Battery monitor pricing

[Gerald55]

I understand the need for a battery monitor - certainly the analogy of monitoring your fuel level via a fuel pressure gauge strikes home (although it's a little bit off). I want to get one.

What I can't get over is the price. They seem to hover at the $200+ level, and many don't even include the shunt. For things like battery and solar panels, it's pretty easy to understand how the material costs put some floor on the prices, and that once the cheaper manufacturers have come in and gotten close to the floor the prices are pretty reasonable.

As I understand it though, the battery monitory is really just a cheap microcontroller reading the voltage drop across a shunt, and a cheap display + the (fixed cost) programming to do coulomb counting. A few dollars of parts all in all. Where are the vendors coming in to undercut these $200 units?

Often you find the equivalent of battery monitoring technology built into inverters or other electronic devices, at no noticeable impact to the cost. So on top of the above reasoning from first principles, we know for a fact they are added to all sorts of devices at close to zero cost.

Is the market just too small? There aren't enough units sold to bother entering the market? I guess the presence of small niche manufactures like Bogart would help justify that idea.

It seems like it may be an interesting project for someone to develop the some open source battery monitoring software (that's the only "tough" part - i.e., not available off the shelf), and then pretty much anyone could throw together a monitor with a cheap microcontroller (e.g., TI launchpad for $5) and whatever display you want...

[razvan1t]

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

[mena661]

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.

[Gerald55]

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]

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.

[pnichols]

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.

😎 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.

[Harvey51]

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.

[allen8106]

Bogart TriMetric 2030RV, from Northern AZ Wind & Sun

$155.00

[pnichols]

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.

[full_mosey]

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

[Gerald55]

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

Is that true?

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

[pnichols]

full_mosey wrote:
So do we now have a definition of fully charged without float?

Yes we do, I think ... but I thought I always did.

I merely use K.I.S.S. to keep my RV life simple. Whenever my coach battery bank ammeter shows zero plus or minus current flowing in the battery bank's negative cable (that's where I installed the ammeter's shunt) going to the vehicle's ground point while converter or alternator voltage is being applied to the battery bank ... I call my coach battery bank fully charged.

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.

As I've stated many times, our AGM battery bank reaches this hard stop in recharge current acceptance from the alternator within only a very few hours of driving. Reaching this point of course takes longer using only the 13.6 volt fixed voltage converter - as is to be expected from the recharge time charts/graphs. In this drycamping situation I do only about 50-90 SOC cycles .... which are of course quicker than what it would take with liquid acid batteries. We don't much drycamp for days at a time in one spot, but when we do I mix in some alternator recharge time to ensure that the AGM battery bank gets to full (a zero reading on the ammeter) once in awhile.

Note BTW, that the recommended float voltage for my Fullriver AGM batteries is around 13.6 volts (@ 77 degrees). I shopped for Lifelines at first, but rejected them (after finally calling the company) because they insisted that a 13.6 volt float voltage was too high for Lifelines. I didn't want to slowly dry out Lifelines, so I went with Fullriver due to their float spec and also after discovering that Fullriver in fact made the AGM batteries for Rolls-Surette.

[full_mosey]

pnichols wrote:

...
http://www.batterien-mueller.de/uploads/media/Fullriver_Lade-Anweisung.pdf

Phil;

I see no material difference.

Lifeline 5.4 Charging(omitting 6V specs):
Absorption charging stage. A voltage limit of 14.3volts ± 0.1volts should be used when the battery temperature is 77°F(25°C). The battery is fully charged when the current drops below 0.5% of the battery’s rated capacity (0.5A for a 100Ah battery).

Lifeline format with Full River(FR) specs:
Absorption charging stage. A voltage limit of 14.7volts should be used when the battery temperature is 77°F(25°C). The battery is fully charged when the current drops below 0.024% of the battery’s rated capacity (0.024A for a 100AH battery).

FR gives a formula in Figure 1 to calculate the end of Abs; I2 = 0.012 * 0.02 * c20.

0.012 * 0.02 is a constant 0.00024, or 0.024%

On page 2 we find:

The profile in Figure 1 can be used with or without the float stage. Without the float stage, recharge can be terminated based on time (this will need to be determined as it will vary with depth of discharge and charge current) or percentage recharge (~105%-115%)(italics are mine)

So do we now have a definition of fully charged without float?

HTH;
John

[pnichols]

One thing to consider regarding a battery monitor is "where to put it".

We're in a small motorhome, so I put our RV battery ammeter and voltmeter on the dash so I can see them when driving down the road or when camping.

The ammeter shunt is in the negative lead of the coach battery bank, so it monitors actual current going into, or out of, these batteries. The voltmeter is not connected directly to the coach batteries - it is instead connected to a 12V receptacle in the coach. Having the voltmeter reading from this point tells me, while driving down the road, whether or not the refrigerator has power - so we don't wind up having traveled for hours with a non-operating refrig if it should not have, or lose, 12V power while we're underway (... such as if I should forget to turn the coach battery disconnect switch back ON after refueling at a gas station).

I watch the ammeter while underway to make sure that the engine alternator is properly charging the house batteries - as I'm about to install my 3rd solenoid that has failed in 9 years that automatically connects the house batteries to the alternator whenever the engine is running. This solenoid's contacts corrode over time and become resistive instead of being a short - which doesn't stop the alternator from charging the house batteries, but does slow the charging rate way down such that one can arrive at the next campsite with the coach batteries not being fully charged.

If our RV was a towable, I'd definitely want at least a voltmeter on the dash that was wired to monitor the actual trailer's or 5'er's 12V system to make sure it was powered at all times for the refrigerator's sake.

[doughere]

Gerald55,

This is your chance to make a killing. Manufacture for $20, sell for $100.

Doug