a bath test, gotta go to the lake anyway so will just take the corvette down and try it, I'll bring it after a few mins and see if the motors hot, if it is I'll just take it out.

Have to say a huge thanks to the component shop and royal mail, ordered a charger and battery pack yesterday late morning and it got here about half an hour ago!