Setting bank Amp hours on Magnum 2812.

[JDCAVE]

I have decreased the house bank size from 1125 AH to 900. The Magnum 2812 was installed in 2015, I believe.

I am trying to change the bank size and cannot determine how to do that on the ME RC 50 Set up panel. I have the following options on my model:

Set up
01 search watts
02 Low battery cut out
03 absorb time
04 battery type
05 charge rate
06 VAC drop out
07 power save
08 screen set up
09 final charge
10 power up always

The paper manual for Setup 03, “Absorb time” has a lengthy discussion on the appropriate setting for Absorb time based on bank size, but there is no provision to change bank size amp hours.

Any advice would be appreciated.

Jim

 

[Bacchus]

I haven't pulled my manual and studied but I think you are looking for the charge rate. Your batty specs should provide a recommended charge rate as a fraction or. % of batty AH. With that and the # battys you should be able to set the charge rate.
IIRC Magnum wants a % of that models max. So if max is 120A and you want 80A you could select 60% or 70% rounding down or up as I think they only accept 10% increments.

 

[JDCAVE]

I haven't pulled my manual and studied but I think you are looking for the charge rate. Your batty specs should provide a recommended charge rate as a fraction or. % of batty AH. With that and the # battys you should be able to set the charge rate.
IIRC Magnum wants a % of that models max. So if max is 120A and you want 80A you could select 60% or 70% rounding down or up as I think they only accept 10% increments.

You know other versions of the manual indicate there is a setting for Amp Hours on “Set Up” but not my paper manual and not on my unit.

I have an email request in to Magnum. I don’t think their technical help is as good as it was in the “old days”.

Jim

 

[Scottwb96]

Do you also have the BMK (Magnum - Battery Monitor Kit)? If not, then I don't believe there is an input for bank size/capacity.

 

[cafesport]

If you added the BMK then it’s menu item 05B other wise NA.

 

[JDCAVE]

Do you also have the BMK (Magnum - Battery Monitor Kit)? If not, then I don't believe there is an input for bank size/capacity.

Yes I do.

 

[JDCAVE]

This is in the manual…


I don’t have this option available to me. Only hours of Absorb charge.

Jim

 

[cafesport]

https://youtu.be/fNgrRhrEbos

 

[O C Diver]

Maximum amperage is only a bulk charging parameter. In the absorption mode, voltage remains constant and amperage decreases over time to maintain voltage.

I believe your Magnum 2812's maximum charging amperage is 125 amps. With the new bank of 900 AH, charging the bank at 125 amps should yield a charge rate of <14%. Even open lead acid batteries (Trojan T-105s) can handle that. My Trojan T-105s when charged by my Leece Neville alternator saw charge rates as high as 20% without shortening their life.

BTW, what is the chemistry (AGM, OA, Lithium, etc) of your new batteries?

Ted

 

[SteveK]

Setup

View attachment ME-RC50.pdf

 

[Scottwb96]

Check and make sure the device (BMK) is connected and has a solid green light. I used to have the same charger/inverter and my BMK would "unplug itself" constantly... Finally had to tape the connection piece so it wouldn't budge...
Then eventually switched it all out for Victron, couldn't be happier! Solid charger, but no interoperability with newer tech really made the decision easy when considering the change. I am now running ~1,400ah LFP ALL Victron/REC ABMS/Wakespeed WS500's (dual setup)...

 

[JDCAVE]

Maximum amperage is only a bulk charging parameter. In the absorption mode, voltage remains constant and amperage decreases over time to maintain voltage.

I believe your Magnum 2812's maximum charging amperage is 125 amps. With the new bank of 900 AH, charging the bank at 125 amps should yield a charge rate of <14%. Even open lead acid batteries (Trojan T-105s) can handle that. My Trojan T-105s when charged by my Leece Neville alternator saw charge rates as high as 20% without shortening their life.

BTW, what is the chemistry (AGM, OA, Lithium, etc) of your new batteries?

Ted

Thanks Ted. I simply replaced the T-105's with "same". I had considered going to LFP but staying with T-105's was the simplest option and I know the technology. I got 9 seasons from my old T-105's with very little decline AH over time. The only change I made was going down from 1125 AH (10 X T-105's) to 900 AH (8 X T-105's). With solar panels, I typically only went down to 90% SOC on the previous bank...

My concern is for the correct calculation of the SOC. If the BMK still "assumes" a bank size of 1125 AH, the SOC will be biased high. I have a request to Magnum but we will see whether they respond.

Jim

 

[JDCAVE]

Setup

View attachment 133195

Ok, I will look at that a little closer. I had thought that "Setup 05" was only for Charge efficiency.

Jim

 

[O C Diver]

Thanks Ted. I simply replaced the T-105's with "same". I had considered going to LFP but staying with T-105's was the simplest option and I know the technology. I got 9 seasons from my old T-105's with very little decline AH over time. The only change I made was going down from 1125 AH (10 X T-105's) to 900 AH (8 X T-105's). With solar panels, I typically only went down to 90% SOC on the previous bank...

My concern is for the correct calculation of the SOC. If the BMK still "assumes" a bank size of 1125 AH, the SOC will be biased high. I have a request to Magnum but we will see whether they respond.

Jim

Jim,

I could be wrong, but the Magnum 2812 doesn't have a shunt, so consumption is estimated by battery voltage. The unit indicates 100% when charging drops below a certain percentage. Battery state of change is measured by average voltage over some period of minutes ( so running the microwave doesn't give you a false low reading). That's how I understand it anyway.

If the battery was charged by solar energy or an alternator, it wouldn't travel through the 2812, so there would be no way for it to know how many KW were put in.

Ted

 

[SteveK]

I have only had 3 inverter brands and none had a shunt. Always a separate item. Is there inverters with built in shunts?

 

[cafesport]

He said he added a BMK, which is a shunt that allows the inverter to calculate amps in vs amps out aka SOC. It can easily be programmed to more accurately measure his new bank size. It’s as good as the victron bmv if you set it up correctly. Unfortunately non of the coulomb counters stay accurate. The only way to truly know if agms or lead acid are fully charged is the amount of current they accept at charged voltage. The video link showed the programming but I guess no one watched it. Carry on.

 

[SteveK]

The video link showed the programming but I guess no one watched it.

Yes, I did, but that was an ME ARC. For some reason there are three controllers for the inverter to choose from and programming may not be the same. OP has ME RC50

 

[cafesport]

So Steve what if I told you the video was a test? It was only provided as a link for magnum owners who wanted to understand the inner workings of their machines. The me rc and me arc are not different enough to cause confusion unless you don’t have one. I’ve answered the question enough times now to get bored of the topic. Since you are the resident expert you can handle the questions from here I’m going back off line.

 

[SteveK]

here is a video for ME RC50. It shows how to change the Ah

 

[JDCAVE]

Thanks all. It will be a couple of days before I can get to this.

Ted. The Magnum BMK kit comes with a shunt.

Jim

 

[JDCAVE]

here is a video for ME RC50. It shows how to change the Ah

Thanks so much, Steve! That got me there! I’ve programmed it in, so I’m good to got. Also, in changing the bank size, I now have changed (shortened) the duration of the Absorb Charge phase.

I found the manual and online resources somewhat opaque on this particular change. I was trying to get there on the setup button, and cycling through it.

Jim

 

[SteveK]