Need to rewire the TM-2030 battery monitor.

[oletimer]

We have just picked up our new 5th, and had removed all our solar, controller (TS-MPPT-60), monitors, etc. from our old 5th to be installed on the new unit. That installation has some of the grounds going to the wrong side of the shunt, so the reading on the monitor is incorrect. I installed everything on our old 5th, so I can fix that OK, but upon inspection of the battery bank (10/6V/AGMs) I noticed the cables from the invertor(Magnum MS2812) hookup kinda' mid-bank. When I installed the inverter in the old camper, I hooked the + cable to one end of the bank, then the - all the way to the other end of the bank. I always thought that would be more efficient. Am I wrong? It will be more difficult to rewire the battery bank rather than just the shunt, as there are several load wires hooked up mid-bank as well. How much efficiency would I loose? I am also wondering if the chassis ground is large enough, it looks like about 2 ga. Some of my old cables were used, so the cables from the inverter to the first battery is 4/0, with a run of less than 4'. Thanks for any comment. Dick T

[mptjelgin]

Check out the various battery wiring diagrams on this page:

 

http://rvroadtrip.us/library/12v_system.php

 

You'll note that for a "perfectly balanced draw" they are picking up both the positive and negative from "mid bank". My 4-battery system is wired this way.

[Jack Mayer]

Take a look at the efficiency increases from different wiring techniques HERE. I'm sure it will be enlightening. Personally, I'd rewire the bank but it is not as bad as all from one side.

 

#2 ground is "maybe OK", but it really should be wired with the same size as the rest. I would have used the 4/0.

[oldjohnt]

If you want detailed technical information regarding how best and better balanced battery combinations are to be configured, check out the Smart Gage Literature. They show examples of different connections and the current and charging balance each method achieves, from the simplest + off one bank - off the other, and its quite amazing how much difference each can make. While a lay person may mistakenly think big cables are extremely low resistance so it doesn't really matter how I make my connections, if you study the Smart Gauge data you will find that's incorrect. However its each persons own batteries and money and their choice of how they choose to wire them, perhaps their method is better then what Smart Gauge suggests?????

 

http://www.smartgauge.co.uk/batt_con.html

 

John T

[Yarome]

I noticed the cables from the invertor(Magnum MS2812) hookup kinda' mid-bank.

 

I always thought that would be more efficient. Am I wrong? It will be more difficult to rewire the battery bank rather than just the shunt, as there are several load wires hooked up mid-bank as well.

 

I am also wondering if the chassis ground is large enough, it looks like about 2 ga.

 

so the cables from the inverter to the first battery is 4/0, with a run of less than 4'. Thanks for any comment. Dick T

 

Just splitting hairs.. you might have meant 'to' the inverter rather than 'from'. With that large of a battery bank, it is actually more "efficient" in terms of the life of your batteries, wiring mid-bank helps balance the draw across all of your cells more equally (providing all cable length runs are also equal). HOWEVER, by-passing your shunt 'will' affect your battery meter readings. All loads should be downstream of your shunt to take full advantage of your trimetric.

 

Personally, I prefer wiring end to end (vs mid-bank) in almost all cases. It simplifies and improves efficiency on the 'back-end' of your electrical package. IMO

 

Chassis ground. It depends on how long the run is, but I would consider 2ga to be too light. It's generally such a short run, but all-important, so I certainly wouldn't scrimp on the ground. With a 10x6v bank.. there is the potential to have some pretty heavy draws.. but I don't know how your wired so I can't comment directly. Use a decent calculator and figure a 125% load of the maximum potential of your hardware across your run distance (that's actual distance x2). KWIM? Just off the cuff with a 4' run.. I would want to go 1/0, but 2/0 would be better.

 

From the battery to your inverter with 4/0.. NOW you're talkin! 'Overkill' if you "go by the book", but if you got it.. use it across the whole bank.

[oldjohnt]

The thing to consider if sizing a common "Ground" return cable is while several different cables might (subject to wiring scheme) carry current to different loads, a single common ground return cable can carry ALL currents combined SO DONT SCRIMP. When you're only working with 12 volts to begin with, you really cant afford to be dropping like one or too many tenths of a volt across too small cables. I would consider sizing "by the book" as the MINIMUM I would use, while over engineering or over sizing within reason a desirable goal. Like most others, I have used the RV's conductive iron frame/chassis as a return current path, provided you have high quality low resistance moisture and oxygen resistant connections. That's where a home designed and built system might (or might not) prove superior to a dealers, since over kill for them (versus ONLY by the book minimums) might reduce their profit margin.

 

Gee its fun and easy to spend other peoples money now lol

 

Best wishes, John T

[oletimer]

^{Thanks to all! Tomorrow I will climb in the under carriage and start tracing wires, then, given our location, try to find maybe a NAPA for some 4/0 welding cable. I think I have enough lugs, and my crimper with me, then reconfigure the ground to a combiner type connection, then to the shunt. I'm also going to install that 4/0 cable for the chassis ground while I'm at it.}

^{Thanks again, and I hope ya all had a Merry Christmas, and now have a Happy New Year. Dick T}

[RBH]

Also check welding supply stores for your 4/0 cable. I found it was the cheapest place per foot especially since shipping all that heavy copper was expensive. I would think NAPA would be a high priced alternative in general.

 

Rich

[Jack Mayer]

Rich has it - get your cable at a welding supply place. It is almost always cheaper. Some of the Home Depots do have 4/0 welding cable, though. But it is rare. Menards carry's it, depending where you are in the country. But you can depend on it being in a welding supply store.

[oletimer]

Well, I thought I knew how to make the TM-2030 read correctly, but, not so. I did change the battery cables so I now have positive at one end and negative at the other end of the bank. I also routed MOST of the negative through the shunt. The reason I say most, is some of the 12V LEDs are grounded directly to the frame. I still thought that would be OK, because the frame ground goes through the shunt on the correct side. All my reading are OK, except the % full (I hope). First thing in the AM, it is showing 66%, but the voltage is 12.6V. We have some sun today, but I wanted to charge with the generator through the inverter (MS-2812), but the charger will not kick in. I think it is because the voltage is now 13.1V, because we're charging @ about 550 watts from the solar, plus at 13.1V it is showing a float charge, but the % full is only @ about 68%. I know the voltage is not really 13.1V, but at rest this AM it was 12.6V. Am I not registering amps somehow? The other night when the voltage was down to 12.5V, I fired the gen, and charged @ 130 amps, which I'm not to crazy about. I did review the settings, because I would rather not charge at that rate, but I didn't think I changed anything yet. All three of the monitors show the voltage within a point or two. How am I wrong??

 

Thanks, Dick T

[SCClockDr]

Well, I thought I knew how to make the TM-2030 read correctly, but, not so. I did change the battery cables so I now have positive at one end and negative at the other end of the bank. I also routed MOST of the negative through the shunt. The reason I say most, is some of the 12V LEDs are grounded directly to the frame. I still thought that would be OK, because the frame ground goes through the shunt on the correct side. All my reading are OK, except the % full (I hope). First thing in the AM, it is showing 66%, but the voltage is 12.6V. We have some sun today, but I wanted to charge with the generator through the inverter (MS-2812), but the charger will not kick in. I think it is because the voltage is now 13.1V, because we're charging @ about 550 watts from the solar, plus at 13.1V it is showing a float charge, but the % full is only @ about 68%. I know the voltage is not really 13.1V, but at rest this AM it was 12.6V. Am I not registering amps somehow? The other night when the voltage was down to 12.5V, I fired the gen, and charged @ 130 amps, which I'm not to crazy about. I did review the settings, because I would rather not charge at that rate, but I didn't think I changed anything yet. All three of the monitors show the voltage within a point or two. How am I wrong??

 

Thanks, Dick T

 

• If the battery Neg is only connected to the shunt then the shunt sees all the amps in & out, individual loads grounded to the frame will still current pass through the shunt.
• The % may be way off till you fully charge and reset the TM-2030.
• AmpHours is a calculated value based on the battery parameters entered, currrent measured in & out, and elapsed time. There are factors that only can be aproximated so the AnpHours will drift off as time elapses.
• The voltage readings while charging are representative of the charging device not the battery. The Battery will return to its SOC voltage after the surface charge is dissipated once the charge current/voltage is removed.

I would isolate your charging devices and see what each does on its own.

if each behaves as expected then look at their interaction.