130ah battery bank, only 2-3 hrs at 500w?

[Steve Fractals]

Not yet had a reply from MPP but only been a day.

After lots more reading, I don't think this is an inverter issue but I still could be wrong. It appears that the charger in my inverter uses both voltage and resistance to monitor whilst charging. So this should/could mean that bulk charging also includes absorption.

I watched it today and can see that it pumps charge in at a decent rate of 9.6 amps (max set to 10a) and continues at that rate even when bulk charge set rate has been reached. It continues at this 9.6 rate until the batteries get to about 34ah's stored. It then slowly ramps down but still charging at 3.6amps current until the 36ah ish mark. Then it seems to keep slowly dropping the current until it goes below 1 amp.

At the same time the battery monitor shows various Int Resistance numbers with it showing at around 186m ohm whilst still pumping in at around 3.5-6 amps. Then when it gets to 36ah's stored on the monitor it ramps down again to under 1amp current with resistance jumping between 117m ohm and 300+m ohms and then just sits pumping between .3 and .6 amps current with the resistance fluctuating. I have also seen the Int resistance display on the monitor drop to 0 m ohms a few times which I'm guessing means open circuit and will not accept any charge which would to me at least indicate the batteries are full.

With this pattern, I'm now back to wondering if I've been sold batteries with a fake capacity rating being more like 35ah instead of the quoted 130ah. I guess I really need to break the pack and test individually with a 12v charger. Means I'll have to borrow or buy one as don't own one but hey ho.

Thought's anyone?

 

[Zwy]

Charge them up with a regular battery charger and test them. You have a shunt and I gave you the discharge rate in this post. https://diysolarforum.com/threads/130ah-battery-bank-only-2-3-hrs-at-500w.54651/post-701778

What is the individual battery voltage reading when you think the batteries are full?

 

[Steve Fractals]

Charge them up with a regular battery charger and test them. You have a shunt and I gave you the discharge rate in this post. https://diysolarforum.com/threads/130ah-battery-bank-only-2-3-hrs-at-500w.54651/post-701778

What is the individual battery voltage reading when you think the batteries are full?

Thanks again,

They are reading around the 13.8 mark straight off full charge and the 13.6 mark after 24 hours of being off charge. I'm picking up a regular 12v charger off my bro again tonight so will break the pack over the weekend and fully discharge and re-charge etc with shunt connected and the discharge rate as you suggested.

I'll come back and update after that.

 

[Steve Fractals]

So tried 3 12v chargers so far but still going.

Tried 2 smart chargers (one reports up to 120ah supported) and they seem to both slow right down once the battery hits the 30+ah stage (like my inverter) and charge rate drops to around 0.30A which I assume is either float mode or something e.g. battery is resisting charge.

The third charger I'm currently trying may be described as a dumb charger. With this one it again slows/ramps down at the 30+ ah mark but rather than dropping to 0.30A, this one drops to 2A rate until the battery hits around 35ah and then this drops to a charge rate of 1ah but is still ticking away.

Surely the chargers should be charging at a higher rate until around 80% of battery is charged before ramping down but not sure how they determine this 80% mark. Is it battery voltage or the internal battery resistance etc?

My shunt monitor is reporting that the battery is hitting 600 m ohms once the battery gets over this 30+ ah mark but bounced around. I'm guessing these are high numbers and it's the battery resisting the charge but is that the case and does this resistance indicate that there is something wrong with the batteries etc?

I'm letting this dumb charger carry in at 1A rate just to see if the shunt will report anything like the 130ah alclaimed battery capacity claim. At this snail like 1Anrate of course that's going to take days, surely the battery should easily accept a higher charging rate until it reaches around 100+Ah before dropping to snail rates?

 

[Zwy]

It appears the batteries are fully charged. Install the shunt and you need a constant load on the inverter or use a load that is constant. The 12V 400W heater isn't ideal because the amp draw is too high. You need something along the lines of 6.5 amps. A few headlight bulbs for example. For small loads, I just use an old 350W inverter with a 150W incandescent light bulb plugged in and use a dimmer switch to control the amperage.

 

[Steve Fractals]

It appears the batteries are fully charged. Install the shunt and you need a constant load on the inverter or use a load that is constant. The 12V 400W heater isn't ideal because the amp draw is too high. You need something along the lines of 6.5 amps. A few headlight bulbs for example. For small loads, I just use an old 350W inverter with a 150W incandescent light bulb plugged in and use a dimmer switch to control the amperage.

They do discharge the ah's that the monitor says they've got but charging past 32ah's slows right down to 1amp or less with all chargers I've tried so no good to me when it will take them upto 4 days to reach full charge of 130ish ah as all charges past 30% are at this trickle rate. With this in mind, I am returning them as clearly starter batteries but sold as deep cycle.

I've just now ordered a LifePo4 and sod the money lol.

 

[Zwy]

They do discharge the ah's that the monitor says they've got but charging past 32ah's slows right down to 1amp or less with all chargers I've tried so no good to me when it will take them upto 4 days to reach full charge of 130ish ah as all charges past 30% are at this trickle rate. With this in mind, I am returning them as clearly starter batteries but sold as deep cycle.

I've just now ordered a LifePo4 and sod the money lol.

It almost appears the batteries are severely sulfated.

You will be much happier with LFP.

 

[Vigo]

Wow, i'd really love to know what was happening here.

So from what i know, most chargers that do not have a setting for absorption timer, use a 'rate of change' method to determine when to switch to float. Basically, when the battery is lower SoC and accepts charge more readily, it will 'clamp' the charging circuit voltage to be just a bit above its own 'resting' voltage, a few tenths in most cases. But, as the battery nears ~80% SoC or so, its internal resistance rises and it no longer 'clamps' the charging circuit down to its own voltage to the same extent. In other words if you hook a 16v charger to a drained 12v battery it will hold it far below 16v, but as that battery charges there will come a point where the voltage will quickly rise to something much closer to 16, which is abusive to the battery even if it's not fully charged. A battery only wants to have current flown through it at a certain rate per certain set of conditions, if you exceed that it's unhappy. This is the point where we have to transition to float. So charger watches voltage rise vs time and if voltage rises 'a lot' in a 'short' time it switches to float.

The way around this, sort of, is using equalization settings. During equalization it will use YOUR timer instead of its built in 'voltage rise vs time' regime and act like a fixed source until the EQ timer runs out, or you manually stop it.

So that would be something to try if you wanted to experiment with it. But given that the batteries have done something very similar on multiple generic 'lead acid' chargers, Zwy is probably right that the internal resistance is far higher than 'generic global lead acid average' the chargers are programmed by, and while the limited settings of the chargers are making the diagnosis more difficult, it's ultimately probably 'bad batteries' in the end.

Now, if they are already bad they can't get much worse, so if you want to do something like experiment with just using EQ settings to bypass the internal bulk-to-float switchpoints, it may make them more usable for a while.

 

[Steve Fractals]

I found in the end that these were leisure starter batteries but sold as deep cycle leisure. I got a refund and went LifePo4 and haven't looked back since. The system now just works and needs no interventions.

 

[Checkthisout]

I found in the end that these were leisure starter batteries but sold as deep cycle leisure. I got a refund and went LifePo4 and haven't looked back since. The system now just works and needs no interventions.

I get about 1.5kwh out of 3 8D batteries between 12.9 and 11.5 volts terminal voltage at slow draw. 720 ah rated.

They are "Marine Deep Cycle" so yeah. Wrong batteries for application deliver poor results.