Upgrading batteries and adding battery monitor

[JohnNJean]

If you're an auto mechanic I'm sure you can sort out some of the flaky electrical advice you've been given.

FWIW, I have 2 T105 6V Trojins on my fiver because there is more energy density - more amp-hours - than in 2 12V batteries of a similar size. Buy 'em as a set and replace them as a set. Works for me. YMMV.

There are some slick amp meters available, but I like to keep it simple and just wired in a voltmeter to a light circuit. Tells me everything I need to know. If the reading is 13.2, 13.4 or 13.6, I know what stage my converter is charging. When it gets down to 13.2 I know my batteries are fully charged and I'm operating on shore power. If the voltage is 12.5 I know I'm not on shore power. When this gets down to 12.0 I know I'm at 50% SOC and I need to recharge the batteries.

If I'm on shore power and I see 12 volts, I know a breaker has popped. This has kept me from running my batteries down several times.

Amazon has lots of voltmeter combinations with 12V and USB plugs.

I'm sure someone will point out that the battery has to rest for at least 30 minutes before you get a true reading, but I don't need to split hairs and this tells me what I need to know.

[quicky06]

Originally Posted by RubyDually

Another vote for either a 700 or 702 BMV here...

I just put in a 702 and so far it's the answer to quality battery monitoring.

I went for a 702 because I wanted to monitor the battery temp. Sensor was not included with the 702.

I just ordered the 700 , battery boxes, crimp tool and a couple other odds and ends for the trailer. Will get the batteries and the cable once in know how I'm installing them.

[RubyDually]

Originally Posted by quicky06

I just ordered the 700 , battery boxes, crimp tool and a couple other odds and ends for the trailer. Will get the batteries and the cable once in know how I'm installing them.

Whichever way you go with the upgraded battery bank the monitor will give you a good indication how well your stock converter will handle recharging the new batteries....

So..... your next purchase might be a new converter....

[quicky06]

Originally Posted by RubyDually

Whichever way you go with the upgraded battery bank the monitor will give you a good indication how well your stock converter will handle recharging the new batteries....

So..... your next purchase might be a new converter....

Yea Ive anticipated that. I'm planning on doing my wiring with the intent to upgrade the converter and add sn inverter or two if all goes well.

I'm contemplating moving the batteries toward th back if the trailer, maybe mount them in trays in the side of the frame. It would help me with the weight distribution and length of wire between the converter and the batteries.

Currently the batteries sit on the tongue and the converter is in the back of the trailer. I am assuming that there is a length of undersized cables that runs from the front to the back. So if I can move the batteries to the axle line I will ilimanate a lot of wire and I will just need to have a power run to the jack.

[AB_SP295BHS]

Originally Posted by JohnNJean

There are some slick amp meters available, but I like to keep it simple and just wired in a voltmeter to a light circuit. Tells me everything I need to know. If the reading is 13.2, 13.4 or 13.6, I know what stage my converter is charging. When it gets down to 13.2 I know my batteries are fully charged and I'm operating on shore power. If the voltage is 12.5 I know I'm not on shore power. When this gets down to 12.0 I know I'm at 50% SOC and I need to recharge the batteries.

Once you've run a shunt based battery monitor like the Victron BMV's you'll realize that the voltage method is virtually useless. In an active situation with charging and discharging all the time (even throughout the night) you'll see that the actual state of charge is always less than it appears after a charging cycle and that the draw on the batteries will always make the state of charge look worse than it is. How much better or worse? You'll never know until you try it, I guarantee you it will be a very large surprise.

My experience with a BMV-702 has left me with a very clear conviction that the battery voltage method is nearly useless.

[JohnNJean]

Tell me again what the high dollar meter will do that the voltmeter won't. <G> All I see is amp-hour information and I really don't care about that. I want to know when I'm on shore power and when I'm not. I want to know when my battery is full (12.5v) and when it is at 50% SOC (12.0v).

Perhaps if someone doesn't understand their RV's electrical system, the amp meter might be useful, but for two hundred bucks I think I'll stick to my redneck meter.

Voltmeter $8.90
https://www.amazon.com/dp/B013HZC9TY...ing=UTF8&psc=1

Victron BMV-702 Battery Monitor $203.91
https://www.amazon.com/Victron-BMV-7.../dp/B00MJ85E2U

[AB_SP295BHS]

No problem. The purpose of measuring actual amps in and out of the batteries is to establish an actual State of Charge. IE, if the battery a capacity of 215ah and you draw 43AH the SOC is now 80 percent. In my experience the range of indicated voltage may be from indicated voltages from 12.0 up to 12.4 based upon how rapidly the batteries were drawn upon. No, you haven't drawn your batteries down below 50% and there's no cause for panic to fire the generator up for two hours.

Also, once you've run the generator for a period of time the unit uses a tail current setting that defaults to about 5% of rated AH. At that point the meter resets the 100% bar and synchronizes. This point is now 100% charge. If you, in the above scenario, run your generator for a couple hours is it fully charged? You have no idea because because the only thing the volt meter is telling you is the voltage that the charger is pushing to the batteries, and that voltage is variable based upon the stage of charging that the unit is using. It could be 13.3, 13.7 or 14.2 with my charger, it hints at where the batteries are, IF you understand your chargers different stages. I don't know many people who do.

This is in a simple scenario where you've drawn from fully charged batteries.

I have a large inverter, outdoor AC fridge and sometimes a microwave gets used. After a long night of dealing with crying children the indicated voltage mat be in the mid 11's, yet the state of charge derived from the fully charged reference point and amp meter could be 65%. Do I need to panic and run the generator? Or, do I let the sun rise and forget about it?

At least I have something to work with.

I have four gc2's and am inverting a lot so my examples are more dramatic than a situation where you're only using the DC side of an RV. But I stand by the point that, in either case, the voltage is not indicative of charge without a lot of rest, I think its over 18 hrs with no use. Shut your fridge down, no draws for 18 hrs...it isn't practical.

If you are using your batteries very lightly and are watching like a hawk your method may help you, but how much longer are you listening to your generator than necessary? Are your batteries fully charged? It affects their lifespan.

I've seen BMV 700's for a hundred bucks or so on ebay, I think it will extend my batteries life and quiet my campground through a better understanding of what's going on. If you're cash limited it may make sense to extend the life of your batteries.

I installed a bmv-702 so I can read temperature and the temperature function hasn't proved useful, they don't seem to heat up much if at all in my system. It may be different in other setups, but sticking to the bmv-700 can save some bucks.

[JohnNJean]

You make the case for these amp-hour meters very well for use in more complicated systems where your batteries never get completely unloaded.

My battery voltage is stable within about 30 minutes, but I have a pretty good idea where my batteries are just from experience. My concern is keeping them >50% - I'm not that worried about getting that last five percent in them. I don't need a meter to tell me when my tanks are full, either.

The two hundred bucks I save on the meter will buy me a couple of replacement T105's, but I expect to get many more years service from the existing batteries.

[FFred]

"I'm not that worried about getting that last five percent in them."

You should be as when not charged to 100% + the batt service life will be shortened .

Weather they last 4 years or 8 years is determined by the depth and number of discharges , and weather they get FULLY charged.

[babock]

I will personally probably get a battery monitor but for the main reason is that I like gadgets. A battery voltage gauge will likely be fine for 90% of RV owners that actually camp with out hookups.

[JohnNJean]

Originally Posted by FFred

"I'm not that worried about getting that last five percent in them."

You should be as when not charged to 100% + the batt service life will be shortened .

Weather they last 4 years or 8 years is determined by the depth and number of discharges , and weather they get FULLY charged.

Certainly a consideration with some types of batteries, but memory effect is negligible with lead acid batteries. More important to avoid sulfation.

[quicky06]

The way I looked at it was a volt meter would get me by with no idea how the charger is doing.

Having a battery percent with an alarm garentees I know where my batteries are at and I will be warned I don't notice it is low.

Looking st the battery charging voltage only tells
Me that the charge is charging but not much more. Being able to see how much amperage is is going in and out. I can monitor if the charger is working properly not just if it's supplying 5 amps.

[banda]

These two monitors seem to do pretty much the same thing, but there is quite a price difference. Am I missing something?

https://smile.amazon.com/Victron-BMV...ywords=bmv-700

https://smile.amazon.com/gp/product/...f_rd_i=desktop

[quicky06]

Originally Posted by banda

These two monitors seem to do pretty much the same thing, but there is quite a price difference. Am I missing something?

https://smile.amazon.com/Victron-BMV...ywords=bmv-700

https://smile.amazon.com/gp/product/...f_rd_i=desktop

The 700 is what I ordered. The only difference between the 700 and 702 that I found is the 702 includes a battery temp reading which I don't need.

The second one you listed: I don't like the interface, it's too busy. The unit does not advertise any alarm functions ( such as setting an alarm at 50 percent battery soc). It also uses a USB cable for the sensor and the other unit uses a phone cable.

If I leave the batteries in their current location I would need a 30 plus foot USB cable and would be governed by factory USB lengths. Using a phone line I can run the line through smaller holes and keep it one piece with no splices

[Granny K]

What an interesting and informative thread!
My 2017 Forester 2391TS has one RELiON RB100 100AH 12V Lithium Ion battery (installed by FR at the factory) and I have purchased a second identical battery to give me 200AH (DH has a CPAP machine).
Can I install the second battery without upgrading the converter? Should I consider upgrading the converter and are there any other issues I should be aware of.
PS: battery monitor sounds like a great idea!

[AB_SP295BHS]

Originally Posted by banda

These two monitors seem to do pretty much the same thing, but there is quite a price difference. Am I missing something?

https://smile.amazon.com/Victron-BMV...ywords=bmv-700

https://smile.amazon.com/gp/product/...f_rd_i=desktop

Could be a good find, I don't know anything about the cheaper unit. If it has a shunt, which this one does, it has the capability to do what the Victron one does. Just need to dig through the capabilities.

Cheaper than Amazon...as usual...
Victron Energy BMV700 Precision Battery Monitor | eBay

[AB_SP295BHS]

Originally Posted by Granny K

What an interesting and informative thread!
My 2017 Forester 2391TS has one RELiON RB100 100AH 12V Lithium Ion battery (installed by FR at the factory) and I have purchased a second identical battery to give me 200AH (DH has a CPAP machine).
Can I install the second battery without upgrading the converter? Should I consider upgrading the converter and are there any other issues I should be aware of.
PS: battery monitor sounds like a great idea!

You don't need to do anything other than buying an additional battery box and understanding the difference between wiring batteries in serial and parallel.

[babock]

Originally Posted by AB_SP295BHS

Cheaper than Amazon...as usual...
Victron Energy BMV700 Precision Battery Monitor | eBay

Not enough discount. I like to be able to send things back if they don't work and Amazon is great with returns.

This one is from a more volume dealer and is cheaper. It might be a possibility for me.
http://www.ebay.com/itm/Victron-BMV-...BX~r4t&vxp=mtr

[babock]

I do like the Bluetooth dongle and be able to see the state on my phone.

Victron VE.Direct Bluetooth Dongle for Battery Monitors and MPPT Controllers | eBay

Did I say earlier I like gadgets?

[banda]

Originally Posted by quicky06

The 700 is what I ordered. The only difference between the 700 and 702 that I found is the 702 includes a battery temp reading which I don't need.

The second one you listed: I don't like the interface, it's too busy. The unit does not advertise any alarm functions ( such as setting an alarm at 50 percent battery soc). It also uses a USB cable for the sensor and the other unit uses a phone cable.

If I leave the batteries in their current location I would need a 30 plus foot USB cable and would be governed by factory USB lengths. Using a phone line I can run the line through smaller holes and keep it one piece with no splices

You're right about the alarm. The DROK does not appear to have that. I think the display is a matter of personal preference. The DROK shows multiple parameters at once in small numbers, while the Victron shows single parameters with larger numbers. As for the cables, the DROK does offer wireless data transmission up to 10 meters, so at that distance no wires are required. It also has over-current protection, overvoltage protection,
under-voltage protection and time-limited protection.

Just like most products, it is difficult to find all the features you want all in one unit, but I think both are viable options, as is the Trimetric unit. (Although pricier.)