ProNautic 1240P won’t exceed 11.7 A of charge

[toomanyirons]

ProNautic does not exceed 11.7 A

I have a ProMariner ProNautic 1240P charger (rated for up to 40 A, on a 30 A shore power circuit, run through a 20 A breaker before power hits the charger). It charges a house bank of two Victron SuperCycle AGMs (170 Ah ea, 340 Ah total) and a Blue Sea Systems ACR parallels the Odyssey Extreme (103 Ah) AGM starting battery when charging voltage is detected.

I set the custom charging profile in the ProNautic to 14.6 V in “Charge/Condition” mode and 13.6 V in “Auto Maintain” mode. I used the Victron data sheet voltage numbers for Absorption (14.2–14.6 V) and the Odyssey cutsheet numbers for “Charger voltage” (14.4–14.8 V) but there is some confusion in terms here… I’m assuming the ProNautic’s Charger/Conditioning mode roughly corresponds to Absorption voltage? (I’ve also used the AGM profile 2, which has the same voltage numbers and suggests that my custom settings are right).

In the four years I’ve owned the boat and charger (the batteries are two years old), I’ve never seen the current on the charger exceed 11.7 A, despite its 40 A rating, including today when I was charging a battery at “0% state of charge” after returning to the dock because my alternator failed to charge the batteries. Only one or two of the six charge percentage lights ever illuminate.

Even at a conservative 80% of the shore power terminal’s 30 A, the charger should be able to put out 24 amps, which might blow the breaker on the boat, but I don’t understand what’s limiting the output to less than 12 A. (I installed the 20 A breaker alongside a 30 A breaker for the rest of the house loads on an electrician’s advice two years ago, but I don’t remember why the charger breaker is 20 A.)

Why is the ProNautic limited to 11.7 A of charging current? I’m worried that chronic undercharging will shorten the lifespan of the AGMs.

 

[Don S/V ILLusion]

It will help to also know at what voltage you see this max. charge current

 

[dlochner]

The ProNautic has output for 3 batteries, how many outputs are you using? Are the AGMs wired in parallel or independent?

Battery chargers with more than one output divide the output between the terminals. Thus, a 40a charger connected to 2 batteries will only supply 20a to each battery. If you are charging each battery independently, then that could account for the reduced amps being shown.

AGM batteries are Lead Acid batteries. All LA batteries will limit the amount of current that can be accepted based on the batteries SOC. As the SOC increases, the voltage from the charger should rise and the amperage decline. What voltage are you seeing when the charger is 11a?

If you have the remote monitor for the charger, it is easy to see what the charger is doing. When first turned on, the ProNautic puts out 100% of its capacity until the programed output voltage is reached at which point it holds the voltage steady and decreases the output amps until it reaches a very small amp output, at which point it switches to a float voltage.

The smaller breaker is likely due to wire size feeding the charger. While the charger is capable of putting out 40a it does not consume 40a of AC. When comparing differing voltages it is better to use watts. At 12v 40a is equal to 480w, that 480w is roughly equal to 4 amps at 120v. (This is not an exact comparison, power in AC has some other factors, this analysis is close enough).

 

[toomanyirons]

It will help to also know at what voltage you see this max. charge current

13.0 V.

(I updated the original post).

 

[toomanyirons]

The ProNautic has output for 3 batteries, how many outputs are you using? Are the AGMs wired in parallel or independent?

Battery chargers with more than one output divide the output between the terminals. Thus, a 40a charger connected to 2 batteries will only supply 20a to each battery. If you are charging each battery independently, then that could account for the reduced amps being shown.

I’m only using one output to charge the house bank (2x 170Ah AGMs in parallel). The ACR combines the house bank with the cranking battery to top it off.

I didn’t think to look at the voltage yesterday, but it has been steady at 13.0 V, well below both my voltage settings (14.6, 13.6) all morning, with the amps consistently around 11.3–11.7 A. This is consistent with pretty much every time the batteries have been discharged to any significant extent.

 

[Davidasailor26]

When 340 AH of AGM are deeply discharged they should be able to take the full amount of current the charger can provide, in bulk mode, so that’s not what limiting you. As dlochner said the AC side amperage isn’t either.

Are you getting the 13V reading at the charger or at the batteries? What is the wire gauge of the cables between charger and battery, and how long are they?

The possibilities I can think of, in order of decreasing likelihood, are:

• You have a bad connection between the charger and the batteries, or a cable that’s much too small causing significant voltage loss in that part of the circuit. That would cause the charger to think it was done charging the batteries or letting it go into an absorption mode rather than bulk. If that’s the case I’d expect to see a voltage on the charger end much more than at the battery end.
• The charger isn’t really configured with the proper bulk, absorption, and float voltages that you think you’ve set
• There are excessive loads on the batteries so 30A is going off to feed the loads rather than charging. It seems unlikely that you have that much constant load though, and if you did I think the charger would show a high load on its display

 

[dlochner]

Even at a conservative 80% of the shore power terminal’s 30 A, the charger should be able to put out 24 amps, which might blow the breaker on the boat, but I don’t understand what’s limiting the output to less than 12 A. (I installed the 20 A breaker alongside a 30 A breaker for the rest of the house loads on an electrician’s advice two years ago, but I don’t remember why the charger breaker is 20 A.)

The breaker doesn't limit the output of the charger. According to the manual, a 15a AC breaker is recommended for the 1240.

There is a Power Level Adjustment. Did you change this? If you did, put it back to 100%.

Do you have temp sensor on the battery?

 

[toomanyirons]

There is a Power Level Adjustment. Did you change this? If you did, put it back to 100%.

Do you have temp sensor on the battery?

The power level had been set to 25% - that fixed it. I've gone through the manual a couple times but hadn't noticed that part recently. The charger is now reading 13.9 V and 40-41 A, which is a little nerve racking at first but hasn't blown any fuses or tripped any CBs yet. Frustrating to realize such a simple thing might have shortened the life of the expensive AGMs I decided to spring for two years ago, but it's a relief and very satisfying to fix that. (As my dad would say, RTFM!)

There is no temp sensor currently installed. The manual says it comes standard, but I will have to order one.

The charging cable is 6 AWG and 6.5-ft long.

Now that the charging voltage has risen to 14.0 V (and climbing) the voltage at the house bank reads 13.69 V. That drop seems like a bit much, but I've got other fish to fry and I'm stoked to fix this problem.

Thanks again to everyone who replied, I'm working under time pressure and this has been a huge help.

 

[dlochner]

Glad we can help out. I have a 1250, the manual is the same, so I did RTFM.