Current limiting, in general.

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fallguy1000 asked Jun 20, '22

Current limiting, in general.

Running Multiplus 2000/24, MPPT 100/50 with 640w solar, cerbo with no screen, and two Orion 12/24/15 off two outboards with 33amp 12v alternators. Battery bank is two gr27 agm gel, with space for two more.

Concerned about too much current flowing to my too small bank. I can size the bank up, but want to understand how to current limit.

The Orions can deliver 30amps total, solar, say 22 amps, and if hooked to shore power, the Multiplus charger some other higher amount like to 50 amp. So, seeing this as up to 102 amps into two batteries sounds like a fire or exploding battery.

I don't even know how to determine the safe charging limits, so any help is appreciated.

Multiplus-II cerbo gx charge current limit

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Answer 1 · 2022-06-20T15:42:51Z

fallguy1000 answered · Jun 20, 2022 at 03:42 PM

I am also running BMS 712

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Answer 2 · 2022-06-20T16:10:22Z

Alexandra answered · Jun 20, 2022 at 04:10 PM

@fallguy1000

You can use DVCC to control the system wide current that is the mppts and multiplus charging the system.

But the Orions cannot be controlled by the Cerbo.

Are your battteries rated at C10? If so then it is their capacity divided by 10 that is roughly what you want to charge/discharge at.

What does the manufacturer specifications actually say though. That should give you good direction there.

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Answer 3 · 2022-06-20T17:33:23Z

fallguy1000 answered · Jun 20, 2022 at 05:33 PM

East Penn says max charge rate is 30% of Ahr rating. AHr rating is 92 per battery, but system is just 24v, so still 92Ahr at 24v. So, max amperage is 27 which means even the Multiplus has been overcharging. I need to do some homework on the cerbo. I printed the manual and gonna go reset cerbo.

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Answer 4 · 2022-06-20T17:58:17Z

fallguy1000 answered · Jun 20, 2022 at 05:58 PM

How do I deal with the Orions? Typically, the Multiplus would be off when the Orions are, so really when they are on; need to limit the solar..

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Answer 5 · 2022-06-20T18:25:29Z

kevgermany answered · Jun 20, 2022 at 06:25 PM

Max charge rate is max, and for agm that max is high, will shorten battery life. You need to balance charge rate with time available to charge. The C10 rate @Alexandra quoted is a normal balance between charging quickly and shortening battery life. (C10 means 1/10th of battery capacity, 9.2A here, not the 30A from 1/3 capacity)

There's no charge rate setting on the Orions, they're voltage based. There is another potential problem here. The Orions will take pretty much full power from your alternators, which can lead to overheating/burning out the alternators. If you never let the batteries get low, possibly OK, but...

Your system is very low on battery capacity. Suggest you rewire the orions to be switched manually, not automatically, and then only use for short periods. And set up dvcc in the multi as suggested, with a max charge current of 9A. This will control the mppt, if the two are connected with a VE direct cable. You may have to increase this current if you have heavy loads when on shore power.

Background, all the chargers use a 3 stage charging system, stage 1 is max current, during this battery voltage increases, until it gets to the absorption setting, then during the second stage, absorption, voltage is maintained and the current drops as the batteries become charged. Batteries control the charge rate. Once this has gone long enough, chargers switch to float. Keep batteries charged. So as voltage rises under charging conditions, the batteries limit the charge rate. Unless you run your batteries low, the amount of over current won't be as bad as you're thinking.

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fallguy1000 commented · Jun 20, 2022 at 11:18 PM

So, I think I'll add two more batteries. Set the dvcc. I think the output of the Orions is limited to 15amps with a 20amp burst, so despite the fact the alternators are 33-35amp; the maximum output of the Orions is 15amps at 24v, ugh... walked into it but sounds like I could pull 30 amps at 12v from the alternators...I did raise the start voltage, but once they are open; they'd probably be able to take a lot..the alternators are surely internal regulated, so not sure how I can make them work differently.

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fallguy1000 fallguy1000 commented · Jun 20, 2022 at 11:19 PM

Of course, my batteries get low easily because the bank is small, so maybe I have to add to it..

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kevgermany ♦♦ fallguy1000 commented · Jun 21, 2022 at 04:54 AM

30A at 12V is probably fry the alternator territory if it's sustained.

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Answer 6 · 2022-06-20T18:27:13Z

fallguy1000 answered · Jun 20, 2022 at 06:27 PM

I suppose one solution would be to rightsize the battery bank and add another pair of batteries. Then the system would handle a theoretical 54amps which would be within the Orions and Solar maximums.

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kevgermany ♦♦ commented · Jun 20, 2022 at 08:02 PM

Still charging very fast, and doesn't give any relief to your alternators.

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fallguy1000 kevgermany ♦♦ commented · Jun 21, 2022 at 02:15 PM

So, this business of the wire limiting the current.. The wire from the start battery to the Orion is about 1' long. The wire going from the Orion to the house battery is about 16' long on one side and about 18-19' long on the other side. It is 8 gauge. The common wire is shared by both engines and so heavier 2 gauge. How would that affect the alternator output. It is for a boat and sized appropriately at 8 gauge. The shorter wire before the Orion is the same gauge, but probably could be made into a smaller gauge wire, but would it heat?

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Alexandra ♦ fallguy1000 commented · Jun 22, 2022 at 12:24 AM

Undersized cabling will always overheat and using cable to current limit is not what i would consider a safe idea.

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fallguy1000 Alexandra ♦ commented · Jun 22, 2022 at 07:32 PM

Yeah. Alexandra, can you tell me what happens precisely after the bulk timer runs for say 30 seconds? Does the system start over and reference the start cycle or does it only use the absorption voltage and kick back in instantly? That is, could I set the start cycle at say 3 minutes and charge for 30 seconds? This would keep the alternator from frying or me playing with the enable like a toggle on deep discharge of my house..

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Answer 7 · 2022-06-21T15:59:50Z

fallguy1000 answered · Jun 21, 2022 at 03:59 PM

Couldn't Victron fix this with a simple step of cycling the Orion? For example, the Orion could produce current for say 60 seconds and then be off for 2 minutes. So the bulk time would be 60 seconds and then the charging would not start for a time? It already has a delayed start timer for charging the start battery. Seems like using a timer would make it so their Orion devices would be less likely to fry stuff.

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kevgermany ♦♦ commented · Jun 22, 2022 at 08:33 PM

Let's concentrate on what is in today.

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Answer 8 · 2022-06-21T16:06:49Z

fallguy1000 answered · Jun 21, 2022 at 04:06 PM

...versus starting back up based on low voltage as is now

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kevgermany ♦♦ commented · Jun 21, 2022 at 05:14 PM

Yes, but total power draw will be the same and more batteries means less resistance than 2

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fallguy1000 kevgermany ♦♦ commented · Jun 21, 2022 at 09:47 PM

But if my bank is 182Ah, 10% is 18.2A, and each Orion is 15A, so I could theoretically run one engine as the charger. Then as long as it cycled, no worries about frying the alternator. Do you know if I set the bulk charge time limit to 30 seconds if the Orion goes back to the starter battery charge timer or would kick back in immediately based on the absorption voltage threshold?

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Answer 9 · 2022-06-21T21:59:33Z

Charlie Johnson answered · Jun 21, 2022 at 09:59 PM

With your current setup how much charging current does your AGM bank receive from the Orions when the bank is depleted?

I ask this because lead acid batteries (AGM, FLA and GEL) all have a definite charge acceptance rate (CAR). Batteries are rated many ways but the most convenient and familiar is the 20 hour rate designated C20. A battery with a C20 = 100Ahr when subjected to a load of 100Ahr/20A = 5A will reach termination voltage (10.7VDC) in 20 hours. The CAR for LA batteries is between 0.15C and 0.20C (plus or minus). You don't have an overcharging problem caused by too much charging current.

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kevgermany ♦♦ commented · Jun 22, 2022 at 08:42 PM

This is two 92Ah batteries in series for 24V. With two 15A chargers, that is roughly 30A at 24V into a 92Ah bank. I.e. C3 charge rate. And there's the alternator overload issue. We generally work on C10. Charging faster is quite possible, at the expense of battery life. Alexandra and I explained all this above.

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Answer 10 · 2022-06-22T19:36:01Z

fallguy1000 answered · Jun 22, 2022 at 07:36 PM

I am going to go get two more batteries and get to 182 Ah, so 10% would be 18.2A. I would never run both 12/24-15 Orions, so one would deliver the 15 amps and keep the bank safe. The problem is if the bank is depleted, I would be pulling 30 amps from a 33-35amp alternator for too long and probably cook them. The Orion needs to cycle or I have to spend money on a Buck Boost.

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kevgermany ♦♦ commented · Jun 22, 2022 at 08:26 PM

Sounds good if the single Orion input is coming from both alternators at once. But I don't see any benefit in a buck boost.

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fallguy1000 kevgermany ♦♦ commented · Jul 12, 2022 at 12:50 PM

Won't buck boost allow me to configure the maximum current flow from the alternators?

I apologize. I did not see the last comment until now. Assumed you had all gotten tired of me. But I need to resolve this issue still.

I am adding to the bank. Going to set dvcc to 10% of the bank AH rating.

I have been on houseboats that all charge the house with the ouboard engines; generally smaller ones even. How do they avoid cooking alternators? The only difference is voltage is probably 12 on the house.

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kevgermany ♦♦ fallguy1000 commented · Jul 13, 2022 at 03:18 AM

I didn't think about current control, good point.

Not sure what the houseboats do.

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dc4me commented · Jul 13, 2022 at 04:01 AM

One thing you might keep in mind is running alternators at heavy loads you will never get rated output as temperature increases. I think kevgermany is spot on "The Orions will take pretty much full power from your alternators, which can lead to overheating/burning out the alternators." I would be curious to know when the alternators get hot if they would have enough output to power the orions you have.

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