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Timx

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Spurred on from another thread, I have 3x 230 ah batteries, my bmv tells me they are 100pc when the tale current is about 25, so I ignore that and keep charging when running the engine to under 1pc , it gets to about 5 something, 

i do this weekly whilst running the engine, easy at the moment through summer. Even then I spoil myself and plod into a marine to give it a good charge every couple of weeks.or a pub with eleccy hook.in winter I visit a marina more often just for a night, or if forced to by a freeze coming, but basically the same thing, give the batts a good charge.

So everything is fine, (I only know what I know from reading on here)

i have two solar panels , think there 100 w

when I leave the marina etc and bmv is reading around 0 amps, as soon as I put it on inverter it jumps to , tail current 4v.

When it's a sunny day and I haven't ran the engine, it can show being 100pc when, if I start the engine the tail current would show about 70,amps, that's against running the engine till it gets to 100 pc then it's 25a,

why is there a discrepancy between the two figures?

i do charge to as far as I can , regularly and have no prob with batteries, I probably protect them too much, but why do I get two different readings as 100 pc, both wrong I know, just wondering.?

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You’re best off completely ignoring the BMV SoC reading. The simplest way of determining 99.9% charged is when the charge current has dropped to <6A at 14.4V charging voltage (or above). Don’t be fooled into thinking the tail current is nice and low if the charging voltage is also low, as can happen if a charge source switches to float. 

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8 hours ago, Timx said:

...I have 3x 230 ah batteries, my bmv tells me they are 100pc when the tale current is about 25, so I ignore that and keep charging when running the engine to under 1pc , it gets to about 5 something,...

 

I agree with WotEver, and always use tail current (and I monitor the rising voltage, although I've never had that try to fool me) to tell me my battery state when charging.  

 

However, you do know that you can alter the settings in your BMV, don't you?  I think the default tail current is 4%, but whatever it is you could change it to the 1% you quote. Similarly, you can set the battery capacity which, with a 25a tail current when it declares 100% I'd guess you have, but if you're using 3 x 230 = 690 its probably too high as battery capacity drops with use/age. Trouble is, you need to guess what it is and this is a key factor in why these meters can't be relied upon to get the 100% anything like right when charging (even if the charging algorithm worked perfectly, it usually underestimates where the finishing line is).  So, whilst you can't depend on the % SoC figure, particularly when charging, you can help to make your BMV"s guess a bit less wrong! 

 

When my batteries are not charging, I leave the BMV set to volts - a search on Google will turn up 12v battery SoC tables which help to interpret battery state from resting voltage. When you don't have a resting voltage though (because you're discharging) there's always the amp hours used read out and the properly set up SoC ‰ will now at least give you a better guess when discharging.  It's here where I see some use for the % SoC readout, and that is as a rough guide for others in your crew who can't be expected to grasp the above.

 

Look on the bright side Tim: at least you have a gauge, and you're using it without letting it hoodwink you!  Many, possibly most, folks have no meter and/or no idea of whether they are charging their batteries correctly.

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As per what sea dog said. I'd go along with that. If you use the factory settings for the parameters, our BMV changes to 100% with a tail  current of 25A .......we also have a capacity of 660 ish Ahrs. If you change the parameters then you can get it to behave better BUT it is a complete waste of time. I NEVER look at the SoC. As sea dog says, just keep an eye on voltage and Amps.

There was a post on here about six months ago which gave the best parameters for the BMV but I did a search and can't find it. I can look at mine as I used the recommended settings but it will have to be later today. Sure someone will pipe up with the best settings.

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