solgato avatar image
solgato asked

MPPT 75/15 Switching to Bulk Mode

Aloha. I have a system comprised of (2) MPPT 75/15 controllers in parallel to a 24V bank with a BMV. Each charge controller is fed by (3) 100 watt 20V panels. This system powers dual electric boat trolling motors which are wired directly to the batteries and not to the Load Outputs of the controllers.

My question is, when should the charge controllers switch to Bulk mode? Do they have to see a specific load or a load for an amount of time before switching?

I thought they would switch from Float to Bulk if the voltage of the bank fell below the set threshold, but during mid day sun while both chargers are in Float mode with fully charged batteries, if I turn the motors on and draw a load the chargers do not switch to Bulk to offset the amperage draw which causes the voltage of the bank to drop. I can see this on the BMV. I would have thought a load causing voltage drop below set float value would have caused the controllers to switch to Bulk?

I have tried networking and resetting all devices and double checked all settings.


battery charging
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JohnC avatar image JohnC ♦ commented ·

What's happening to the Amps/Watts from the chargers when you add the load in?

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solgato avatar image
solgato answered ·

Before I installed the BMV when monitoring the controllers using the App, I would see the controllers react to the load and match the amps that were being drawn but they would remain in Float mode according to the lights which I thought was odd.

After I installed the BMV and created a network to which I added the two controllers, sometimes it works as I expected it to when watching the BMV display -turn motors on and the amps and watts go from a negative value to an equal opposite positive value then settle back to zero under steady load. When this happens the voltage of my bank is 25.9V or so and remains steady but the controllers still remain in Float mode while offsetting the motor load. Then sometimes like today I’ll turn the motors on and the amps and watts remain negative and the voltage of the bank drops without the chargers kicking in at all.

I would have thought the controllers would switch from Float to Bulk mode as soon as the BMV reports a significant load or voltage drop.

I’m wondering if there is a specific Amp draw or time required under load before the controllers switch. I’m not running my motors long since they’re not in water and they are only drawing 3A max since they don’t have a load on them.

Checking my history in the app, I see no provision to be able to know what time during the day the controllers are switching between modes, only the duration they remain in each mode. I find it strange that they are going into Bulk and Absorbition mode in the morning I presume when’s there is very little if any sun directly on the panels.

Is it possible perhaps that they can only go into Bulk once a day as part of a charge cycle?

Or maybe the issue has to do with having my motors wired directly to the batteries although the manual states large loads should be. My motors are capable of drawing a max 60A each. Do I need to add a trigger relay of sorts to the load terminals in order for the controllers to switch to Bulk?

Thanks for your response.

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JohnC avatar image
JohnC answered ·

G'Day Sol (that's an Australian Aloha).

I'm not especially qualified to comment on your issues, and your 'wonderings' place you in my logical-thinker basket.

But it may be much simpler than that. If your mppt's work fine without the external influence of the BMV then perhaps it's the BMV? BMV settings that is.

Not coming out of Float suggests to me that a lower target V is being passed on, and subsequently reported. Check your settings on the BMV, and try to follow what's happening with V and A. There should arise some logic to this with deeper analysis.

Sorry I can't help more, this sort of thing is difficult to diagnose remotely without a helluva lot more info.

So just a bump from me. Aloha. :)

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solgato avatar image solgato commented ·

Thanks. I have tried leaving the network and a few other things but the behavior doesn’t seem consistent. I see there are a lot of posts about these controllers not going back into Bulk mode when they are supposed to.

I found another post where a Victron rep stated that the controller needs to see a 1.3V (lead) or .2V (Li) drop to switch into Bulk mode. These are for 12V systems, so 2.6V for 24V lead like mine. This post was about a Multiplus Quattro and not an MPPT 75/15 like I have, but it makes me wonder if there are similar parameters for my charge controller and perhaps I am not forcing them back into Bulk because I’m not running them long enough or drawing enough of a load. This might also explain why they are able to at times maintain the pack voltage and power the motors while remaining in Float mode, because I’m not drawing more power than Float mode is set to deliver to maintain the pack.

I also found posts asking how to force these chargers into Bulk mode and some have been able to trick the charger into a new cycle by covering the panels and removing, and those with the App can switch them off and back on so that they start in Bulk mode.

What I’m wondering is if I need to create a custom preset for my system with settings that keep the controllers is Bulk, a preset specifically for running the motors during the day if you will, then when the boat it at rest a separate preset with settings configured to recharge and maintain the batteries.

Basically I want to be able to use these chargers to provide as much power as they and my solar panels can to offset as much of the load of the trolling motors.

I wish there was a way to upload video, then I could share a screen capture of the systems behavior when it’s working correctly the way I expected it to, and when it is not.

Thanks again for your help!

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solgato avatar image solgato solgato commented ·

I just checked to see if turning the 75/15 charger off via the App forces them back in to starting in Bulk Mode and it does. After restart, running the motor kept it in Bulk, then shortly after turning the motor off it switched to Absorbtion at 31V for a few minutes, then back to Float. This is what I hoped and expected the solar chargers to do automatically, but maybe they are not capable.

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JohnC avatar image JohnC ♦ solgato commented ·

Yeh, you seem to have a pretty good grasp of it all, and your expectations are realistic. I note Matthijs stated just today that a new firmware version is about to enter testing, so if you can wait a little longer, perhaps your issue will be picked up along with those of the others who've reported possibly related troubles.

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