House Battery Drops like a rock

[calbiker]

Why?
Shunts per my knowledge waste some energy, when most of us are very picky about it.
I start RVing, when shunts were not available to general public and for years voltmeter, or just timing what I use was adequate for me.
Now I have Bluetooth BMS, what would be lighting years ahead in technology.

Why? To eliminate problems like this one. Why do you think there's a fuel gauge in vehicles? Likewise a volt/current shunt is similar usage to a fuel gauge for the electrical system.

Tell me, how much energy does a 500A, 75mV shunt waist when conducting 70A? How much energy is waisted in his 10 awg cable?

 

[Kajtek1]

Again, for 30 years of RVing, never really needed it.
Voltage is parallel gauge.

 

[OldblueAccord]

Years ago HF was giving free meters (with some purchase amount) and I collected like 5 of them, still using.
The week point turned the probe wire, but 10 amp rated meter was reading 17 amp and all the numbers seem to be accurate.
I bought clamp meter since and clamp bring bigger error margin, when wire probes on the expensive meter bring the same number, the Chinese meter has.

Honestly there fine for low voltage work the leads are the big mystery.

Even on my cheaper non Fluke meters I use Fluke leads. Just a personal opinion from some one who is employed as an Industrial Electrician for the last 24 years.

 

[rollerbearing]

How much energy is waisted in his 10 awg cable?

LOL

BTW 10 awg copper makes a handy crude shunt provided your current is within limits.

1mV per foot per amp at 20C

To half answer the question - the power dissipated is 1mW per foot per amp^2 at 20C.

 

[calbiker]

LOL

BTW 10 awg copper makes a handy crude shunt provided your current is within limits.

1mV per foot per amp at 20C

To half answer the question - the power dissipated is 1mW per foot per amp^2 at 20C.

Not quite complete.

1. The discussion is units of energy, not power.

2. Lets give a hypothetical example. Let's assume 10 awg cable 6 feet, 12 feet round trip. With 10 awg having 1 mOhm per foot, total resistance is 12 mOhm. At 70A energy dissipated is 12 mOhm * 70^2 = 58.8 J every second.

3. The resistance of a 500A, 75 mV shunt is 0.075V/500A = 0.15 mOhm. The energy the shunt dissipates is 0.15 mOhm * 70^2 = 0.73 J every second.

4. The cable dissipates 80 times more energy than the shunt.

5. @Kajtek1 had it all screwed up with his energy assessment.

 

[Hongster]

I just realized I have a clamp DVM but it can't check DC current

Need to buy one that have the capacity to check DC current.

 

[NomadEnergyClub]

Yes, a standard clamp meter only reads AC amps. For a parasitic draw hunt you want a Hall effect clamp that does DC amps, something like the Klein CL800 or the Fluke 376 FC. The nice part is you can read the negative battery cable without breaking any connections. The catch is that most clamps get noisy under about 100mA, so zero the jaws closed and empty before every reading and take a few readings.

If the draw you are chasing is small, a shunt based monitor gives a much cleaner low current reading. I put a Victron SmartShunt 500A on the negative post on jobs like this, then you can watch the draw on your phone overnight instead of standing at the battery with a meter. That also makes it easy to see the draw drop when you pull the right fuse.

 

[Hongster]

Yes, a standard clamp meter only reads AC amps. For a parasitic draw hunt you want a Hall effect clamp that does DC amps, something like the Klein CL800 or the Fluke 376 FC. The nice part is you can read the negative battery cable without breaking any connections. The catch is that most clamps get noisy under about 100mA, so zero the jaws closed and empty before every reading and take a few readings.

If the draw you are chasing is small, a shunt based monitor gives a much cleaner low current reading. I put a Victron SmartShunt 500A on the negative post on jobs like this, then you can watch the draw on your phone overnight instead of standing at the battery with a meter. That also makes it easy to see the draw drop when you pull the right fuse.

Thank you very much. But, I see what I can with what I have. I may go the old fashion way with disconnecting the negative cable on the battery and hook my meter in series to check for current draw.

I'll let you know when I get around to it

 

[rollerbearing]

Turn everything off - then pull each fuse, one by one, while inserting your ammeter across where the fuse was. This will show you the current through each branch circuit. I find it to be easier and faster than inserting a meter or shunt at the negative post. It will allow you to the measure the many parasitic loads on your panel. However, if the current is bypassing your fuse panel, then this technique will not find it and you will have to go to the negative post.

 

[autostaretx]

Here's a reasonable (i.e. $50) clamp-on DC ammeter (and general multimeter) that i have and can recommend.

The "%" scale is useful for looking at Sprinter systems that use PWM (pulse-width-modulation)

--dick

 

[OldblueAccord]

In those ads I always like when there are testing AC voltage and not using any Arc flash protection at all. Big plus one there....

 

[RoadsideSparks]

Fastest way to pin this down: pull one fuse at a time while watching a clamp meter or SmartShunt reading at the battery, and see which fuse kills the draw. Narrows it from "somewhere in the 12V system" to one circuit in minutes.

Common culprits that don't look "on": a stereo head unit that never fully sleeps, keyless entry/alarm module, an inverter left in standby (some draw a few mA even switched off), or a solar controller/BMS polling with no load. 1V/day is a real draw, not self-discharge.

Wrote up the full diagnosis process here:https://mejorfresadora.com/en/battery-draining-overnight/

 

[OldblueAccord]

Putting a cheap meter in series is a big amateur knock. No offense.

Good luck with what your doing. May the AI god be with you.

 

[rollerbearing]

Using a clamp dc meter at near zero current levels requires some extra attention to technique and careful interpretation of what you are seeing. For accurate measurement of low level currents I'll take a series inserted DVM type meter most any day provided there is easy and safe access to do so. Cheap or not. Analog even.

 

[autostaretx]

Using a clamp dc meter at near zero current levels requires some extra attention to technique and careful interpretation of what you are seeing. For accurate measurement of low level currents I'll take a series inserted DVM type meter most any day provided there is easy and safe access to do so. Cheap or not. Analog even.

To use a clamp-on in low current situations, "simply" wrap the current-carrying wire multiple times around the clamp.
Two passes through the clamp doubles the sensed current.
Four passes doubles it again.

I agree that a cheap meter in a series hookup merely risks blowing its internal 10 amp fuse.

--dick

 

[rollerbearing]

To use a clamp-on in low current situations, "simply" wrap the current-carrying wire multiple times around the clamp.
Two passes through the clamp doubles the sensed current.
Four passes doubles it again.

I agree that a cheap meter in a series hookup merely risks blowing its internal 10 amp fuse.

--dick

Agree - and zero before each measurement near the cable you are measuring. And good idea to flip the clamp 180 and read again - if zero is stable only the sign should change.

 

[calbiker]

To use a clamp-on in low current situations, "simply" wrap the current-carrying wire multiple times around the clamp.
Two passes through the clamp doubles the sensed current.
Four passes doubles it again.

I agree that a cheap meter in a series hookup merely risks blowing its internal 10 amp fuse.

--dick

Usually you don't have that luxury to be able to loop the wire around the clamp a few times in a vehicle.

BTW, the clamp you mentioned can measure down to 0.01A. It has an error of +/- 5 counts. That means if you're reading 0.05A, the actual reading can be anywhere from 0 A to 0.1A.

 

[rollerbearing]

@autostaretx

I remember this set up of yours - nice opportunity for x10 multiplier!

Post in thread 'How to test Solar Panels?'
https://sprinter-source.com/forums/index.php?threads/65466/post-650354

 

[autostaretx]

I remember this set up of yours - nice opportunity for x10 multiplier!

True ... it would'a been.

I was just focused on getting "roughly 5 amps" from each of my two panels on a scattered-cloudy day.

I've done the "loop the wire" test a couple of times, just to verify that the facts support the principle.

--dick

 

[DINO67]

If you have propane the battery shutoff may not shut off the propane leak detector. Also if you have a propane switch left on there will be a draw from the electric solenoid valve. Do you have a physical battery disconnect switch?

When I first brought my rig home I found there was a 300 watt inverter left on which would drain the batteries pretty fast even idle, but the physical battery switch needed to be on for this to happen.

Look for anything else the previous owner might have connected pre-battery disconnect.

Hello. I have 2005 T1N new to me this year. Im interested in installing an inverter to run a starlink and power up a computer for remote work. Currently van has lead acid house battery. I am interested in switching it out to Lithium Ion. I have propane and a battery shut off. Any advice on setting up an inverter? size? Hook it up directly to house battery?
Im new to the forum too, so I dont know if someone else already covered this in detail with info.
Thanks