How to choose a battery monitor, which amp rating 30, 100, 200?

QQQ

Member
Sorry if this has been asked before however I cannot find an answer.

Want to buy a battery monitor for my camper, currently it has a group31 105 amp hour battery, next year I will be adding another of the same battery.

When buying a meter will a 30 amp work? or do I need a 200 amp, I don't know how that rating on the meter correlates to ratings on the battery. The camper is has all LED lights, fantastic fan, and an Engel fridge.
 

Rando

Explorer
Which meter are you looking at buying? For most actual battery monitors (Victron, Xantex etc) the meter is the same, you just need an appropriate sized shunt.
 

QQQ

Member
The cheap meter they sell on amazon or ebay, not sure I can post a link.

The meters come in 30/100/200/300 amp. What does the amp rating correlate to, how many amps you'll be drawing or the amp hour rating of the batteries.

There is no information that I can find that specifically tells you why they offer different amp battery monitors and which one is appropriate for your application.
 

dwh

Tail-End Charlie
The amp rating on those "Watts Up" style monitors is the rating of how much amperage can flow through the internal shunt before the magic smoke gets out.

With a good meter like a Bogart Trimetric or a Xantrex Linkpro, the shunt is seperate.
 

QQQ

Member
Yeah, it's tough putting the smoke back in, lol.

Looks like a 30 amp will suffice, however if it isn't going to hurt anything I will get the 100 amp, the cost is negligible and I'd rather have too much than not enough. The monitor comes with an external shunt.
 

jonyjoe101

Adventurer
I been using the same 90 volt 30 amp combo meter going on 4 years, its always on 24/7. Its connected between the controller and battery. It can measure amps going into battery and also amps going out (bidirectional). If you need anything more than 30 amps you probably have to connect that device to the battery.
The led ones are the best to get, they got big numbers you can read in daylight. I only paid 20 dollars for it, no shunt required for the 30 amp one.
combo.jpg
combo meter.jpg
 

john61ct

Adventurer
In order to accurately measure SoC - which even expensive shunt-based BMs don't do all that well - ALL currents in and out of your bank pass through that shunt.

So your shunt needs to be sized to handle - plus 25-30% safety margin - the **highest possible** simultaneous current flow total.

Starters often pull well over 100A.

Big stereos lots more than that.

Some people have alts that put out 360+A.

All depends on your setup.
 

john61ct

Adventurer
SmartGauge is more accurate, more user friendly and doesn't use any shunt.

Only works with lead though, not LFP.

And doesn't record amps, just SoC and current, on two banks.
 

QQQ

Member
The camper is a taxa cricket, it only has LED lights, a endless breeze 12v fan, Engel fridge, and a water pump and 12v water heater which will almost never be used.

Next year plans are to add a solar panel and another battery. The camper is prepped with zamp solar.

Looking to put a simple meter in so I know what the battery voltage is and I like being able to see the what the amp load is. The pic above is the monitor I am looking at can get it on fleabay for about $30.

If 30 amps is enough then I will get that and won't have to wire in the shunt.
 

QQQ

Member
"Dont forget to use two OCPDs, one for each meter lead"

I don't know what that is, just going to following the wiring instructions they print on the side of the box :)
 

john61ct

Adventurer
The shunt resistance has to match the BM, best to buy the shunt from the BM vendor.

You seriously need to **know** the max current in Amps that will go in or out at any one time.

For a Bogart Trimetric on a big LFP bank I installed 1000A.

All the Blue Sky batt switches are rated 300+A, many 500A.

If a Starter is involved I would go 200A minimum, or 30% above the biggest charge source.

And voltage does not give you SoC with any accuracy.

I recommend SmartGauge

Trimetic or Victron BMV-702 fir counting AH.
 

QQQ

Member
No starter involved, only the items mentioned previously. Thx for the info, the trimetric is nice however too expensive for my requirements.
 

DaveInDenver

Middle Income Semi-Redneck
No starter involved, only the items mentioned previously. Thx for the info, the trimetric is nice however too expensive for my requirements.
Is the battery connected directly to the alternator? If so that will be the current limit (e.g. biggest charging source + 30%) you should use for the shunt. A discharged battery with an otherwise lightly loaded charging system (headlights off, starting battery topped, etc.) means the alternator would have a significant amount of its capacity available to give to the aux battery. The shunt has to handle all the current going in (charging) and out (loads) of the battery.
 

QQQ

Member
There is no alternator, it is a Taxa cricket camper, this was mentioned in an earlier post.


My goal is to put a battery monitor on it so I can keep tabs on the battery and my original question was about the amp rating of the monitor.
 

dwh

Tail-End Charlie
"Dont forget to use two OCPDs, one for each meter lead"

I don't know what that is, just going to following the wiring instructions they print on the side of the box :)

Over Current Protection Device. Translation: fuse or breaker.
 

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