Redtop Optima is close to dead

[Corey]

I have heard of his kit.
I just sprung for the Mech Man booster, the one without the LCD.
Will see how it works out, but I am going to run the new Yellowtop for awhile without it and monitor its voltage.

 

[dwh]

I take it what he means by the end is that I will see a voltage drop with the fridge running, well that would be normal correct?

Will still have a voltage drop yes. Whether you see it or not depends on where you measure the voltage.

There might be voltage drop on the fridge circuit, which you might see with a voltmeter connected at the fridge but won't see with a voltmeter connected at the battery, since the meter at the battery bypasses the fridge circuit.

And even if you had meters on both, that wouldn't show you the voltage drop on the air compressor circuit.

So what he means is the gizmo will crank up the charge voltage, but can't do anything about wires being too small for the load they're carrying.

Also can't do anything if the total load on the battery is more than the alternator can supply (can happen while winching), which drags down the battery voltage.

 

[Ducky's Dad]

Quote Originally Posted by Ducky's Dad View Post
The issue not that the alternator output is "too weak" to charge two batteries, but that the voltage is too low to keep some AGMs happy. My old GMC is running a stock 105amp alternator and it has been charging pairs of Optima and Odyssey 34/78s for 20 years. Those batteries never see a shore power recharge or reconditioning unless i do something stupid. It's the voltage that can be a problem on the Toys, not the amperage. This would not be the case if you were running an Odyssey 31, which needs both high voltage and high amperage.

That is kind of what I meant when I responded.

If the voltage is too low for the batteries, it is too low for one or more. AGMs like higher voltages, but most will charge OK with low amperage if you let them charge long enough.

 

[Corey]

Will still have a voltage drop yes. Whether you see it or not depends on where you measure the voltage.

There might be voltage drop on the fridge circuit, which you might see with a voltmeter connected at the fridge but won't see with a voltmeter connected at the battery, since the meter at the battery bypasses the fridge circuit.

And even if you had meters on both, that wouldn't show you the voltage drop on the air compressor circuit.

So what he means is the gizmo will crank up the charge voltage, but can't do anything about wires being too small for the load they're carrying.

Also can't do anything if the total load on the battery is more than the alternator can supply (can happen while winching), which drags down the battery voltage.

Running car stereo amp wire 8 gauge from the Hella 12v outlet in the rear for the National Luna fridge, and it goes straight to the Yellowtop.

If the voltage is too low for the batteries, it is too low for one or more. AGMs like higher voltages, but most will charge OK with low amperage if you let them charge long enough.

I am liking what I am seeing.
Hooked up the solar this morning to the Yellowtop and it was floating around 14.5v.
Fired up the fridge and it cooled down very fast, and loaded it with food for testing.

As seen in the quick video this morning, the fridge is running at 2 Celsius which is where I want it, and the Yellowtop is running at 14.1v with a good amount of sun on the Renogy panel.

Now when I tested this last Sunday, the Redtop would not climb over 11.9v with solar running into it.

So far the new Yellowtop is working out great.
Going to pull the solar panel off later, so the fridge will be only running with the Yellowtop, and no solar input.
I will report back tomorrow when I go out to the rig to go grocery shopping.

And hopefully that MechMan booster I have coming will be topping off both batteries.
You can see my Toyota starting battery is sitting at 12.1v which it has for a long time.
It starts right up and very fast too at that voltage.

 

[Corey]

OK, 15 hours later with the Yellowtop off of solar, the fridge running, the battery was 12.7 this morning.
Not bad at all, considering I have not driven the rig much to put a charge into it beside the solar panel running a bit on it yesterday.
This was with temps around 80 degrees yesterday too.