DC-DC Charge controller or alternator issue

[Coloradojeep]

I've got a 1992 Bluebird TC2000 with the 5.9 Cummins and a renogy 50 amp dc-dc mppt charge controller. I've had everything wired for over a year and ask has worked well as it was supposed to until recently. I'm still building the bus out so it's not in full use yet. With the bus running at idle it trajectory about a minute and then the DC- DC charger starts charging the house batteries. I can see the ankle go up on the battery monitor, charging about 25 amps. After about 30 seconds it stops, then about 20 seconds it starts again it does this until I disconnect the charge controller and the alternator operates just fine. Any ideas?

It seems this started after the dc-dc charge controller would drain the bus battery down enough after the bus was turned off that I would have to charge the batteries again, when it's cold to start the bus.

 

[Albatross]

That sounds like you've got some kind of incompatible setting somewhere. Of course, it may not be a setting, as it could be an incompatibility between the DC-DC charge controller, and whatever it is that you've got on the house batteries.



Essentially, you've got setting on the (house?) battery-monitor that says, "sure, I could use a top-off", and it opens a connection; the DC-DC charger ramps up like a kid that just learned how to run, and then the battery-monitor says, "whoa whoa whoa, slow down, hoss... Not that fast mmkay?" and shuts the thing down. System resets, and then starts up all over again.



This is likely to be caused by some kind of incompatible battery setting--or lack of one--on the DC-DC charge controller. The DC-DC gear is probably aimed towards a PbSO4 battery, and your house batteries and charge-controller are likely designed for a Lithium-battery, which is a bit more sensitive at the top end.

 

[Rucker]

Couple of questions-
-I've not heard of an MPPT DCDC charge controller. What model/brand is it?
-Is the charge controller wired so it only charges when the bus is running? (on a Renogy, I think it's a white wire connected to the 12VDC 'run' circuit)
-Did you ever monitor the charge controller when it was first installed, and if so does it operate differently now? I ask because my NOCO battery charger cycles like that as part of its normal operation. Maybe that's how it's supposed to work?

 

[Coloradojeep]

Renogy 12V 50A DC to DC Battery Charger with MPPT, On-Board Battery for Gel, AGM, Flooded and Lithium Batteries, Using Multi-Stage Charging, Solar Panel and Alternator https://a.co/d/9kCRm8t

It starts to charge once it sees 13.2 volts and stops once the voltage drops below 12.7 volts. Doesn't really matter if the bus is running or not. Though it won't charge at the 50 amps unless the bus is on.

 

[cadillackid]

is it possible that the wiring to the charge controller has a voltage drop such that it goes below 12.7 under load and shuts the renogy off? then at no load the voltage rises back up, renogy kicks in.. rinse and repeat..
at 50 amps you need some pretty good wire esp if there is any sort of distance between the alternator and the renogy..



if this is a decent length bus at a minimum you need 4 or 2 gauge wire... .. I ran 4/0 welding wire to the rear of my bus and under heavy loads still habe a bit of a voltage drop.. not bad but it is noticeable on a meter..

 

[AlphaHare]

Do you have a fixed voltage alternator, or a smart alternator? One variable to eliminate or explore.

 

[Coloradojeep]

Fixed voltage. 2 awg wire over about 35 feet. I think I may have found my problem though. I used a 50 amp breaker, I'm going to swap it out with a 60 amp. It's only tripped the breaker once that I can think of but it did it as I was working on things last night.

 

[Jono14]

If it is an auto-resetting thermal breaker then you could be right. Because the on-off cycle is happening so quickly, you should be able to monitor the voltage right at the input terminals of the DC-to-DC with a volt meter.
If it is the breaker, you should see voltage go to zero and return. If it is voltage drop that cadillackid describes, you should be able to see that as well.

I am also interested in your last statement about the dc-to-dc charger draining the bus battery. It seems the 12.7 shutoff may be a bit too low. For Victron's DC-to-DC charger, they use a default of under about 13.2 iirc and wait for 14.0V to start up immediately (or 13.8 to start after a delay).
A fully charged LA battery could sit up over 12.7 for a while and you do want the dc-to-dc to shut off right away when the engine is off - so you may want to raise those values up a bit. You can play around with the settings and then use the voltmeter to watch its performance.

The more elegant way to address shutoff is to use an ignition wire to turn the unit on and off if it has that option (as Rucker questioned). But that can sometimes be a hassle to find a good source.

 

[Coloradojeep]

https://youtu.be/jQYdp67HHr8?si=OwfLG0rIqx4rNxOt

Swapped out to a 60 amp breaker. No difference. Everything works great at 25 amps but at 50 amps it still only holds 50 amps for about a minute then it starts pulsating. Tried a higher rpm and no difference.

I'm not sure I can change the starting and stopping of the DC charge.
I do have a latching solenoid to wire in to disconnect the house and starting batteries when the bus is off. This is only going to be an issue during the winter when I'm not getting any sun here in the PNW.

 

[cadillackid]

https://youtu.be/jQYdp67HHr8?si=OwfLG0rIqx4rNxOt

Swapped out to a 60 amp breaker. No difference. Everything works great at 25 amps but at 50 amps it still only holds 50 amps for about a minute then it starts pulsating. Tried a higher rpm and no difference.

I'm not sure I can change the starting and stopping of the DC charge.
I do have a latching solenoid to wire in to disconnect the house and starting batteries when the bus is off. This is only going to be an issue during the winter when I'm not getting any sun here in the PNW.

you missed my point.. its not the breaker.. but if you put a meter on the input voltage AT THE DEVICE what do you have.. the mroe current you pull on the feed wires, the more the voltage will drop.. esp true if the wires are too small.. this could trigger the unit to shut down.. then the current pull ceases so the voltage rises back up on the feed and so it turns back on... current goes up voltage drops.. shuts down.. and will do this over and over...

 

[Jono14]

I agree with cadillackid that putting a volt meter on the DCtoDC while it is cycling could give you good info. Looking at the manual page 07 that is between lug 2 and lug 4 - see if you get a pattern of voltages that give a clue as to why it is shutting on and off.

Also, the indicator lights might tell a story as per pages 12 and 17.

The 2 AWG wire itself is not likely the problem. Even if it was a 50 ft round trip, the voltage drop at 50A is not bad at ~3% or 0.4V but if the terminals are dirty or corroded or other parts of the circuit are loose it could become a bigger issue.

If the input voltage checks out, you can also measure the output (lugs 3 and 4) to see that voltage. I am not sure what chemistry your house batteries are but confirm the device matches them and that they are not full. A similar cycling of nearly full batteries could happen if the voltage rises and then settles after the charger shuts off.

I think you are right that Renogy provides no programability - at least nothing is described in the manual, so unless there is a separate control manual it is not clear to me how to change parameters.
Ultimately, the system may require an ignition wire to control the on/off process.

 

[Coloradojeep]

I'll get the volt meter out and do some testing at the terminals. The ignition wire doesn't do anything. I've tried that. It just lowers the starting point of the charge. For my case this would not work because it would continue to charge the house Battery until the starting battery drops below 11.5 volts.

I have 3, 200 ah Lithium Batteries and they are sitting about half full.

 

[Diverdude0075]

Did you have to upgrade the alternator? Could that possibly not be rated for the additional loads?

 

[heimlich]

Do you have lithium batteries? Is the charger set up for lithium? I've heard lithium batteries can put a drain on an alternator.

 

[Coloradojeep]

I'm running the stock alternator so no changes there. I am thinking about going to the one-wire alternator with a tach hookup though.

I do have lithium batteries and the charge controller is set for lithium. I'm not sure why the makeup of the battery would matter as long as it's on the otherwise of a charge controller. I did find on a diy solar forum where other people have had similar problems.

 

[cadillackid]

I'm running the stock alternator so no changes there. I am thinking about going to the one-wire alternator with a tach hookup though.

I do have lithium batteries and the charge controller is set for lithium. I'm not sure why the makeup of the battery would matter as long as it's on the otherwise of a charge controller. I did find on a diy solar forum where other people have had similar problems.

the charge controller should limit the current going toward the lithium batteries.. seems like it should keep the output on even if the auto-off threshold drops when you have the ignition wire fed.. though it may also have an emergency shutdown function as well.. I dont know much about the renogy stuff so I dont know if there is a source battery rundown protection feature triggering or not.. ive used all Victron and theirs do have such functions..

 

[AlphaHare]

I'm running the stock alternator so no changes there. I am thinking about going to the one-wire alternator with a tach hookup though.

I do have lithium batteries and the charge controller is set for lithium. I'm not sure why the makeup of the battery would matter as long as it's on the otherwise of a charge controller. I did find on a diy solar forum where other people have had similar problems.

Maybe it's just the Renology unit itself. Which is cheaper, a new alternator or the charge controller?

 

[Rucker]

I read the description and the device has 'soft start' technology, which means it won't just flip a switch.

If the current draw is greater than 50 amps, it may turn on and slowly ramp until it starts to exceed that rating, then cycle as you described. Is your battery pretty drained? Maybe it's trying to charge at a rate greater than 50 amps and that's causing the cycling...

And why it might explain why it doesn't always trip...

 

[cadillackid]

wierd way for a charger to work... my victron units reach their max and stay there till the battery starts to take less amps... as the battery voltage increases, then the controller alters the charge voltage and method for the state of charge it detects..
never heard of one that turns off and back on constantly.. seems wierd

 

[Rucker]

My NOCO charger does exactly that. I wouldn't have known if I didn't instrument up the thing to check.

But if the soft start is hiding some underlying condition by simply delaying the 'circuit tripping' because it ramps up slowly, that would match the behavior described.