Will a 100ah battery damage a dc motor

Thread Starter

smilegr8

Joined Nov 10, 2020
5
Hi everyone
I assume this is a daft question but if you have time please help

I have a 100ah leisure battery and want to connect a dc motor /air blower .
On the blower i can see the wattage (24w) 12v and the blower needs to be wired with a 5amp fuse .

My question is - would it be ok to simply wire it via a switch with a fuse inline or it needs more bits to be added to operate safely and correctly?
Since the battery has 100ah - will that be too much for the dc motor? Or thats just the capacity and the motor "takes" only the required amount of amps to operate?

At least if you can direct me to a page where i can start to educate myself as have no electrical knowledge

Many thx
 

OBW0549

Joined Mar 2, 2015
3,566
Since the battery has 100ah - will that be too much for the dc motor?
The motor isn't going to give a fat rat's patootie about the amp-hour capacity of your battery; it will simply run twice as long as it would with a 50 a-h battery. Power sources don't ever force current into a load; they just establish a voltage and the load resistance determines how much current the load will draw at that voltage.

Or thats just the capacity and the motor "takes" only the required amount of amps to operate?
Correct.
 

crutschow

Joined Mar 14, 2008
27,750
I foolishly believed that i need to add a resistor in line just like the led strips have
Most electrical devices, such as motors, are voltage operated and only take the current they need.
An exception to this are LEDs, which are current operated devices (although they do have a small voltage drop), and will take way too much current if they are connected directly to a voltage source without something to limit the current.
 

WBahn

Joined Mar 31, 2012
26,398
Hi everyone
I assume this is a daft question but if you have time please help

I have a 100ah leisure battery and want to connect a dc motor /air blower .
On the blower i can see the wattage (24w) 12v and the blower needs to be wired with a 5amp fuse .

My question is - would it be ok to simply wire it via a switch with a fuse inline or it needs more bits to be added to operate safely and correctly?
Since the battery has 100ah - will that be too much for the dc motor? Or thats just the capacity and the motor "takes" only the required amount of amps to operate?

At least if you can direct me to a page where i can start to educate myself as have no electrical knowledge

Many thx
What is the terminal voltage of the battery? If it is much more (or much less) than 12 V, you could have a problem.

Assuming it is 12 V (which I'm guessing it is), then a 100 Ah battery should have sufficiently low internal resistance to deliver the few amps that the blower seems to require.
 

MisterBill2

Joined Jan 23, 2018
9,294
Very specifically, as others have mentioned, the 100Amp Hours is a rating of capacity, meaning how much charge the battery can deliver. It is the voltage rating that matters. So if the battery is a 12 volt batters, at the 2 amp draw of the fan, you should be able to run it for at least 50 hours before needing to recharge the battery.
So the question was not really daft, just rather uninformed. But now you know!
 

Thread Starter

smilegr8

Joined Nov 10, 2020
5
Thank you to all the above, prompt replies!
And i assume the 5amp fuse is only to protect the circuit in case of short circuit? Am i right ? As initially i thought it needs a fuse due to the battery amperage
 

Ian0

Joined Aug 7, 2020
3,268
Very specifically, as others have mentioned, the 100Amp Hours is a rating of capacity, meaning how much charge the battery can deliver. It is the voltage rating that matters. So if the battery is a 12 volt batters, at the 2 amp draw of the fan, you should be able to run it for at least 50 hours before needing to recharge the battery.
So the question was not really daft, just rather uninformed. But now you know!
But make sure to recharge it after 25 hours, because completely discharging lead-acid batteries severely reduces their life!
 

Thread Starter

smilegr8

Joined Nov 10, 2020
5
But make sure to recharge it after 25 hours, because completely discharging lead-acid batteries severely reduces their life!
I will - the battery is gonna be connected to a solar panel in line with a simple charge controller

Thanks again !
 

Audioguru again

Joined Oct 21, 2019
3,543
A motor draws a massive current if something stops it from turning, including when it is first turned-on. The high current is its rated "stalled current". Maybe that is why it is fused.
 

WBahn

Joined Mar 31, 2012
26,398
Thank you to all the above, prompt replies!
And i assume the 5amp fuse is only to protect the circuit in case of short circuit? Am i right ? As initially i thought it needs a fuse due to the battery amperage
The fuse is there to guard against failures or other conditions that would draw excessive currents (including short circuits). The 5 A rating likely allows not only for a margin above the nominal 2 A draw, but also for transient currents during start up.

Think of the Ah rating of a battery like the size of a fuel tank. If you have an engine that consumes 2 gallons per minute, you wouldn't be concerned that a 100 gallon tank is going to force too much fuel into the engine.
 

Ian0

Joined Aug 7, 2020
3,268
Think of the Ah rating of a battery like the size of a fuel tank. If you have an engine that consumes 2 gallons per minute, you wouldn't be concerned that a 100 gallon tank is going to force too much fuel into the engine.
That’s a very good analogy.
It still wouldn‘t force too much fuel into the engine if the output of the tank were on a 4” pipe. (Analogy for the amount of current the battery could deliver)
 

Thread Starter

smilegr8

Joined Nov 10, 2020
5
Wow guys - so many important things i didn't even consider until now Thanks very much for you time .

Now i will only need to figure out the correct size / diameter of the wire to prevent voltage drop as the blower will be fitted in a room about 20-25m from the battery .
I think there are online calculators for that
 

crutschow

Joined Mar 14, 2008
27,750
The fuse is to protect the wire from starting a fire if there is a short circuit.
The fuse rating is normally based upon the wire size.
 

Ian0

Joined Aug 7, 2020
3,268
Think about how your house is wired and the appliances that you use. The fuse in the fuse box protects the cable, the fuse in the appliance protects the appliance. (And in Britain and Ireland the fuse in the appliance’s plug protects the appliance flex)
 

WBahn

Joined Mar 31, 2012
26,398
The wire size puts an upper limit on the acceptable fuse size. Smaller fuses should be used based on the load characteristics, if known.
 

MisterBill2

Joined Jan 23, 2018
9,294
For a 75 foot run, the conductor length being "there and back", and the load being 2 amps, and the voltage drop during startup not mattering, I suggest #16 wire, unless cost is an issue, in which case #18 should be OK.
 

Bernard

Joined Aug 7, 2008
5,788
About 25 m of 2 conductor wire so 50 m of wire. Assume that .5 ohm acceptable then try # 18 @ 6.39 ohm/1000m = .3 ohm for fan.
Measure DC resistance of motor, a similar motor, Johnson HC613G-6411
measures about .4 ohm giving a start I of about 30 A which would take out a 5A fuse unless it was rated as Slow-Blow. Running current 1.5A @12V.
 
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