First attempt at a full scratch build, a 32" Downeast / Lobster boat style hull in ply, to be built to my own design as a picnic / fun boat. Have acquired an MFA Torpedo 500 and a 40mm 4 blade Raboesch prop, 175 series I think. Hoping to run direct drive. Any advice on battery size voltage and Mah to get a turn of speed if required and a reasonable run time. Lipo preferably as I have a 2/3 cell charger from a previous project and limited space only in front third of hull. TX for any advice received
Hi Mate, welcome it the forum, the motor and prop seem ok, a general rule of thumb is prop diameter less than the motor, so you should be ok with this. Your thoughts on batteries, a pair of 2s or 3s lipo's 2200mah in parallel should give you 30 - 40 mins runtime, more if you are kind with the throttle, remember that you must have access to remove the batteries for charging!!! you will also get a reasonable turn of speed but the hull design won't go fast, they are cruising hulls not deep V speed hulls, when testing check for heat either the motor or the ESC, show some pics and lets see how you are doing Mark
put a watt meter on your shopping list please. They are not expensive and will give you an informed idea of the current drawn etc. Remember LIPO batteries should not be discharged below around 3.3V per cell else they DIE.
"that's not a bug its just an undocumented creature."
Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)
Tx for the advice Mark - had been researching and your views seem to back this up - edging towards 2 x 11.1v lipo in parallel 2200mah or slightly bigger dependant on budget. which will be removable. May i ask what "C" rating you would suggest. Not sure my skllls warrant a pic build yet as my 2 previous builds were just modified plastic kits, basically copies of other peoples builds online, not just as testing as this seems to be.
Tx for the info Haverlock - Watt Meter- this is new to me, would this be to check the current drawn off load on the bench etc. I had seen "voltage bleepers" to fit in the boat but again i assume they are not the same. Back to researching
Tx Doug - Looks like another piece of kit to put on the shopping list. Previously had just used a charger from Component Shop and when the lights stopped "blinking" to me that was it. Nothing is ever that simple 😉
The basic of C rating is charge and discharge. ie 2200 mah X 25 max discharge, dont charge above 1amp as it will shorten the battery life and if you are getting close to the 50amp discharge the cells wont last long. The watt meter is fitted in line from the batteries to check what power you are drawing when sailing so giving you an idea about run time. The voltage beepers are needed to protect the cells from being discharged to far, below 3.3 volts and the cells can die. They are fitted into the dallance lead of each battery. There is a deal on ebay for Flurion 3s 2200 lipos £12-99 each i have 4 in use in my RAF Fire Tender with twin 700BB turbo motors, get about 15 mins at full throttle
Hi al, jarvo's answer is more or less correct but not the whole story! Here is a reprint from my attempt to clarify various misunderstandings and misuse of terms related to batteries - usage and maintenance - posted to a thread "battery charging" you can find under 'General Sailing'.
"Hi Both (and all other non-technical guys here!) (Dave_M please jump to the next post or topic!😉) To avoid further confusion amongst the non-technical members can we perhaps straighten out the technical terms involved in battery charging and use (strictly speaking the dimensions or quantities involved). mAh (milli-amphour) is a measure of the capacity of a battery: how many 1/1000 of an ampere (A) it can theoretically deliver in one hour, if in perfect fully charged condition and under perfect environmental conditions. (What you ain't never gonna get!) When the outside temperature drops so does the usable capacity 🤔 Charge and discharge rates are measured in ampere (A). under 1A the milliamp (1A/1000, unit mA) is usually used for convenience. Quality battery packs are marked on the case with maximum charge and discharge rates in A. Sometimes marked as xC/yC. xC is the MAX charge rate and means x times the nominal capacity/1000. yC is the MAX discharge rate (i.e. what your motors take) and often means y times the nominal capacity/1000. Sometimes the max discharge rate is given as a multiple of the max charge rate. See example in my photo. These are MAXIMUM warnings and NOT to be taken as the norm! See example in pic. Capacity 4000mAh = 4Ah, MAX charging current is 8A =2C, (4000/1000)x2. Half an hour charging gives then 8/2=4Ah. I would never ever charge at anywhere near this rate! Charging at 500mA (0.5A) for 8 hours (0.5Ax8h=4Ah) is perfectly adequate and much more gentle on the cells i.e. longer life 😉 MAX discharge current is given as 240A = 30 times max charge current or 60 times capacity in Ah.(4). If I used it at this rate it would probably be irreparably damaged (toasted) in just under a minute (0.9999r) 😡 If any Lixx pack gets HOT while charging or in use take it to recycling pronto, before it sets fire to your boat or workshop/house😡 ALWAYS MAKE CERTAIN THAT YOUR CHARGER IS SET FOR THE TYPE OF PACK YOU ARE USING, NicAD, NiMh, LiPo OR LiION etc (don't forget the balancer connection!). Sorry for teaching some 'grandmas' to suck eggs but having seen so many questions about battery charging and much misuse of the parameter units for batteries in the responses (as above) I felt it was time to clarify things for the non-technical among us, for their own safety and the health of their wallets!" Cheers Doug 😎
Attached Files - Click To View Large
Young at heart - slightly older in other places 😉 cheers Doug
Same as mine from HobbyKing, this type comes in various colours under various names but they are all made by Husang in China😉 You can also connect it between charger and battery to measure the charge (capacity in mAh) you've poked into the battery. This you can then compare with what is taken out again when running or testing motors. 👍
Young at heart - slightly older in other places 😉 cheers Doug