Battery monitors

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Trev
Posts: 160
Joined: Thu Jan 15, 2009 2:56 am
Location: Moruya NSW

Battery monitors

Post by Trev » Sun Nov 03, 2013 4:54 pm

Hi Builders,
I am looking to buy a battery monitoring system to install in my boat, something to tell me the state of charge, amps in, amps out, etc. but I have been told that because I intend to use Lifepo4 batteries that these wont work because of the different "efficiencies" between the battery types? for example they will need to use different formulas to work out state of charge etc. I can see that amps in and amps out would be the same, but what about the rest?
Can anybody tell me if this is true, and if it is, is there such a thing as a battery monitor for Lifepo4 batteries.
Trev

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: Battery monitors

Post by groper » Sun Nov 03, 2013 10:45 pm

The issue with Lifepo4 batteries, is that the voltage change across the middle 70% of the state of charge, is less than 0.1 volts. So typical battery monitors that only use voltage as an indicator, cannot determine the state of charge with any discernible resolution. They can tell if your full or empty, because the voltage curve rolls off sharply at either end, but its almost dead constant throughout the middle and cannot see a difference...

So what can you do?

Well, 1 option, is to use a battery monitor that works via counting the amps in and amps out, and you program into it, the capacity of the battery bank. So in other words, it completely ignores the voltage of the bank and indicates the state of charge by counting the amps out from a preset number - say 400amp hours = full. And once it counts out 200amp/hours it displays 50% for example. So you need a programable monitor.

Im not sure who makes this gear as im still busy building and havnt considered purchases in any detail at this point, but im definately going lifepo4 aswell.

There may be other monitors which can be programed to read very fine voltage resolution specifically for lifepo4 - not sure but seems feasable. Some googling will no doubt turn up more info and theres a long thread with heaps of gold info some 200pages long at cruisersforum.com...

S-berg
Posts: 36
Joined: Tue Nov 23, 2010 3:27 am
Location: Port Denison W.A.

Re: Battery monitors

Post by S-berg » Mon Nov 04, 2013 5:58 am

Hey Trev,
I a using a Victron BMV600 for my battery monitor (LiFePO4 battery). It has the amp counting feature that groper described, as well as numerous other features. I set the Puekerts number to 1.09 from advice off Cruisers forums LiFePO4 post. Thats not quite right, but gives a close representation of the battery state of charge. About $200.
Other brands that i looked at were BEP and NASA and I heard about making your own using a 200mV shunt and the plasmatronics Dingo 2020 solar charge controller as well. I didn't have quite enough electrical confidence to do that.
The Victron was well priced and so easy to install.
Hope that gives you a couple of things to research late at night

Stefan

mahnamahna
Posts: 580
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: Battery monitors

Post by mahnamahna » Mon Nov 04, 2013 10:20 pm

This unit is mentioned in the cruisers forum thread:

http://www.jun-si.com/EnProductShow.asp?ID=96

Its about US$30. But it only reads each cells voltage and not as simple as the one I bought.

I bought this unit on ebay for AU$45 delivered from HK but they seemed to have gone up a little since. Still less than $60, but if you have time, wait until he auctions one rather that buy it now and you can get it for less than $50.

http://www.ebay.com.au/itm/Programmable ... cde&_uhb=1

It is programmable and reads amps, amp hours, volts and can power a relay switch at a preset either high voltage or low voltage (amongst other parameters). With Lifepo4 I would be more concerned about overcharge rather than running them out so I intend to cut out the charge circuit when it reaches top voltage. I may even buy another and set it to say 30amp hours and cut out the power usage circuit if it reaches it, as protection should I ever leave the boat and leave something on that drains the battery.

As for state of charge readings, I will just permanently display amp hours, I know my lifepo4 bank is 400ah so if the reading is 200ah I can do the math.

Trev
Posts: 160
Joined: Thu Jan 15, 2009 2:56 am
Location: Moruya NSW

Re: Battery monitors

Post by Trev » Tue Nov 05, 2013 8:18 am

Thanks guys, I will check out these options and have a look at the cruisers forum also.
Trev

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