12v car battery monitor?

[cashcow]

Hello all,

I am looking into a 12v car battery monitor and stumbled on this one from amazon

https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS/

Looking at The diagram I see that they want the shunt to be placed between the battery negative and the chasis ground, but looking at the RAV4 EV battery set up I see 3 negative cables hooked to the negative on the battery. 2 I see going straight for the chassis ground of the car. The other goes into a hose and deep into the car to god knows where. Does this mean I have to place the shunt right between the negative of the battery and the connector where the 3 negative cables connect? Or can I just disconnect one of the car chasis ground cables and slip the shunt inbetween there? My concern is getting inaccurate readings if I don't connect it directly to the car battery before the 3 negative cables split section?

Does it have to be Negative Battery to Shunt then Shunt to 3 negative cable split.

OR

Negative Battery to 3 Negative Cable Split and PICK ONE of the negative cables... disconnect the chasis ground... and place the shunt in between?

 

[KurtManz]

Your insight is correct that for that to work you'll likely need to put it between the battery negative terminal and the 3 way split.
Doesn't the car already provide some power consumption from the battery on one of the info screens?

Are you worried about your battery getting to end of life? An easier solution could be a voltage monitor on the 12V port, something like this?
https://www.amazon.com/gp/product/B075RV7KRM/ref=ox_sc_saved_title_1?smid=A294P4X9EWVXLJ&psc=1

as a bonus it charges your phone and gives you a multicolor ambient light

 

[asavage]

I am looking into a 12v car battery monitor . . . Looking at The diagram I see that they want the shunt to be placed between the battery negative and the chasis ground, but looking at the RAV4 EV battery set up I see 3 negative cables hooked to the negative on the battery . . . Does it have to be Negative Battery to Shunt then Shunt to 3 negative cable split.

Generically, yup.

However, the answer really depends upon what you are trying to measure. But for most cases . . . yes, you have to have the measurement shunt in series between the battery's negative terminal and ALL of the load.

. . . and stumbled on this one from am-azon: https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS/

Since that model will only display current in ONE direction, consider upgrading to something that displays both charge and discharge. A cursory search found this unit at $39, which uses the shunt to measure and display both charge and discharge current. Based on user feedback, I don't think that's a good choice, but it illustrates the capability I'm referring to.

If you're going to run the wires, you may as well get the complete charge/discharge information. OTOH, the best choice depends on what you want to measure.

 

[miimura]

Hello all,

I am looking into a 12v car battery monitor and stumbled on this one from amazon

https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS/

Looking at The diagram I see that they want the shunt to be placed between the battery negative and the chasis ground, but looking at the RAV4 EV battery set up I see 3 negative cables hooked to the negative on the battery. 2 I see going straight for the chassis ground of the car. The other goes into a hose and deep into the car to god knows where. Does this mean I have to place the shunt right between the negative of the battery and the connector where the 3 negative cables connect? Or can I just disconnect one of the car chasis ground cables and slip the shunt inbetween there? My concern is getting inaccurate readings if I don't connect it directly to the car battery before the 3 negative cables split section?

Does it have to be Negative Battery to Shunt then Shunt to 3 negative cable split.

OR

Negative Battery to 3 Negative Cable Split and PICK ONE of the negative cables... disconnect the chasis ground... and place the shunt in between?

I have this exact meter hooked up to my RAV4 EV. However, I am using it to measure energy exported from the car's 12V system to an Anderson type connector. I designed and 3D printed a bracket to hold the shunt and a breaker next to the battery. The bracket mounts to existing threaded holes on the car. It turned out pretty well. I was disappointed to find that the meter does not register the reverse current flow.

In the image below you can see that I connected heavy 4 gauge wires to the positive and negative terminals of the battery and installed a disconnect on the negative post. I can therefore bypass the primary 12V battery and run the car from a battery connected to the Anderson type connector if necessary. A breaker was also installed in the positive cable which allows me to easily turn off the load.

 

[cashcow]

Hi Miimura

This looks VERY nice. I like it a lot. I have the same anderson connectors just haven't used them yet. Are you powering anything with a 12v pure sinewave inverter? I have a Xantrex prowatt sw 2000 inverter, but I haven't installed it yet because I think it would be better to just put it inside than to plug back and forth. Still the anderson set up is great.

Is it just me or did you disconnect one of the negative cables in the 3 way split on the 12v battery? I see two connected, but the third seems to be missing. Any reason? not needed? I believe 2 of those just went straight to the chassis ground. THe other one digs deep into the rav to god knows where.

Thank you savage for the other suggestion on the 12v this unit looks nicer and more like what I was looking for I'll be looking deeply into to. The connection method seems a little different at first glance, but it would just be my lack of experience with these.

 

[miimura]

It's not that clear in my picture, but the ground wires are all there. I think it was part of the JdeMO install, which added 2 aluminum L brackets and dropped the two smaller black cables lower down. The one with heat shrink on the lug is the 4th one I added on top of one of the L's.

Of course, a 120V AC inverter would be the primary use for the Anderson connector. However, I have also bought some equipment so that I can put some power from my car into my Powerwalls should I experience an extended power outage during the winter when my solar is generating very little. I basically want to be able to pull 500W from the car into the house with a grid tied inverter so that I can prevent the Powerwalls from going totally empty overnight. I have heard that once they shut down due to low SOC, they won't start up again until they can sync to the grid. In an extended outage I just want to make absolutely sure that they never shut off. Anyway, I just got the last piece today so I haven't tested it out yet.

One other use for the Anderson connector would be to temporarily use a LiFePO4 battery so that the RAV can stay on in READY for extended periods of time. I went camping in July and left the RAV on for more than 24 hours straight to run an electric cooler. The Bosch AGM battery did not like it and I discovered that it was overheating and venting. I don't know how long it was in that state, but I'm sure it is damaged even though I see no evidence of that now that a month has passed. Anyway, I also ordered 4 used 38120 Headway high current LiFePO4 cells off eBay and will build it into a "12V" pack so that I can bypass the Bosch battery with the negative terminal disconnect already installed. It will only be used for this long duration parked in READY situation since it won't have the capacity (8Ah) to be used for standby. The standby capacity is what the Bosch AGM is good at.

 

[dstjohn99]

...I have also bought some equipment so that I can put some power from my car into my Powerwalls should I experience an extended power outage during the winter when my solar is generating very little. I basically want to be able to pull 500W from the car into the house with a grid tied inverter so that I can prevent the Powerwalls from going totally empty overnight. I have heard that once they shut down due to low SOC, they won't start up again until they can sync to the grid. In an extended outage I just want to make absolutely sure that they never shut off. Anyway, I just got the last piece today so I haven't tested it out yet.

I'm am so looking forward to hearing more about this!!

 

[miimura]

...I have also bought some equipment so that I can put some power from my car into my Powerwalls should I experience an extended power outage during the winter when my solar is generating very little. I basically want to be able to pull 500W from the car into the house with a grid tied inverter so that I can prevent the Powerwalls from going totally empty overnight. I have heard that once they shut down due to low SOC, they won't start up again until they can sync to the grid. In an extended outage I just want to make absolutely sure that they never shut off. Anyway, I just got the last piece today so I haven't tested it out yet.

I'm am so looking forward to hearing more about this!!

I just posted about it on TMC.
https://teslamotorsclub.com/tmc/threads/powerwall-2-0-backup-runtime-extender.126358/