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farmrjohn
Joined: 31 Dec 2018
Posts: 54
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 Posted: Fri Jan 24, 2020 7:11 pm Post subject: Battery Voltage Under Load, no Charger |
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My search skills are not the best. I've found that a 12 volt battery should indicate 12.8 volts on its own. What voltage should it indicate if it has loads applied to it, i.e. checking out electrical components without the engine running or a charger/external power applied?
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jan 25, 2020 5:48 am Post subject: Battery Voltage Under Load, no Charger |
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At 09:11 PM 1/24/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "farmrjohn" <faithvineyard(at)yahoo.com>
My search skills are not the best. I've found that a 12 volt battery should indicate 12.8 volts on its own. What voltage should it indicate if it has loads applied to it, i.e. checking out electrical components without the engine running or a charger/external power applied? |
It depends on a lot of variables. Size and condition
of battery, state of charge and size of loads. A fully
charged battery in good condition and lightly loaded
will start out at about 12.8 volts and move down
from there. Here's an exemplar discharge plot for
a 17 a.h. svla battery under various loads:
[img]cid:7.1.0.9.0.20200125074029.01f32400(at)aeroelectric.com.0[/img]
As the battery ages the initial discharge voltage falls
and the rate of decay increases illustrating an increase
in internal resistance and loss of capacity.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jan 25, 2020 5:50 am Post subject: Battery Voltage Under Load, no Charger |
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At 09:11 PM 1/24/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "farmrjohn" <faithvineyard(at)yahoo.com>
My search skills are not the best. I've found that a 12 volt battery should indicate 12.8 volts on its own. What voltage should it indicate if it has loads applied to it, i.e. checking out electrical components without the engine running or a charger/external power applied? |
It depends on a lot of variables. Size and condition
of battery, state of charge and size of loads. A fully
charged battery in good condition and lightly loaded
will start out at about 12.8 volts and move down
from there. Here's an exemplar discharge plot for
a 17 a.h. svla battery under various loads:
[img]cid:7.1.0.9.0.20200125074029.01f32400(at)aeroelectric.com.0[/img]
As the battery ages the initial discharge voltage falls
and the rate of decay increases illustrating an increase
in internal resistance and loss of capacity.
Bob . . .
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cluros(at)gmail.com
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| Posted: Sat Jan 25, 2020 9:13 am Post subject: Battery Voltage Under Load, no Charger |
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Do we have a consensus on how charged a battery must be before starting? Is it ok to hand start the engine and charge a very discharged battery with the alternator or is there some point at which a charger must be used? As long as there is enough power left to close the master relay and get the alternator going I've used the engine to charge the battery rather than a charger.
On Sat, Jan 25, 2020, 08:54 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 09:11 PM 1/24/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "farmrjohn" <faithvineyard(at)yahoo.com (faithvineyard(at)yahoo.com)>
My search skills are not the best. I've found that a 12 volt battery should indicate 12.8 volts on its own. What voltage should it indicate if it has loads applied to it, i.e. checking out electrical components without the engine running or a charger/external power applied? |
It depends on a lot of variables. Size and condition
of battery, state of charge and size of loads. A fully
charged battery in good condition and lightly loaded
will start out at about 12.8 volts and move down
from there. Here's an exemplar discharge plot for
a 17 a.h. svla battery under various loads:
[img]cid:7.1.0.9.0.20200125074029.01f32400(at)aeroelectric.com.0[/img]
As the battery ages the initial discharge voltage falls
and the rate of decay increases illustrating an increase
in internal resistance and loss of capacity.
Bob . . .
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farmrjohn
Joined: 31 Dec 2018
Posts: 54
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| Posted: Sat Jan 25, 2020 10:56 am Post subject: Re: Battery Voltage Under Load, no Charger |
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The situation that prompted my question is when I switched the battery on it indicated 12.8 volts. After I turned on the equipment I was working with (lights and radios) I noticed the voltage holding steady at 12.3. Unfortunately I didn't check the amps at that time. After I was done, I switched everything off then started the engine normally and the voltage was up to 14.2 when I switched on the alternator, amps were 6+.
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