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traditional alternator - starter battery voltage drops from 14.5 to 13.1 volts when renogy 50S dc mppt charger is connected

mcarver316

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Nov 16, 2022
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Hi,

I've searched and searched for similar topic without much luck.

I have a 2019 ford transit 350 XLT with traditional alternator, renogy dc dc 50S mppt combo and 3 renogy self heating 100 ah lithium batteries setup.

The starter battery voltage is consistently at 14.5 at idle. The starter battery voltage then drops from 14.5 to 13.1 volts when renogy 50S dc mppt charger is connected and alternator charging is activated.

From Renogy 50S manual, the starter battery charging 'cut in' at 13.2 volts in order to charge the house batteries.

Anyone have ideas what is causing the voltage to drop? Thanks!

All lights normal, (alternator, solar, service battery light, battery type). It is charging from alternator, albeit at average of 0.24 amps.renogy-cut-in-voltage.JPG
 
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All modern cars go to 14.3v range right after starting engine, then after a current flow decline, drops to about 13.3 vdc.

If it maintains 14.3v continuously it will overcharge and destroy the lead-acid battery.

If auto has had normal use and battery is in good condition, not having a lot of discharge during off period, it will drop from 14.3v to 13.3v in a minute or two after starting up engine.
 
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All modern cars go to 14.3v range right after starting engine, then after a current flow decline, drops to about 13.3 vdc.

If it maintains 14.3v continuously it will overcharge and destroy the lead-acid battery.

If auto has had normal use and battery is in good condition, not having a lot of discharge during off period, it will drop from 14.3v to 13.3v in a minute or two after starting up engine.
It is dropping to 13.1 when the renogy charger is connected- just below the 13.2 'cut-in' for charging with the alternator to work.
 

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It is dropping to 13.1 when the renogy charger is connected- just below the 13.2 'cut-in' for charging with the alternator to work.
That is because the external charging is providing battery current so the auto's alternator sees a drop off in its required current, triggering it to drop to float voltage.

The Renogy charger will also likely drop to float voltage when connected to a battery greater than about 12.6 vdc.

If you have a clamp-on DC amp meter you can clip it on the alternator output wire or on the battery positive cable while also checking battery voltage to see the action of dropping battery current correlation to dropping to float voltage by alternator.

That alternator must make the decision by current delta as it must handle the situation where you immediately turn on headlight loads so that the battery does not get locked into a constant absorb level voltage charge.
 
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That is because the external charging is providing battery current so the auto's alternator sees a drop off in its required current, triggering it to drop to float voltage.

The Renogy charger will also likely drop to float voltage when connected to a battery greater than about 12.6 vdc.
So how do I get the renogy dc charger to charge the house battery as it is supposed to?

I've tried charging at full, 75%, 65%, 35% house battery state of charge and still no luck triggering the charging threshold.
 
So how do I get the renogy dc charger to charge the house battery as it is supposed to?
It is doing what it is supposed to do.

If you run the battery down below 12.5 vdc for rested open circuit voltage, then connect charger, it will trigger a full charge cycle to 14.4v absorb.

If you have a bad battery, with high internal resistance, the voltage will jump up as soon as charge current is applied and the charger will drop to float voltage. It may indicate a bad battery triggering a red LED light on charger and shut down charging.
 
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It is doing what it is supposed to do.

If you run the battery down below 12.5 vdc for rested open circuit voltage, then connect charger, it will trigger a full charge cycle to 14.4v absorb.

If you have a bad battery, with high internal resistance, the voltage will jump up as soon as charge current is applied and the charger will drop to float voltage. It may indicate a bad battery triggering a red LED light on charger and shut down charging.
Seems odd the house battery can only be charged from the alternator when house battery is nearly completely discharged

All lights on the renogy dc50s is normal - steady red for alternator charging, steady amber for service (aka house) battery and steady blue for battery type (lithium).

Charging from solar is working properly, charging amperage rising or lowering depending on available sunlight.

I am draining the house battery now and hope the alternator charging is triggered at 12.5 vdc. For this test I am leaving the solar disconnected to ensure it is charging exclusively from the alternator/starter battery.
 
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Seems odd the house battery can only be charged from the alternator when house battery is nearly completely discharged
Nothing I said implies this statement. 12.50 vdc rested open circuit voltage on a 12v, six cell, lead acid battery is about 80% state of charge.

You do not want to continuously recycle a full absorb cycle on a battery. It is stressful on battery.

Most PV charge controllers prevent repeated retriggering of a full absorb cycle by using a timed absorb cycle and preventing a repeat of a new absorb cycle for some time period, unless battery drops to a significantly low voltage level for a fixed time length. This is to prevent a surge load from inverter causing a momentary battery voltage slump triggering a repeat absorb cycle too often. Maintaining float voltage is okay and will keep battery near fully charged.

Auto's always initiate a short absorb cycle when starter is run to replenish the starting consumption and prevent sulfation of battery.
Specific Gravity and acid percent Chart.png
 
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Nothing I said implies this statement. 12.50 vdc rested open circuit voltage on a 12v, six cell, lead acid battery is about 80% state of charge.

You do not want to continuously recycle a full absorb cycle on a battery. It is stressful on battery.

Most PV charge controllers prevent repeated retriggering of a full absorb cycle by using a timed absorb cycle and preventing a repeat of a new absorb cycle for some time period, unless battery drops to a significantly low voltage level for a fixed time length. This is to prevent a surge load from inverter causing a momentary battery voltage slump triggering a repeat absorb cycle too often. Maintaining float voltage is okay and will keep battery near fully charged.

Auto's always initiate a short absorb cycle when starter is run to replenish the starting consumption and prevent sulfation of battery.
View attachment 139684
Are you saying I need to run down the starter battery to 12.5?

It is still odd that Renogy DC 50S 'cut in' voltage from the starter battery is 13.2, when it is already maxed out at 13.00. Thus, it will never be triggered with this logic. Renogy should have set the 'cut in' at 12.5 in order to not run down the starter battery.

Update: resting volt on starter battery with ignition off is 11.8 volts. At idle, 13.1. At speed driving around, 13.1. This is with dc charger connected.

With the dc charger disconnected, starter battery is at constant 14.5 volts, whether at idle or at speed.
 
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starter battery is at constant 14.5 volts
That’s not abnormal for a lot of vehicles, particularly older ones, with fla batteries. My 89 jeep often runs in the low 14’s. That’s the result of the alternator- not physical rested battery voltage.
 
That’s not abnormal for a lot of vehicles, particularly older ones, with fla batteries. My 89 jeep often runs in the low 14’s. That’s the result of the alternator- not physical rested battery voltage.
Yes 14.5 is normal- it drops to 13.1 volts when the renogy dc charger activates. 'Cut in' or threshold for the starter battery to charge the house battery as programmed by renogy is 13.2 volts.
 
drops to 13.1 volts when the renogy dc charger activates
That may be the result of the ‘net load’ the DC2DC charger places on the battery. I’d think alternator would compensate but maybe not? Is the battery up to par on load testing and resting voltage? Those are my questions.
On a lot of newer vehicles 14.4V might be a bit high. If the battery is weak or a bad connection that may be fooling the alternator voltage controller.

I’m at a loss beyond just noting that 14.4V isn’t necessarily unusual in a vehicle, becoming less normal for ten years or do now, and increasingly less normal as the calendar goes by.
 
That may be the result of the ‘net load’ the DC2DC charger places on the battery. I’d think alternator would compensate but maybe not? Is the battery up to par on load testing and resting voltage? Those are my questions.
On a lot of newer vehicles 14.4V might be a bit high. If the battery is weak or a bad connection that may be fooling the alternator voltage controller.

I’m at a loss beyond just noting that 14.4V isn’t necessarily unusual in a vehicle, becoming less normal for ten years or do now, and increasingly less normal as the calendar goes by.
New OEM ford starter battery installed a week ago by ford dealership. The van went in for 60K maintenance service package, including testing battery connections, load and resting voltages and ensuring they are to factory operating specs.
 
Nothing I said implies this statement. 12.50 vdc rested open circuit voltage on a 12v, six cell, lead acid battery is about 80% state of charge.

You do not want to continuously recycle a full absorb cycle on a battery. It is stressful on battery.

Most PV charge controllers prevent repeated retriggering of a full absorb cycle by using a timed absorb cycle and preventing a repeat of a new absorb cycle for some time period, unless battery drops to a significantly low voltage level for a fixed time length. This is to prevent a surge load from inverter causing a momentary battery voltage slump triggering a repeat absorb cycle too often. Maintaining float voltage is okay and will keep battery near fully charged.

Auto's always initiate a short absorb cycle when starter is run to replenish the starting consumption and prevent sulfation of battery.
View attachment 139684
Suffice to say running the house battery down to 12.4 volts still didn't trigger higher amperage charging. No bueno from alternator charging.
 
Does your van have another charging circuit for the house battery? Many stock systems have a simple relay that connects the house and starting batteries together when the engine is on. If you have one of those, you probably need to disconnect it.
 
Does your van have another charging circuit for the house battery? Many stock systems have a simple relay that connects the house and starting batteries together when the engine is on. If you have one of those, you probably need to disconnect it.
Thanks- The renogy dc50s is connected to the CCP2 (ford transit Customer Connection Point) on the left side of the driver seat- It is as direct connection to the starter battery as it can be.
 
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The replies seem to concentrate on lead acid batteries, as I understand the house batteries are three 100Ah Renogy batteries. These batteries in parallel will easily take the 50 amp charge from the DC to DC charger. The DCC 50 set for lithium charging has an output boost volts of 14.4, no float duration or voltage, and a boost return of 13.2 volts at the house battery. Thus unless the house battery falls to below 13.2 it will not enter a further boost charge cycle.
The stated voltage at the starter battery with the DCC 50 connected is, ign off, 11.8, engine running,13.1. With the DCC50 disconnected, the starter battery reads 14.5 volts.
Ignoring the performance of the DCC50 and assuming these voltage measurements are correct, they indicate an issue with the Ford system.
It's important with recent vehicle that additional loads are connected to starter battery positive via a suitable fuse, or the connection point on the seat pedestal ( Transit) and the negative to vehicle metal/frame/ chassis. The negative should not connect to the starter battery negative post. ( the vehicle may have a sensor in the negative link to metal)
Thus in this application the negative of the DCC50 connects to vehicle metal as does the negative of the house battery.
Note the Transit up converters manual limits the auxiliary continious current take off to 70 amps.

Summary, the DCC 50 connected correctly should not significantly load the vehicle battery.

Mike
 
The replies seem to concentrate on lead acid batteries, as I understand the house batteries are three 100Ah Renogy batteries. These batteries in parallel will easily take the 50 amp charge from the DC to DC charger. The DCC 50 set for lithium charging has an output boost volts of 14.4, no float duration or voltage, and a boost return of 13.2 volts at the house battery. Thus unless the house battery falls to below 13.2 it will not enter a further boost charge cycle.
The stated voltage at the starter battery with the DCC 50 connected is, ign off, 11.8, engine running,13.1. With the DCC50 disconnected, the starter battery reads 14.5 volts.
Ignoring the performance of the DCC50 and assuming these voltage measurements are correct, they indicate an issue with the Ford system.
It's important with recent vehicle that additional loads are connected to starter battery positive via a suitable fuse, or the connection point on the seat pedestal ( Transit) and the negative to vehicle metal/frame/ chassis. The negative should not connect to the starter battery negative post. ( the vehicle may have a sensor in the negative link to metal)
Thus in this application the negative of the DCC50 connects to vehicle metal as does the negative of the house battery.
Note the Transit up converters manual limits the auxiliary continious current take off to 70 amps.

Summary, the DCC 50 connected correctly should not significantly load the vehicle battery.

Mike
Everything you mentioned checks.

I've tested the batteries individually (even tested an agm one separately and changed the profile to agm). Somehow still getting the same result. I am beginning to think something went wrong with the way Ford alternator manages the voltage between the starter battery and house battery.
 
Just try a run directly off the battery to the DC2DC charger.
Sometimes I think the old starter solenoid triggered at key-on to charge accessory batteries is the best. Not sure if the lithiums would suck too much juice to do that, though.
 
Solved! Victron Orion standalone DC DC charger solved the problem- The Victron has better software working with the alternator/starter battery. Both the Renogy DCC50S and Redarc 1250D failed to work.

I don't mind buying a separate mppt from Victron- which I will do- since the Victron just works.
 
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