Voltage drops when cranking...
- Thread starter CraigH
- Start date
sgkent
Lawn Addict
- Joined
- Sep 27, 2017
- Threads
- 30
- Messages
- 1,679
Maybe Bert, Walt, Star Tech or one of the other techs here could tell you if that is normal or not on a new battery. A 2V drop sounds excessive to me - like the starter is pulling too much current. Unless the engine is hard to turn by hand with the plugs out. I would think it would just spin like crazy when the plugs are out. This assumes that the PTO belt is somehow not engaged.
Excessive amp draw with no spark plug in. Should be about that ready to mow, 10.8vdc while cranking.
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 65
- Messages
- 24,809
Way back in reply #1 it was suggested that the compression release was probably the problem
Then in reply # 7 the cam was again suggested to be the villian .
Then the thread wandered off because of numbers on a DVM
I never use one apart to test the output from the alternator & diodes as numbers just confuse things as has happened here because people do not understand the significance of the numbers.
In your case the 2 minute test which you had already done is to get a pair of jumpers and a known good battery , ie your vehicle .
You then bypass your mowers wiring by jumping directly from the battery to the starter motor
If the starter fails to turn over the engine then you do the same from the known good battery
As that failed to turn over the engine then either the starter is bad or the cam is bad , which is why Illengine suggested the cam back in reply # 1
The 2 minute test for a bad cam / mal adjusted valve lash is to try cranking without the spark plug as you had done .
So cranks no plugs won't crank with plugs = reset valve lash carefully & try again.
Same results = stuffed cam
You verify the cam by removing the rocker cover , adjusting the valve lash then rotate the engine watching the rockers .
In your case the inlet should reopen a tiny amount just before the piston gets to the end of the cylinder .
To check the compression relief against wear, you close down the inlet valve lash.
You can go as tight as 0.002" without seriously affecting the performance of the engine, but that is of course a stop gap to get you by till the new cam arrives or till the end of the season
AS for dropping battery voltage under heavy discharge, this is quite normal and happens when the current draw exceeds the discharge rate of the battery
The discharge rate is a function of the plate geometry & metallurgy , the paste chemistry & grain size, the bonding agent used for the paste, the electrolyte & the busbars that connect all the plates together and the temperature of the battery & wires .
The main purpose of carbon pile load testers is to sell confused customers new batteries and I am yet to see an auto parts store use one correctly .
Most mowers use # 4 ( Top end ) # 6 ( bulk of brands ) or # 8 ( cheapies ) gauge wire, usually 25 to 42 strand .
The current capacity of that wire is roughly 45A, 35A or 25A respectively so shoving a 200 +A load from a carbon pile across the terminals is pointless because the wires can not carry that load and the starter will never draw those sort of amps unless there is a dead short .
Then in reply # 7 the cam was again suggested to be the villian .
Then the thread wandered off because of numbers on a DVM
I never use one apart to test the output from the alternator & diodes as numbers just confuse things as has happened here because people do not understand the significance of the numbers.
In your case the 2 minute test which you had already done is to get a pair of jumpers and a known good battery , ie your vehicle .
You then bypass your mowers wiring by jumping directly from the battery to the starter motor
If the starter fails to turn over the engine then you do the same from the known good battery
As that failed to turn over the engine then either the starter is bad or the cam is bad , which is why Illengine suggested the cam back in reply # 1
The 2 minute test for a bad cam / mal adjusted valve lash is to try cranking without the spark plug as you had done .
So cranks no plugs won't crank with plugs = reset valve lash carefully & try again.
Same results = stuffed cam
You verify the cam by removing the rocker cover , adjusting the valve lash then rotate the engine watching the rockers .
In your case the inlet should reopen a tiny amount just before the piston gets to the end of the cylinder .
To check the compression relief against wear, you close down the inlet valve lash.
You can go as tight as 0.002" without seriously affecting the performance of the engine, but that is of course a stop gap to get you by till the new cam arrives or till the end of the season
AS for dropping battery voltage under heavy discharge, this is quite normal and happens when the current draw exceeds the discharge rate of the battery
The discharge rate is a function of the plate geometry & metallurgy , the paste chemistry & grain size, the bonding agent used for the paste, the electrolyte & the busbars that connect all the plates together and the temperature of the battery & wires .
The main purpose of carbon pile load testers is to sell confused customers new batteries and I am yet to see an auto parts store use one correctly .
Most mowers use # 4 ( Top end ) # 6 ( bulk of brands ) or # 8 ( cheapies ) gauge wire, usually 25 to 42 strand .
The current capacity of that wire is roughly 45A, 35A or 25A respectively so shoving a 200 +A load from a carbon pile across the terminals is pointless because the wires can not carry that load and the starter will never draw those sort of amps unless there is a dead short .
sgkent
Lawn Addict
- Joined
- Sep 27, 2017
- Threads
- 30
- Messages
- 1,679
Bert - his engine does not make it a full turn with a new battery fully charged and the plugs removed. The voltage falls to 10.2V at the actual battery terminals. To me that sounds like excessive draw at the starter. With the plugs removed and measuring at the actual terminals, I don't see how the cam or cables could be of issue. He has not confirmed that the engine turns freely by hand, or I missed it.
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 65
- Messages
- 24,809
Actually , my bad got this one mixed up with another one.
But he has used jumpers from a known good battery which made no difference.
IF a starter is energised but does not turn then the armature is a direct short across the battery so the voltage will drop .
Get one like this. Must fit in your battery tray. Same terminals are easy to match up at battery store. Or look in your manual for proper battery part number/type.
Get the lowest CCA rating you can. Should have thicker lead plates providing longer battery life. Case in point, the battery picture from walmart. They have the same mower battery in 330 and 230cca's. Get the 230cca battery.
Pull the starter off the engine. Bench test it with a jump pack and jumper cables. Measure the voltage drop when cranking. Should be minimal with heavy gauge cables and a large battery source. If you are still getting 9 and 10vdc in free air, starter is toast.
Also measure voltage drop across starter solenoid, while cranking. Contacts could be getting smoked drawing excessive current.
Also measure voltage drop across starter solenoid, while cranking. Contacts could be getting smoked drawing excessive current.
The engine spins over absolutely fine with the plug removed.
As mentioned a few posts back, I've replaced battery with a u1r 12v 30ah 330cca, it's all I could get as we don't have alot of choice off the shelf in this country like you may do, ride on mowers and ATVs (which use these batteries) aren't very common over here hence the lack of support from my side of the pond.