lifepo4 coulomb capacity LCD meter

[John61CT]

Sounds right.

You happy with the unit so far, how long you had it?

 

[Jmel]

Sounds right.

You happy with the unit so far, how long you had it?

Only had fridge for about 2 weeks maybe.

So far I like it a lot. Especially for $335. Lots of space, and very simple. Lower amp draw than the new models, and no gimmicky USB charger. I have enough of those.

 

[Jmel]

Just now checked the meter. 98.3% charged , voltage at 14.6 and solar is dumping .8a into battery. I'm sure it could deliver more but it is at nearing the end of the cycle...

Temps hit upper 30s last night, so I'm sure fridge didn't run much.

 

[John61CT]

Is that charging an LFP bank as per the thread title?

 

[Jmel]

Is that charging an LFP bank as per the thread title?

No, I'm charging AGM batteries. I've only been posting here because I bought the meter. Meter works with several chemistries.

 

[John61CT]

OK good.

When amps into the bank fall below 1A per 100AH, that is the definition of 100% Full. Unless mfg specs a different tailing amps rate like .005C or .015C

Can you tell the meter that, manually reset it to 100%?

 

[Jmel]

OK good.

When amps into the bank fall below 1A per 100AH, that is the definition of 100% Full. Unless mfg specs a different tailing amps rate like .005C or .015C

Can you tell the meter that, manually reset it to 100%?

Unfortunately there are only the 3 options; capacity, full voltage and empty voltage. By default, 0 for full and empty is recommended for lead acid. 

I can manually reset to 100 by specifying a full and empty voltage manually or by simply power cycling the meter.

I'm using a sunsaver duo controller. I charge 10% to starter battery and 90% to house batteries. I just bought a modbus adapter to view detailed logging info and have the ability to change several settings in the controller. Should arrive Monday.

 

[John61CT]

So as I thought, that meter is **only** using voltage for (roughly) estimating SoC.

Not saying that's bad, certainly simpler for users.

So when you see the tailing amps drop below your more accurate Full point, note the voltage at that time, if SoC is below 100%, drop the full voltage setpoint until the gauge is calibrated.

Do you have 0% set to 10.5V?

 

[Jmel]

So as I thought,  that meter is **only** using voltage for (roughly) estimating SoC.

Not saying that's bad, certainly simpler for users.

So when you see the tailing amps drop below your more accurate Full point,  note the voltage at that time,  if SoC is below 100%, drop the full voltage setpoint until the gauge is calibrated.

Do you have 0% set to 10.5V? 

I have the meter set to defaults, which is 0 full volts and 0 empty. It has some built in logic to work with lead acid. The instructions I read said changing was only needed for other chemistries.

I felt the accuracy was 'pretty close' with the defaults. Only thing I changed was capacity, and I set that at 100 instead of 200 ah so it would show 0 percent when I'd used 100ah.

There are some YouTube videos showing the older models if you search for tk15 coloumbmeter.

I think the meter uses current to determine state of charge. It simply adds and subtracts from the total.

You can then override what it thinks zero and full are by telling it specific voltages for those conditions.

 

[John61CT]

But without the parameters I mentioned above, and no manual reset, AH counting would quickly become uselessly inaccurate.

It just has default voltages set internally when you leave them at zero.

 

[Jmel]

Well, so far it seems okay. Better than the ongoing 'upward' only counting from the watt meters. At least this device will use addition/subtraction to determine the capacity it counted amps towards. I didn't figure it would be super accurate, but when it is near 100 percent full, the amps are definitely only trickling in. When there is some heavy usage, it seems like the amps are pouring in, and the meter reflects a somewhat accurate number of amps drawn out. I guess it's 'good enough' as in, good enough for a general idea of where the charge is at. I don't expect super accuracy at 20 bucks though.

I can try it like this for a week, then use a smart charger to check amps back into the battery and see if it counted correctly. I can also set the full and empty voltages next week to see if that makes any difference. .

 

[John61CT]

Yes, good enough often is.

Just remember all batts especially lead, walk down their AH capacity, sometimes quickly.

If your 200AH bank is actually 140AH down the road, and you're still pulling 100AH from it each cycle. . .

That's the beauty of SmartGauge, for an expensive lead bank, don't even jave to know the actual reduced AH capacity, it somehow stays accurate.

But not relevant to topics here, just background

 

[Jmel]

Good to know. As I was driving today, I was thinking about what you might be getting at, and sure enough, it is the reduction of AH capacity as the battery ages (I think ).

So yeah, I guess unless I reset the meter every so often, it will never hit 100% again. But then again - with a constant load on it (the fridge) I think it is unlikely I ever see 100% just due to the constant cycling of the compressor eating a few amps here and there.

I'll surely keep an eye on it.

 

[John61CT]

For longevity with lead you really should strive to get to true 100% every cycle. 98% might mean lots of wasted lifetime.

EndAmps is the Truth, calibrate your SoC gauge based on that.

Set the Full voltage to whatever you see at that .005C point.

Make sure all charge sources hold Absorb V to at least .01C, defaults usually mean Floats too soon.

 

[Jmel]

You bring up some excellent points here. My smart charger can put 15a max through the wire. And it took about 3 or 4 hours to charge it the other day with the panels off. The last hour or two were very low amps, like 5 or 6, until it got down to a very light trickle. I can tell the charger what the ending voltage per cell should be. It is at 2.4 by default. I tried 2.43 and 2.45 for a few moments to see what it would do, and it does indeed raise the voltage slightly.

When I get the modbus adapter for the sunsaver duo, I will have the ability to modify the absorb voltage and other stages. I'm not certain I should even change them, but I guess I can take the loads off the battery, put it on the smart charger, and watch it for what voltage yields .005c - correct?

Then, whatever that voltage is - I set the meter to have that number as full voltage. Empty would be 10.5 you say? I was thinking 11.4 or something - but if you say 10.5 I'll do it.

I'm a little lost on the 100% though... if a battery always has a cycling load on it, I don't know how it ever gets to 100% and stays there. The load just eats amps all over again when it starts up again.

 

[John61CT]

As long as loads are less than charge source amps no current is drawn from the batt, but only a shunt at the batt knows what it is absorbing.

The charge source usually has an egg timer to hold Absorb, you need to calibrate that based on max or avg loads.

If your bank is 300AH then .005C is 1.5A

Check mfg specs, that endAmps spec can vary.

Set charger to hold at mfg spec'd Absorb V, terminate at endAmps, let bank rest a few hours isolated, that is then "100% Full" voltage.

Yes 10.5V is 0% SoC for lead, you only want to get there (briefly) for controlled maintenance or testing protocols.

Will be interesting to set AH capacity properly, then draw down to gauge says SoC 50% compare to AH out.

 

[Jmel]

As long as loads are less than charge source amps no current is drawn from the batt, but only a shunt at the batt knows what it is absorbing.

The charge source usually has an egg timer to hold Absorb, you need to calibrate that based on max or avg loads.

If your bank is 300AH then .005C is 1.5A

Check mfg specs, that endAmps spec can vary.

Set charger to hold at mfg spec'd Absorb V, terminate at endAmps, let bank rest a few hours isolated, that is then "100% Full" voltage.

Yes 10.5V is 0% SoC for lead, you only want to get there (briefly) for controlled maintenance or testing protocols.

Will be interesting to set AH capacity properly, then draw down to gauge says SoC 50% compare to AH out.

I think I understand. I have a 200 ah bank, so 1.0A (as a starter). I think when I was using the smart charger, I'd played around with 2.43 volts per cell, and it was taking a few more amps than at 2.4, but I didn't do it for longer than 15 mins or so. In other words, at 2.4, the charger was satisfied and thought the battery was full, but when I upped it to 2.43, it would still dump a little more - say, .5 amps. 

I had the coloumbmeter set to 100Ah though, so that I'd never go below 100Ah. 

These are the specs on the battery:
---
Specifications
Cells Per Unit
6
Voltage Per Unit
12v
Operating Temperature Range
Discharge: -40 C~60 C
Charge:-20C~50C
Storage: -40C~60C
Capacity
100Ah@20hr-rate to 1.75V per cell @25C
Weight
Approx.. 30kg
Max. Discharge Current
1000 A (5 sec)
Internal Resistance
Approx. 5.0 mΩ
Normal Operating Temperature Range
25C±5C
Float charging Voltage
13.6to 13.8 VDC/unit Average at 25oC
Recommended Maximum Charging Current Limit
20A
Equalization and Cycle Service
14.2 to 14.4VDC/unit Average at 25oC
Self Discharge
Valve Regulated Lead Acid (VRLA) batteries can be stored for more than 6 months at 25C. Self-discharge ratio less than 3% per month at 25C. Please charge batteries before using.
Terminal
Terminal F15/F12
Container Material
A.B.S. (UL94-HB)

---

 

[John61CT]

Yes, increasing volts pushes in more amps.

That can lead to overcharging.

Best to get full charge profile info from mfg.

 

[Jmel]

I've sent the seller a question to ask about the absorb voltage. Sunsaver Duo manual page 9 shows ( http://support.morningstarcorp.com/wp-content/uploads/2014/07/SSD-IOM_EN_v2.1_MS-001164.pdf ) 14.1 absorb voltage by default, and 13.7 float. I've seen (I think) it at 14.4-.6 during the day easily though. Once I get the modbus adapter, I'll be able to more closely see what is actually happening.

More info here too on the defaults: http://support.morningstarcorp.com/wp-content/uploads/2014/07/SSDuoENG2_111.pdf (flyer with specs)

 

[John61CT]

I would not use a SC that didn't give full control over setpoints.

Important with AGM and GEL you don't overcharge, sensitive, and unlike FLA you can't put offgassed water back!