Battery monitor pricing

Thornwave Labs is selling a wireless battery monitor (BT-DCPM) for less than 100 bucks.

pnichols wrote:
All flooded batteries I've ever owned down through the years have NEVER showed zero current flow whether on high voltage/current chargers for a day, or when on good old trickle chargers for days.

My batt meter shows zero current when my FLA batts are full. As a matter of fact, that's how I know if there's a problem like a broken cable or if they're not fully charged. They'll sit at .2 amp or whatever forever unless that last bit of "overcharge" gets in them.

Salvo wrote:
You can do auto zeroing and more functions for about $25. It's a DYI Arduino project. I have about 90% of it completed.

So actually this is kind of the conclusion I came to as well: DIY. Even thought I wouldn't actually save money if I valued my time at any reasonable $/hr, it would be a fun learning experience.

I would open source my code, so perhaps others could use it for their own rigs (or boats, etc).

pnichols wrote:
When I first start up the V10, the 130 amp Ford alternator often spikes to over 14.4X volts and to over 50 amps current flow into the coach batteries if the coach batteries are down a bit from our camping.

An update to my data above: Here at Quartzsite this morning, my alternator's output - with the V10 engine running merely at an idle - spiked to 80 amps for a quick non-solar non-generator one hour recharge of our motorhome's 230 AH AGM battery bank.

I don't know how Ford's 130 amp alternator does this, but some alternator designer(s) sure got it right with this one.

I'll try to post a photo one of these days. It won't be anything spectacular to look at with the three additional meters I have there, though ... just a stock Ford van dash. It's how the meters let me know how things are going that's important.

One 4-place voltmeter is plugged into one dash 12V receptacle. This stock receptacle is always ON (even with the engine OFF). I use it to, when the engine isn't running with the RV in storage, tell me what voltage a BatteryMINDer is currently pulse-maintaining the FoMoCo starting battery at - because I have a BatteryMINDer's output plugged into another always ON dash 12V receptacle. When the engine is running and/or we're underway, this same voltmeter tells me how much voltage the alternator is putting out to the cab systems and, supposedly, also to the coach battery bank.

Another 4-place voltmeter is mounted (Velcro'd) on the dash, but is plugged into a 12V receptacle back in the coach. This voltmeter, when the RV is in storage, roughly tells me what voltage the converter has on the coach battery bank (the rig is plugged into the house 24/7 between trips). When the RV is underway this voltmeter tells me what voltage the alternator is placing on the coach battery bank. If the starting-to-coach battery bank interconnect solenoid is operating properly (closes with the ingnition switch ON) - i.e. with no contact corrosion - then both voltmeters on the dash will read just about identical. They started reading unequal during our long trip this past fall probably due to interconnect solenoid contact erosion, so when we got home I had to install our THIRD interconnect solenoid in 9 years. The last two solenoids have been $$ heavy duty BEAR continuous duty solenoids with silver alloy contacts. This tells me how much stress there is on these contacts in hour after hour of driving with a 130 amp alternator bringing up a depleted 200+ amp hour AGM 12V deep cycle battery bank over and over. This voltmeter, since it's monitoring 12V system voltage back in the coach when underway, also tells me if I've failed to turn back ON the coach battery bank after gasing up (I disconnect the coach batteries when fueling because the For fill spout is close to the refrigerator gas flame.)

The third meter Velcro'd to the dash is a 3-place ammeter with it's shunt in the main negative lead of the coach's AGM battery bank. I ran the wires for this underneath the RV along the Ford frame so as to go between the shunt and the ammeter on the dash. This meter of course shows positive (being charged) or negative (being drained) amps that are flowing into or out of the coach battery bank. It indicates coach battery bank current flow activity when underway or when camped on hookups or with one of the generators running.

To summarize .... these three meters on the dash tell me:

1) How much voltage the engine systems are getting from the alternator.

2) (approximately) What voltage is on the coach battery bank terminals at all times.

3) Whether or not the alternator/coach battery interconnect solenoid is operating and if it's contacts are in good shape.

4) Whether or not I remembered to turn back ON the coach battery connect solenoid after gassing up so that the refrigerator doesn't unthaw when we're going down the road.

5) How much current the alternator is supplying - in real time - to the coach battery bank when underway.

6) If the coach battery bank is fully charged - regardless of whether the alternator does it or the converter does it.

7) How close to full charge the coach battery bank is getting - regardless of whether the alternator is doing it or the converter is doing it.

8) How much current every 12V item in the RV draws - by watching the 3-place ammeter on the dash change as I turn ON/OFF each item.

9) The general condition of the engine alternator system.

10) How the alternator's output voltage is regulated versus air temperature. At start-up, if it's cold outside, it will output up to 14.5 volts. When traveling in scorching tempertures, I have seen it's output voltage decline to as low as 12.9-13.1 volts.

When I first start up the V10, the 130 amp Ford alternator often spikes to over 14.4X volts and to over 50 amps current flow into the coach batteries if the coach batteries are down a bit from our camping. As we drive, the ammeter shows the current gradually taper over the next 4-6 hours to near zero amps as the AGM batteries reach full charge. Much of the time the current flow into the coach batteries ranges from 30 amps slowly declining down to 10-20 amps for long periods as we drive - before it further declines down to zero.

These three meters in combination can be very powerful tools for keeping an eye on things.

PNichols, I would be very interested in seeing a photo of your dash meters and perhaps advice on how to mount them. I also would like to see voltage and charging current while driving.

Bogart TriMetric 2030RV, from Northern AZ Wind & Sun

$155.00

I don't think that good old FLA RV batteries are accumulating amp hours when they sit there sucking 1-2 amps for days/weeks on a trickle - or any other - charger.

I think that long before the days/weeks have elapsed ... they are fully charged ... and what they are doing is just sitting there dissipating 1-2 amps of leakage current. RV AGM batteries (at least mine) don't seem to do this, thus making it very easy for me to tell when they're fully charged. I just look for near zero to zero current flow on the RV's built-in coach battery ammeter.

pnichols wrote:


...

I see "zero" when my digital ammeter's readout shows 00.0 ... but since it has only a 3-place readout, at this point - allowing for instrument repeatability errors - up to +0.1 amps or -0.1 amps could probably still be flowing through the shunt. But once the ammeter indicates this - it's a solid reading. Leaving the converter or alternator still connected to them, the AGM batteries do not pass any more current beyond this reading unless I run them down some then fire up the converter or alternator again. I call this zero ammeter reading point a "hard stop" in the AGM batteries' charging regimen. I've never seen this with good old liquid acid batteries ... they just continued to sit there and pass 1-2 amps for days.

...

If you had a 'fuel gauge' meter(FGM), is it possible you could see AHs accumulating even when you see a zero Amp reading? The math unit in a FGM may have enough significant digits but the display is truncating the Amp reading. After some extended time, the AHs should eventually show up as 10's of mAh.

It appears that with FLA, that those 1-2A might accumulate as AHs and then shortly after, the FGM would overstate SOC.

The answers are not worth $200 to me.

“In theory, theory and practice are the same. In practice, they are not.” ? Anonymous

HTH;
John

Salvo wrote:
I wasn't aware the OP has AGMs.

Is that true?

In fact, I do have AGMs, 4 x 110 Ah.