New Lifepo4 105ah load test readouts
- Thread starter pghebikes
- Start date
harrisonpatm
10 kW
- Joined
- Aug 8, 2022
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- 885
It does seem dramatic, but it ultimately depends on the cell. Do you have a spec sheet for it? Or at least capacity?
If you read a higher voltage at the battery than the load, your connections and/or wiring between battery and load are insufficient for the load.pghebikes said:
Or the voltmeter on one or the other is incorrect; you can verify that by turning off the load to see if they then both read the same. If they do, you can use your voltmeter to measure across one of the wires from battery to load, and it will then read part (probably half) the voltage difference between the batteyr measurement and the load measurement.
pghebikes said:
A cell "rated" for something could certainly sag very low under minimal load if it's defective, damaged, old, etc...but it would read the same at the battery as the load.
In your case, the readings you get are from two different voltmeters, at the same time? If so, you must test to see if they read the same under no load, or the same while measuring the same point thru the same set of leads at the same time.
This means you either have a problem with the meters (one or both), or with the leads from the battery to the load, or the connections at either battery or load.
The most likely is that the wires for your test leads are too thin for the current you are drawing with the load, and that the connection method to the load is too high a resistance.
So, you need to test to verify where the problem lies. It should only take a minute or two at most.
As noted above:
Bbbbrass
1 W
I’ve had that exact issue. Use 8 gauge wire and lugs, not alligator clips.
Hillhater
100 TW
The reading at the load is NOT battery sag.pghebikes said:
Sag is the difference between cell voltage with no load, and cell voltage under load.
The 2.6 volts at the load is just highlighting the resistance of the connection leads and clips.
You are just measuring thin wire resistance
Put in a thick enough wire - and well crimped lugs, whole path very low resistance
so that voltages under load all read the same at every point in the circuit.
then pick ONE spot each for +/- and use a data logger to plot the Amps vs Vdrop curve and the Ah used integrated against Vdrop.
Put in a thick enough wire - and well crimped lugs, whole path very low resistance
so that voltages under load all read the same at every point in the circuit.
then pick ONE spot each for +/- and use a data logger to plot the Amps vs Vdrop curve and the Ah used integrated against Vdrop.
Bbbbrass
1 W
BVH said:
Due to the voltage drop, it’s only like 55 watts. IF he had better lugs he may have had more current and had issues.
Hillhater
100 TW
Actually, the energy dissipated in the connections is only about 13W…!Bbbbrass said:
0.6 volt drop x 21 A ….the remainder 2.6v x21 A, (55 W) , is dissipated in the load.
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