Poor Man's Trimetric?

I must smile at BFLs advance to appreciate why kWh has a place in battery management.

The best way is to establish your own personal, precise, CEF for your own personal battery bank. This is why I SCREAM about chargers not having the ability to be absorbsion voltage adjustable with at least 150% time allowance at absorbsion voltage limit to allow amperage to slump to 2-3% of total bank amp hour capacity. A few trials using a hydrometer will tell a person how long the battery must remain at this minimum amperage to have the batteries fill to capacity. Use the weak-sister cell of the bank and make life easier.

The CEF calibration should be performed every six-months with heavily cycled batteries. It isCRUCIAL to insure all cells are at maximum gravity before doing a CEF calibration.

Once a CEF calibration has been established voltage is used to insure both amperes and amp hours are stable for the C rate and return amperage minimum indication which tells you the batteries are full, INDEPENDENTLY of the amp hour or kWh meter reading. If the readings all agree which includes hours totalization of amperage or wattage then batteries are cgarged, performance is verified, and battery management reaches a new dimension with a 10-second glance at the meter.

A vital operation is the ability to reset or zero the meter. Everytime a non automatic zero rrsetmeter cycles to a new day the previous day's readings will bias current readings. When CEF is manually adjusted by past-zero-positive amp hours, it is vital to compensate for this as the meter has no idea which day is involved so CEF has to be manually calculated. Meters that have manually settable CEF are only useful if CEF compensation (not available on all meters) can be adjusted percentage point by percentage point to YOUR exact CEF definition.

This is a lot of information that should be discussed segment by segment to make it more comprehensable for the average Joe.

smkettner wrote:
Voltmeter is all you need.
Start charging at 12.4 to 12.1 volts under light load. Be aware of the time if you have limited generator hours.
Stop charging 60 minutes after battery hits absorption voltage.
Repeat next day as needed.

Extended 48 hour charge upon return.

Yes same as before I got the Tri in the 5er, but what I want is to follow the action in the TC with its 120v fridge over maybe six days off grid with the solar getting some AH in and the loads taking some out with the bank declining in SOC over all.

The decision point is turning out to be in the evening after a few days whether to shut off the fridge and ride it out till it is time to go home, or whether there is enough reserve to get by with the fridge still on, with a look at the weather forecast for solar prospects. (also how long will the milk last, can we get a bag of ice to put in there, etc)

Can't wait till next morning's "morning voltage" when there is no solar input to screw up the voltage reading or any big draws either. Don't want to leave the fridge on all night with no solar input if it is getting close. The AH counter is the way to tell how close you are getting when voltage is going up and down.

Turning the fridge off and restarting later turned out to be futile. Once things warm up in the fridge it takes too long to get back to proper temperature if it ever does. So turning it off is a serious decision. Lesson: have a propane fridge!!!!

I can live without the Tri in the 5er, but do want an AH counter in the TC. I could just swap it over, but am looking at these low cost monitors. I don't know enough about them, which is why I am looking for some clues here. :)

Voltmeter is all you need.
Start charging at 12.4 to 12.1 volts under light load. Be aware of the time if you have limited generator hours.
Stop charging 60 minutes after battery hits absorption voltage.
Repeat next day as needed.

Extended 48 hour charge upon return.

brulaz wrote:
2 Oldman assumes the 13V and uses Wh = V x Ah

So 1000Wh / 13V = 77Ah

But your V will not always be 13V and any conversion will be slightly off.

The 13V assumption is the problem.

Might be easier to start with an idea of battery bank Wh when full and when half full, but that is with two voltages 12.7 and 12.1

ISTR Mr Wiz uses Wh. Maybe he can say how he does that.

So at least there might be a way to get " close enough" to an AH count, since there will also be a "low load-camping type resting" voltage same as now to use as a cross-check.

If both the OP monitors would actually work, then the price difference is the cost of having AH vs WH and whether that is worth it to not have to do the conversion.

2 Oldman assumes the 13V and uses Wh = V x Ah

So 1000Wh / 13V = 77Ah

But your V will not always be 13V and any conversion will be slightly off.

The 13V assumption is the problem.

Mex are you saying that 2oldman's conversion at 77 is not correct? If it is correct I could get the really low cost one and just do the conversion to AH--IF--the whole thing is likely to be any good at all.

Good point about calibrating the thing.

Methinks el BFL is looking for hour storage function hasta 300 horas amperes

ANY AND ALL amp hour or kWh meters should be tested for accuracy using a simple 100 watt 12-volt bulb and timer. Start with 12.7 volts in the battery and you'll end up with around 12.3 after a four hour test.

Establish lamp ampacity with a known reliable ammeter independent of the DUT

Connect load through shunt to battery

Tick off 240 minutes reasonably close.

The ampere hour tally should be close enough to 32.5 amp hours to not raise the hair on the back of your neck.

Charge the battery at C10 exactly the number of amp hours extracted plus fifteen . Not time, not voltage, amp hours. Right to zero plus fifteen percent (115%) .

If you started with a rested utterly full battery, and look at the ammeter amperage at the end of the charging regimen and 15% extra, and more than 3% of amp hour capacity is amping its way back into the battery.

Either the battery is really old, bad, or the meter is a laugh-track. 115% is a reasonable CEF* correction for a 2.75% flooded antimony battery. It's a bit liberal in fact. A really good battery should be in the 112% range.

Testing with a kWh meter is a lot more revealing, but it opens up heavy caliber (calibre for BFL) math, which many forum members are not comfortable with.

*Charge Efficiency Factor

The above test is realistic and surprisingly easy to conduct. A light bulb, lamp socket base few feet of dual speaker wire (12 gauge) and two battery charger clips. This gizmo is invaluable when looking for phantom battery drain, so it's not a waste of money. make the leads long enough and you won't have to do repair work by the light of the silvery moon.

NAPA stores stock the 100 watt 12 volt bulb. They are sometimes available coated in nylon to resist breakage. Get it and the battery clips here. Wire too. The bulb base is available at Home Despot. Ceramic or plastic. pull chain or plain.

1000 watts @ 13v = 77a

ergo: 1kwh= 1000 wh = 77ah

SEARS (CRAFTSMAN) sells one of these CLAMP-ON 400A AC/DC Current meter for around that price...

They also sell one for AC AMPS only so be sure you are getting the correct one...

Mine came in a nice carry case...



I made up a nice +/- 70AMP DC monitor setup from SURE ELECTRONICS EBAY CHINA for my battery bank using the TRANSFORMER DONUT idea back in 2008 but unfortunate these are not available any more at a cheap cost...


Roy Ken