Batteries and power consumption

[poledark]

Could someone please explain (in simple words) a bit about batteries. I have a homemade electric barrow, and it has worked well for a couple of years. The speed/power was controlled by a circuit board and resistor(?). This governed the amount of power(speed) that the barrow moved. On level ground very little power(current? ) was used, but when going up hill I turned the power full on.

 

As I said, no problems............

 

Last week i went thro some pretty tough brambles and somehow the chain drive came off and jammed the motor, not knowing what had happened I turned the power up full and shoved my way through. Cut a long story short, I burnt out the control board. Approx £50 for a new one (if they are still available)

 

So I decided to gear the barrow down, so that I give it a push start and switch on the power.................lovely jubbly, it runs beautifully at a nice steady walking pace fully loaded

 

I spoke to the guy who supplied the motor etc and he said it would do no harm provided I didn't let the motor stall for too long i.e. "give it a push before you switch on"

 

What I want to know is this..will the battery last longer with the lower gearing, or will it use more power. Looking at it simply I feel that as when riding a bike it is easier to peddle in a lower gear, then probably the battery/motor is also finding life easier.

 

Den

Edited June 23, 2008 by poledark

[Newt]

You will almost need to put a meter in the circuit for a bit to measure the amps being used by the motor Den.

 

I will try to get a more specific answer from an RV forum that has some serious battery experts. The topic is at

http://www.rvforum.net/SMF_forum/index.php?topic=17601.0

 

As another battery note - you will get the most possible battery by using a pair of 6v golf cart batteries hooked in series so they are delivering the 12v your motor needs (at least I imagine it is a 12v). They will have a higher initial cost that any 12v but the amount of available power and the number of times they can be recharged even if you run them flat is way better.

 

My next aux battery on the boat will be a pair of them rather than a single deep draw 12v.

[chesters1]

everythings a trade off in physics ,using a resistor to control speed just means that power is wasted in heat from the resistor (hopefully its a large ceramic one).

car batteries are very good at supplying large amount of amps for a very short period but just hate being deep discharged ,leisure (or marine) batteries dont mind deep discharging (its preferable you try not to though) but most don't like large amps being used ,you can get middle of the range ones that can take both but they are not that good.

Gel batteries are far better than flooded (the usual acid/lead batteries) but cost more.

the biggest thing though is how its charged ! most car battery chargers are little more than primitive 240v to 12v (well c14v really) transformers which just chuck volts and amps into a battery until its charged.crude but to the run of the mill user perfectly ok but its not good for the battery.in time the plates get distorted using a high ampage charger or get a buildup of salts using a low ampage one (or a trickle charger).also some chargers can never fully charge a battery because of the resistance of the battery itself (applies to nimh and nicads too) so your battery will show 12v (or whatever the small batteries are) but in reality 12v batteries are 13.8v fully charged! the ampage counts not the volts .

theres smart chargers available now that "recondition" batteries then monitor the voltage and top it up when needed but using high frequency rather than brute volts and amps,i have a Ring 16 amp charger that can handle batteries up to 200 amps theres other versions for smaller car type batteries.since i bought it i have definitely noticed the battery under the same conditions lasts far longer than it did (we have a 110amp in the trailer tent for 12v devices) so the money was well spent considering the price of batteries today!!

its the same as those higher and higher voltage drills now on the market ,24v? it means nothing if it contains nothing more than small batteries joined together to make 24v ,its what the capacity in amps is not the voltage! a 12v drill with better batteries that hold more amps will be more powerfull and last longer than one that has no capacity but large volts!

motors also get hit hard by physics theres 12v motors and 12v motors ,the cheap versions have thinner wires which are just tolerating the amps flowing through them they work fine enough for most things but burn out easily ,the good ones have thicker wires which use more amps but last longer and have more grunt.

gears are good for controlling things but the more there are the more resistance to them turning ,resistance by the teeth themselves and the resistance by whatever they are moving so gears need more amps to turn them the more there are!.

as Newt says seeing what the current drain is is best to see which setup works best a simple multimeter set at amps in line (positive lead to battery neg to motor) will do or buy a pukker one for your trolley but remember if your motor is struggling it maybe using more amps than you think 12 amps running through a 10 amp max meter may result in dead meter!

the golf cart batteries Newt mentions are probably a good idea ,probably gel type and for their size probably hold more amps so two together will be better (maybe) than a car battery but probably need a better charger than a car one so i would plump for a smart charger anyway which can handle gel batteries as well as flooded.make sure also the charger can handle the capacity (amps) of the battery you use i have a smart charger for small batteries too but it cant handle batteries above 30 amps hence i bought the larger one for my leisure battery.

 

rather than buying a new controller Den cant you fix the old one? typically they are made from components readily available (unless its unusually high tech which i doupt) from maplins etc so finding (not always the easiest thing) the component that failed and putting in a new one would be far cheaper most things (not all unfortunately) can be fixed when your a tight bugger like me even in this throw away age we live in although nowadays the boxes they are in are not designed to open like they used to be so the end result may not be as perfect to the eye as it was new.

 

when buying any "leisure" type batteries look at the very small print some can be discharged and recharged many more times than others typically though the more charges the more you pay so treating you battery with respect from the outset can save a few quid in the long run ,gassing batteries especially in "sealed" ones is not good (nothings really "sealed" they have vents which let out gas - gas doesnt come from nowhere its your acid and plates eventually the level drops untill the battery is unusable) so traditional old fashioned flooded batteries with removable plugs are far better for long use if you can find them if you use flooded rather than gel batteries.

if buying a second hand battery (noted by my own experience ) dont trust the magic eye! it works on only one cell (so you could have a dead cell anywhere else)so always use a meter!! anything over 12.5v is probably fine!reject anything else below that!

Edited June 24, 2008 by chesters1

[poledark]

Thanks....I will read again when I return from fishing this evening. The battery is a "golf cart type Newt..supplied and fitted to thousands of golf buggies. I have no problem with power, loads of it to spare, I just wondered about the consumption for a given distance ?

 

Den

[ColinW]

Power = torque x rpm (x a constant)

If the gearbox doubles the rpm it will halve the torque, so the power stays about the same (assuming the gearbox is pretty efficient!)

As long as the motor is running at a "sensible" speed the battery life shouldn't change much.