End Absorb : Fixed Time or End Amps?

SandyP

Is there a simple answer to the question : Should you end the battery charging absorb stage using :

1) The end of a fixed Absorb period (ie. 2 hours) or,

2) The charging current (end amps) dropping below a fixed percentage of the battery capacity?

I have seen both of the above discussed however 50% favour a fixed period with the other 50% suggesting end amps is the way to go. Many indicate determining the fixed absorb period by looking at the rate of decrease in amps during the absorb stage and when it stops changing then setting that time for absorb in the charge controller - with the caution that this will change will battery age.

The issue I have is, when the system usage is low (no one home) which could be for many weeks, then the end amps method may see absorb only last for 30 minutes (as would be expected) however is this optimal versus fixing in a +2 hour absorb period (needed when house occupied) irregardless of usage?

If a 2 hour absorb stage will not be detrimental to the battery bank when it only needs a 30 min absorb stage then the fixed period would be best - but is this the case?

NorthGuy

Re: End Absorb : Fixed Time or End Amps?

My understanding is that (1) ensures electrolyte mixing is complete at every absorption even if discharge was shallow, while (2) ensures full charge at every absorption even if discharge was deep.

Since you have gel batteries and do not need electrolyte mixing, (1) is probably not important to you at all and (2) would be a better choice.

Continue absorption when battery is already charged is not good for battery.

ChrisOlson

Re: End Absorb : Fixed Time or End Amps?

The End Amp method is best. However this can be tricky because with a solar charge controller charging a bank at the same time an inverter is drawing power from the bank, an adjustment has to be made to End Amps for the charge controller to know what's going on. MidNite Solar will have a shunt-based system soon for the Classic controller that measures actual amps to the battery and takes into account loading by the inverter that will eliminate all the guesswork with using End Amps to terminate the absorb stage.

I do not know if any other manufacturers have such a thing (I don't think so). So End Amps, until MidNite gets the new shunt-based accessory available, is only really going to work when charging with an inverter-charger.
--
Chris

vtmaps

Re: End Absorb : Fixed Time or End Amps?

ChrisOlson wrote: »

I do not know if any other manufacturers have such a thing (I don't think so).

Outback does end amps with their Flexmax controllers. You must also have their FlexnetDC battery monitor. --vtMaps

boB

Re: End Absorb : Fixed Time or End Amps?

vtmaps wrote: »

Outback does end amps with their Flexmax controllers. You must also have their FlexnetDC battery monitor. --vtMaps

AND a hub and a Mate I think ?

ChrisOlson

Re: End Absorb : Fixed Time or End Amps?

vtmaps wrote: »

Outback does end amps with their Flexmax controllers. You must also have their FlexnetDC battery monitor. --vtMaps

Ah, I had forgot about that. The XW Power System does too, however it's not really adjustable, nor is there a setting for it. You simply enter in the bank's amp-hour size and it will terminate absorb at 2% C even if the timer hasn't expired. But it only works with a XW-MPPT60-150 or XW-MPPT80-600 when hooked on a Xanbus network with a XW inverter. The inverter is the "brains" that knows how much is going to loads and it provides that info to the controllers via Xanbus.
--
Chris

petertearai

Re: End Absorb : Fixed Time or End Amps?

I have the fm80 and my set up is similar to yours. I have my absorb set to 3 hours and absorb end anps to 7 amps. While there on the weekend the absorb will often go the full 3 hours. But if i look at the stats for while away the absob seems to average around 15 min . All good as far as I can see.
I dont have a mate or hub. the end amps and time can be directly put in through the fm80 UI.

SandyP

Re: End Absorb : Fixed Time or End Amps?

Thanks for everyones input on this as it makes me more confident I have things set up correctly.

I was looking at installing a battery monitor system but am torn between a cheap one to just show the SOC using voltage and a proper (but more costly) one like the Outback FN-DC (which would also mean getting a HUB).

bOB's Midnite Solar MNBCM looked OK to ensure visitors (with no RE knowledge) could "see" what the battery status was however it seems it would not correctly show the Battery Care status and may not correctly show the Full Charge occurence if my Absorb stage did not go for >1 hour.

Sun Dog

Re: End Absorb : Fixed Time or End Amps?

ChrisOlson wrote: »

Ah, I had forgot about that. The XW Power System does too, however it's not really adjustable, nor is there a setting for it. You simply enter in the bank's amp-hour size and it will terminate absorb at 2% C even if the timer hasn't expired. But it only works with a XW-MPPT60-150 or XW-MPPT80-600 when hooked on a Xanbus network with a XW inverter. The inverter is the "brains" that knows how much is going to loads and it provides that info to the controllers via Xanbus.
--
Chris

While you can't change the 2% end amps parameter on the XW you can change the input value for you bank size. I used this to get my end amps down to 1% and it happened to work out as the "right" setting based on my battery manufacturer's recommendation for amps during equalization.

ChrisOlson

Re: End Absorb : Fixed Time or End Amps?

Sun Dog wrote: »

While you can't change the 2% end amps parameter on the XW you can change the input value for you bank size. I used this to get my end amps down to 1% and it happened to work out as the "right" setting based on my battery manufacturer's recommendation for amps during equalization.

When we got our XW system I didn't even know that it does that. And they don't explain it, or even mention it, in the manual (at least not that I've found).
--
Chris

unicornio

Re: End Absorb : Fixed Time or End Amps?

absorption phase ends with the "amp of return" system is the best to ensure a dynamic way to get easily a optimal charge and care of the battery ...

outback does that perfectly, consisting of one of the most complete and accurate systems that currently exist in the control of the battery status and control, and even you have to buy the hub, the mate (better MATE3), and flexnet DC and the three shunts , the advance to have these devices goes beyond because is the way to complete the control of the outback whole system ...

petertearai

Re: End Absorb : Fixed Time or End Amps?

Consider the victron moniter . easy to install , and simple for guests to understand.

SandyP

Re: End Absorb : Fixed Time or End Amps?

petertearai wrote: »

Consider the victron moniter . easy to install , and simple for guests to understand.

Thanks for the suggestion - the Victron BMV 600S looks like a good unit to display some general battery information.

unicornio

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

Thanks for the suggestion - the Victron BMV 600S looks like a good unit to display some general battery information.

yep!...but if your equipment is outback, th FlexNet DC can manage and sync all your charge controllers too!...

SandyP

Re: End Absorb : Fixed Time or End Amps?

unicornio wrote: »

yep!...but if your equipment is outback, th FlexNet DC can manage and sync all your charge controllers too!...

Thanks Unicornio however, I think the Victron will do nicely as all I am after is some simple display information and some records of battery charging / use. Yes, the FN-DC has a wider use but most I do not need with the simple system I have.

I purchased the Victron today ($199 here in Aus) and will install when I get the chance to get to the house (probably in June).

Happy to see that the Peukert’s exponent for my batteries is only 1.15.

unicornio

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

Thanks Unicornio however, I think the Victron will do nicely as all I am after is some simple display information and some records of battery charging / use. Yes, the FN-DC has a wider use but most I do not need with the simple system I have.

I purchased the Victron today ($199 here in Aus) and will install when I get the chance to get to the house (probably in June).

Happy to see that the Peukert’s exponent for my batteries is only 1.15.

i think that the victron have a relay contact that allow you to put the genset to charge, and maybe you can use this relay to stop absorb charge step when really the end amperes are reached...(you can use the outback auxiliary contacts from vfx or flexmax to manage the genset too)

SandyP

Re: End Absorb : Fixed Time or End Amps?

unicornio wrote: »

i think that the victron have a relay contact that allow you to put the genset to charge, and maybe you can use this relay to stop absorb charge step when really the end amperes are reached...(you can use the outback auxiliary contacts from vfx or flexmax to manage the genset too)

Thanks Unicornio, I currently use the end amps on the FM60 to stop the Absorb stage.

A couple of questions for the forum :

1) Does it matter where you put the shunt for the Victron BMV on the -ve battery-load lead? Close to the battery or close to the inverter?

2) I have 70mm2 cables and not sure how hard it is to 'adapt' these to install the shunt? Or should I just purchase a short pre made battery interconnect lead?

EDIT : Also after installing the shunt should the battery lead lengths (+ve & -ve) be the same?

Thanks.

newl

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

I purchased the Victron today ($199 here in Aus) and will install when I get the chance to get to the house (probably in June).

Where from? For that price I'd grab one.

unicornio

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

Thanks Unicornio, I currently use the end amps on the FM60 to stop the Absorb stage.

the FM60 can not know if there is any power consumption, so you can not do that function unless all loads are disconnected at this time ...

SandyP wrote: »

A couple of questions for the forum :

1) Does it matter where you put the shunt for the Victron BMV on the -ve battery-load lead? Close to the battery or close to the inverter?

the shunt: you can place it anywhere you like as long as it is connected directly to the terminal of the battery ...

SandyP wrote: »

2) Also after installing the shunt should the battery lead lengths (+ve & -ve) be the same?

the difference between the length of two serial cable is indifferent ...

petertearai

Re: End Absorb : Fixed Time or End Amps?

Yep the fm80 can not make adjustments to end amps when loads are present, but in my holiday home situation it works well because the absorb is stopped only after 15 or so minutes while im not there,

SandyP

Re: End Absorb : Fixed Time or End Amps?

newl wrote: »

Where from? For that price I'd grab one.

Try these guys in Queensland : http://www.marineequip.com.au/victron-battery-monitors.html

SandyP

Re: End Absorb : Fixed Time or End Amps?

unicornio wrote: »

the difference between the length of two serial cable is indifferent ...

I emailed my installer who indicated, where ever possible, the cables should be the same length and also advised that I follow the battery manufacturers advised bolt tension on the terminals (around 8 N/Mt from memory).

vtmaps

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

EDIT : Also after installing the shunt should the battery lead lengths (+ve & -ve) be the same?

unicornio wrote:

the difference between the length of two serial cable is indifferent ...

SandyP wrote:

I emailed my installer who indicated, where ever possible, the cables should be the same length

I agree with unicornio. In a series battery bank, none of the cables need to match. Of course, they should all be as short as possible.

In a parallel bank, once the parallel strings are joined, the cables that run from the 'joining point' to the inverter can also be of different length.

Example: Suppose that you need a 4 ft cable to reach from the battery negative to your inverter, but you need a 5 ft cable to reach from battery positive to the inverter. There is no good reason to use two 5 ft cables when a 4 ft and a 5 ft will do.

One more thing... you do not need to attach the shunt directly to the battery negative. You can run a cable from your battery negative to an electrical box where the shunt is located. From the other side of the shunt you continue to battery negative bus bar. From the negative bus bar you connect (through fuses or circuit breakers) the controller and inverter. If you are bonding your battery negative to ground (through a GFP or not) make sure the bond is on the side of the shunt that is not connected to the battery. EVERY connection to battery negative must go through the shunt.

--vtMaps

NorthGuy

Re: End Absorb : Fixed Time or End Amps?

vtmaps wrote: »

One more thing... you do not need to attach the shunt directly to the battery negative. You can run a cable from your battery negative to an electrical box where the shunt is located. From the other side of the shunt you continue to battery negative bus bar. From the negative bus bar you connect (through fuses or circuit breakers) the controller and inverter. If you are bonding your battery negative to ground (through a GFP or not) make sure the bond is on the side of the shunt that is not connected to the battery. EVERY connection to battery negative must go through the shunt.

And you can use shunt as a bus. I have two solar controllers connected to one side of the shunt. If I had the shunt elsewhere, I would have to use something else to connect them both to the battery.

SandyP

Re: End Absorb : Fixed Time or End Amps?

vtmaps wrote: »

I
One more thing... you do not need to attach the shunt directly to the battery negative. .......... EVERY connection to battery negative must go through the shunt.
--vtMaps

I planned to insert the shunt into the -ve lead close to the battery isolation panel as this is where the leads from the FM60 are "attached" and input the power to the batteries.

The Victron BMV-600s arrived today - the 500mA shunts are bigger/heavier than I expected! Also had a concern as I could not get the small +ve power supply wire inserted into the circuit board on the shunt-seems it was a Friday model and some of the glue had jammed the orange catch that, when pressed, allowed the wire to be inserted. All good now - just have to get to the house!

SandyP

Re: End Absorb : Fixed Time or End Amps?

Today had the Victron shunt / meter installed into the -ve 70mm2 battery lead :

Attachment not found.

unicornio

Re: End Absorb : Fixed Time or End Amps?

in relation to the title of the thread, as you plan to do for the absorption stage ends with the "end amps" parameter with this battery monitor? ...
if it has nothing to do with the title of the thread, i have nothing to say ... ;-)

SandyP

Re: End Absorb : Fixed Time or End Amps?

The victron will allow viewing of the actual amps going into the battery versus the amp output shown on the FM60 which is "shared" with background house loads as well as charging the batteries.

YehoshuaAgapao

Re: End Absorb : Fixed Time or End Amps?

ChrisOlson wrote: »

The End Amp method is best. However this can be tricky because with a solar charge controller charging a bank at the same time an inverter is drawing power from the bank, an adjustment has to be made to End Amps for the charge controller to know what's going on. MidNite Solar will have a shunt-based system soon for the Classic controller that measures actual amps to the battery and takes into account loading by the inverter that will eliminate all the guesswork with using End Amps to terminate the absorb stage.

I do not know if any other manufacturers have such a thing (I don't think so). So End Amps, until MidNite gets the new shunt-based accessory available, is only really going to work when charging with an inverter-charger.
--
Chris

Xantrex uses network communication to have the inverter communicate its amp draw to the charge controllers. The inverter's amp measurements are not very accurate so I can never get extended absorb times while selling to the grid. Selling to the grid is a much higher load than just powering the loads. Enhanced interactive mode is definitely necessary if you want any kind of proper absorption charge while grid-selling. I like the idea of having a networked-connected shunt-based measuring device. Unfortunately, XANBUS is proprietary. Midnite Solar's device will probably speak MODBUS.

unicornio

Re: End Absorb : Fixed Time or End Amps?

SandyP wrote: »

The victron will allow viewing of the actual amps going into the battery versus the amp output shown on the FM60 which is "shared" with background house loads as well as charging the batteries.

yeah!...but who will see this?...maybe you, but obviously, your outback equipment can't see the data of this battery monitor...

SandyP

Re: End Absorb : Fixed Time or End Amps?

unicornio wrote: »

yeah!...but who will see this?...maybe you, but obviously, your outback equipment can't see the data of this battery monitor...

No, the Outback FM60 cannot see this however, it will assist me in manually setting the absorb end amps based on average background loads during charging.