Small stand-alone amp meter?

[pugslyyy]

Full disclosure: I do not have a SmartGauge; I use a pair of hour counters, the TriMetric and the hour counter in the Blue Sky solar controller.

The SmartGauge's claim to fame is that it is easy to install and, once programmed correctly, will give you a decent state of charge reading. Does it work? Handy Bob swears that it cannot work but Chris Gibson, the gentleman who developed it, started out programming hour counters and developed the SmartGauge because of his dissatisfaction with hour counters.

You money, your choice. ;-)

I think for me the troubling part is that there is no explanation as to how the SmartGauge works except "it's proprietary". I would feel better about it if there was some discussion on the methodology. As an electrical engineer I find it hard to believe in a device like this when I don't have some basic understanding of how it functions.

 

[DiploStrat]

Jon, Chris Gibson loves nothing so much as to geek. While he is not going to give away the farm, you can read more here, including his argument against hour counters. As you might imagine, electronic blood flowed (at least at one time) on the UK narrow boat fora. (One example: http://livingonanarrowboat.co.uk/forum/living-on-a-narrowboat/battery-monitors/)

Happy geeking:

-- http://www.smartgauge.co.uk/sgadesc.html

-- http://www.smartgauge.co.uk/sgvahrs.html

Note that each of these links has sub-links.

The worst criticism that I have heard is that the SmartGauge is a bit like a volt meter in that its readings are most accurate when the batteries are at rest. The best argument in favor is that it is bone head simple, hence its use on military vehicles.

I would add another thought: To a degree, it doesn't matter. What you want is a charging environment (set of systems) which charges at every opportunity and to completion. That is, I don't look at a gauge and say, "Oh my, I wonder if I should charge the batteries?" With lead acid batteries the answer is always "YES!" (As you know, I do geek the degree of discharge, etc.) At the present time, the best set up that I know is good bulk charge from the engine and good absorb charge from solar, both working automatically. Thus it may be argued that the best argument for some form of SOC meter is to tell you when your automatic systems are not enough and you need to go to shore or generator power.

Edited to add: Would love your thoughts.

 

[Bbasso]

so my current system, absorption from solar bulk from engine is about it sound as it gets without getting into seriously huge money. So I'd like to mention before maybe I should have some faith in what I built...

 

[DiploStrat]

AFAIK - Yes

Rob,

There are three major requirements for charging a lead acid battery:

-- A voltage high enough to overcome internal resistance and low enough to avoid boiling/overheating the battery.
-- A current high enough to replenish the energy lost.
-- Lots of time to let the battery fully absorb the charger.

The balance between voltage and current is important - high voltage but low current won't do much and neither will high current and low voltage. Conversely, high voltage and high current will kill the battery. A good charge controller will balance these.

Another point to remember is that for best life a lead acid battery wants to be drawn down as little as possible, at the lowest rate (Peukert's effect), and recharged as quickly as possible. Go over to RV.net and you will read questions like, "How do I know when to recharge?" Silly question; the answer is always "Immediately." Indeed, you can actually exceed the 50% rule if you recharge immediately. Conversely, if you cannot recharge quickly, you should limit your discharge as much as possible.

For the typical RV, going from campground to campground with full hookups, this is not much of an issue. Their batteries are too small and their recharge from the engine or even shore power is not very good, but it doesn't really matter, they are plugging in for twelve hours a night - perfect.

For the overland or expedition camper, this reverses; here we have a vehicle that hopes to go for weeks without ever connecting to shore power. This puts a premium on:

-- Lots of amps from the engine alternator. The good news is that most modern vehicles can produce over 100A; a kind of "magic" number as, depending on the depth of discharge, your battery may not take much more than 100A and certainly not for very long, and,
-- Lots of time. Since most of us drive less than six hours a day, it is here that solar excels. With a good bulk charge from the alternator, the charge rate will drop down to the 15-30A rate that can be provided by a 200+w solar array.

Things to watch:

-- Small wiring: Low voltage, high amperage circuits need BIG wires. A camper with 10 AWG between the starter battery and the camper battery will see poor performance. Things get much better when you reach 1/0 AWG or larger. Even solar panels are typically connected with wires that are too small.
-- Low voltage: For lead acid, open or AGM, the voltage needs to be well above 14v at 70F. Thus a diode isolator is the kiss of death. Similarly, I hear reports of various Toyotas and Sprinters running at less than 14v. In these cases, you may be in the market for some form of battery to battery charger, such as those sold by Sterling or CTEK.

None of this is hard, it is merely complex and the devil is in the details.

 

[Bbasso]

I hear ya I hear ya, I think I've done it correctly so far. What I have is 0 gauge running from the starter battery to my ACR and 0 gauge from the ACR to the house batteries.
from the solar panels to the controller I have mc4 cable and from the solar charge controller to the house batteries (shortest distance possible) I am using 10 gauge wiring.
Included in the mess would be Blueseas fuse box, blue seas dual USB outlet, Amazon cheapo volt gauge and other stuff I can't remember lol

My biggest concern is how much am I putting in to the batteries through the ACR and how do I know when my house batteries are full so I don't overcharge them.?.?

I can go 3 or 4 days without any sunlight (rain) and not go below of 12.7, I am very power conscious, nothing is plugged in unless it's being used, except the refrigerator so my power should last quite a while.

But I feel like I need some kind of monitor because I really can't see what's going on... I'd like to be able to know so i can prevent any headaches or costly repairs that aren't needed.

 

[pugslyyy]

My biggest concern is how much am I putting in to the batteries through the ACR and how do I know when my house batteries are full so I don't overcharge them.?.?

Unfortunately it is a bit more complicated than that. Think of charging a battery less like an on/off valve and more like water flowing from a tap. You use a SMART CHARGER (AKA a 3 Stage Charger) to regulate the "tap".

Here's how it works.

In the beginning, you have the tap full on - water gushing into the (hopefully not more than 50%) empty container. As the container gets fuller, you gradually close the tap reducing the flow of water to a trickle. We generally talk about three states of charging - bulk, absorption, and float.

BULK is when the tap is full on and you are pouring as much into the battery as you can, usually until it is about 80% full. This usually takes an hour or two, or with a powerful alternator / charging system as little as half an hour.

ABSORPTION is when you reduce the flow, usually from 80% to 90 of 95% full. This can take another couple of hours.

FLOAT is just a trickle, which usually kicks in about 90-95% (exact numbers depend on the battery, smart charger, etc). This can take as much as 6-8 hours.

(This is why Diplostrat talks about using an alternator as an ideal charging source for the BULK stage and solar as an ideal source for the FLOAT stage.)

 

[DiploStrat]

…
My biggest concern is how much am I putting in to the batteries through the ACR and how do I know when my house batteries are full so I don't overcharge them.?.?

YOU don't have to worry about overcharging; your charging systems take care of that.

Grossly, as the voltage of your battery rises, its ability to take a charge drops and the charger responds by cutting back on amperage. This is true of your vehicle's charging system, your solar controller, or your shore charger. There are, of course, differences in the exact profile of each device but they all work the same way.

This isn't to say that a monitor isn't nice to have, after all, I have two, but merely to point out that it is more important to assure that your battery is connected to a good charge source whenever possible.

A slight refinement of Puggslyyy's post; I like solar for the absorb stage as this is typically the longest and the stage where high voltage is the most important. I never sit still long enough to ever worry about float.

 

[Bbasso]

YOU don't have to worry about overcharging; your charging systems take care of that..

I'm So Happy to hear that!
I was afraid of blowing up the batteries, ahhhh...

 

[LeishaShannon]

The "smart" gauge isn't compatible with all battery types (ie. Lithium) so if you upgrade in the future you may be left having to buy a proper coulomb counter like the Victron BMV 700 series anyway.

 

[Bbasso]

How about a simple thing like...

An amp guage that shows how much is going from my ACR to my house batteries?

 

[Bbasso]

Oh...
My bad, I should have known better!
LOL

 

[pugslyyy]

How about a simple thing like...

An amp guage that shows how much is going from my ACR to my house batteries?

You need to go back and re-read the first posts in this thread. Ebay. $10. Done.

 

[Joe917]

The OP asked for an amp meter originally, once they explained what they wanted it for it became obvious they did not want an amp meter but a monitor.
We have been full time over a year, never plugged in(230 volt tuck in US) almost never use battery to battery charger, solar does it all (630 watts)
We use a Trimetric monitor which shows: amps in or out, battery % charge, days since full charge, days since equalized, volts of house(not much use), volts of starter battery(handy).
Highly recommended