Battery Monitor Help

[Paul & Deb]

So, i just returned from a 4 day camping trip on the beach with no hook-ups. I had an up and down experience with my power so I really want to monitor my usage better.

I currently just have the factory "idiot" light state of charge monitor in the control panel. I think I need to have more information so I am looking at 2 different systems and am open to other suggestions.

http://shop.pkys.com/Victron-Energy-BMV700-Precision-Battery-Monitor_p_2810.html

http://www.solar-electric.com/batteries-meters-accessories/metersmonitors/tr20mosy/trtmbamosy1.html

 

[Cate&Rob]

Hi Paul,

I have the Victron monitor on my boat. The boat is much more like your "dry camping" usage (as compared to my nearly always plugged in 303 RV) with an Onan generator and multiple battery bank. Once programmed with the parameters of the battery bank, the Victron gauge is a very reliable monitor of amp hours in and out. I have no knowledge of the monitor in your other link, but it looks like it might be similar. Victron is a premium brand in the marine industry . . . they make good stuff. They are based in the Netherlands.

Rob

 

[KeithS]

This is always a good review: http://www.marxrv.com/12volt/12volt.htm (The 12 volt side of life).

With an inexpensive ammeter, you can check/monitor the battery state of charge.

 

[Cate&Rob]

With an inexpensive ammeter, you can check/monitor the battery state of charge.

Hi KeithS,

That looks like an interesting link . . . but a long read . . .I will get back to it .
The value of the Victron (or similar) monitor is that it totals up amp hours in and out of the battery bank.
It is also an ammeter and a volt meter for instantaneous readouts, but what is important is how much you have taken out of (or put back into) the battery bank over time. The amp hr capacity of a battery (or a bank of batteries) is often mis-understood. For a stable system, you should be able to live within 30% of the stated capacity. This is because it takes a long time to charge beyond 80% (the bulk charge max) and discharging to less than 50% will damage the battery.

Rob

 

[Paul & Deb]

Hi Paul,

I have the Victron monitor on my boat. The boat is much more like your "dry camping" usage (as compared to my nearly always plugged in 303 RV) with an Onan generator and multiple battery bank. Once programmed with the parameters of the battery bank, the Victron gauge is a very reliable monitor of amp hours in and out. I have no knowledge of the monitor in your other link, but it looks like it might be similar. Victron is a premium brand in the marine industry . . . they make good stuff. They are based in the Netherlands.

Rob

I was hoping you would chime in Rob. I found a post of yours in an earlier discussion and you provided a link but it was no longer valid but after a little checking I thought the Victron was the one you were referring to. It isn't as expensive as I anticipated which is good.

 

[Soldotnatom]

I use and find the Trimetric to work well, but if I want to get the most accuracy with it there are more settings than I use. I set the parameters for basic monitoring and that lets me make much better decision making on usage and charging. Changing batteries requires setting the parameters again, so keep theTrimetric instructions handy.

Another possibilty is the Smartgauge. It is a United Kingdom product and harder to find. It is also more expensive. It sounds interesting because of it's simplicity of installation and setup. If the manufacturer information is accurate it will eliminate all the settings I currently have to make with my Trimetric except battery type. The site is Smartgauge.co.uk , it seems to be sold as the Balmar Smartgauge in the United States.

Maybe someone on the forum has experience with it and can give real world use information.

 

[J&G garage]

I used a Xantrex monitor on my boat at about three times the cost of the Victron unit (must be 3 times better right?).

I was going to put one in the trailer too but I like the price of the Victron. They both do the same thing. In any case your are flying blind if you don't have a battery monitor other than the LEDs that come with the trailers.

 

[Paul & Deb]

Thanks guys. I'm really interested in the Victron I think but one thing has me a little stumped. When you initially install it you go through just a couple steps to kind of synchronize it. For instance it has to be set to know the battery or batteries available amp hours. In doing so they recommend starting off with new batteries! I certainly don't want to buy new batteries. My Trojans are only about 1 1/2 old. It apparently reads the voltage but not amp hours and another parameter. Do you really think I need to install new batteries just for this to work accurately?

I think I will contact the retailer on Monday to ask but since you have one of these in your boat rob, I thought I would ask.

One of my problems on this trip was partly my fault but another was that I didn't realize how much of a drain running the heater was. Our first night on the beach was pretty chilly so Deb turned the heater on in the early afternoon and just left it running. Then in the evening we turned on our inverter to watch some TV and within an hour or so the battery was kaput. One step, when running my inverter setup, that I forgot is that my refrigerator is on one of the 2 circuits with my inverter and, when in use, I need to force the fridge to LP. Well, I didn't and between the heater and the fridge, I was out of battery in short order.

I now have a big label next to my inverter switch reminding me to ensure the fridge is on gas. Over the next few days we got into a pretty good routine with the generator charging and running the evening dinner process and warming the rig up and then shutting it down for the inverter to run our entertainment system at night.

What I don't have any good sense of is how much the batteries drain during this usage and how much they recharge. I'm hoping a good meter like this could provide me that information so I will have a better understanding of what we can and can't do withing the limits of our setup.

 

[Cate&Rob]

Hi Paul,

You certainly don't need new batteries ! I think they are only trying to tell you that batteries lose some of their theoretical amp hour capacity as they age. I set mine at slightly less than theoretical, just for this reason. This only comes into play for the % state of charge display, which is just adding or subtracting what you have added/used to the theoretical number you provided. I usually pay more attention to the readout of actual amp hours used/replaced. If (when) a battery begins to go bad, the % calculation will start to make no sense, but the actual amp hours will be correct.

This monitor will show you a lot about your system. One of the interesting things is charge rate. When significantly discharged the batteries will accept the rated output of the converter. When you get up around 80% state of charge, the batteries will only accept a fraction of this. This is where it takes a lot of generator hours to get to 100%.

The installation is really straightforward, with only the gauge and the shunt to install. Communication between the two is a standard plug-in telephone wire. My boat system has been in place for about 6 years.

Rob

 

[Paul & Deb]

Thanks so much for that input Rob. I think I will go ahead and order it. It comes with a 500 amp shunt and about 32 ft of wire, which should be plenty.

I am really interested in learning how long it takes to recharge the batteries with the generator because mine uses about 1 gallon of propane per operating hour and i was running it for 3 or 4 hours a night. I don't mind doing that, it's only money , but I want to make sure I am recharging enough and yet not running it longer than I need to.

 

[J&G garage]

+1 on the new batteries. You're fine. I think you'll find that after using a quality battery monitor for a while you'll get to know your batteries and how long you can go before recharging. My wife used to give me a hard time because the first year I had the Xantrex monitor I was checking it constantly. After a while you'll know you can go 3 day or what ever with your setup and you'll check it less often. One neat feature of a monitor is you can do an energy audit on all your 12vdc components by simply turning on each item one at a time and reading the current draw on your montior. In doing this you know how many amp/hrs each is using and then things like the furnace fan can't sneak up on you.

 

[Paul & Deb]

That's me too Jim. I'm constantly checking the factory monitor and Deb is always asking me what I'm doing. And the energy audit is exactly what I need.

 

[Soldotnatom]

Hi Poppy,
I know what you mean about the furnace. When I installed my trimetric It showed the furnace drew over 12 amps, not the 8 max the manufacturer says. I realized why the batteries ran down so quickly. The meter will really help you locate power draws.

 

[Paul & Deb]

Hi Poppy,
I know what you mean about the furnace. When I installed my trimetric It showed the furnace drew over 12 amps, not the 8 max the manufacturer says. I realized why the batteries ran down so quickly. The meter will really help you locate power draws.

See I need to understand what that means in relationship to battery draw. Does that mean 12 amps per hour? Don't my 2 Trojan 105s give me 450 amp hours of service? I need to learn what all that means to me.

Sent from my SM-G900V using Tapatalk

 

[Cate&Rob]

Hey Paul,

Lets do some “electrical” math . . .

Starting with that 450 Ah bank, if you are charging by running the generator for a reasonable length of time, it will be difficult to get past 80% (12.5V).
So, 360 Ah is “available”. But, you risk damage to the batteries if you discharge them below 50% (12.2V). In fact, most inverters will shut themselves off at 12.2V to prevent battery damage. Thus, when you should stop drawing from the batteries, you still have a “theoretical” 225 Ah left . . . if you were to draw the batteries absolutely flat (11.8V). The safe range is 360 - 225 = 135 Ah for a 450 Ah bank.

Let’s say that furnace is running 1/3 of the time and drawing 12 A when running. 24 hrs x .33 x 12 A = 95 Ah per day. The fridge and water heater control circuits plus lighting might quite likely use up the other 40 Ah in 24 hours . . . meaning that you can use the furnace (on a 33% duty cycle) for one day without recharging.
If you are using the inverter to run 120VAC devices, this will draw down the bank much faster. For example, 2A at 120 VAC is 20A at 12VDC. (actually more than 20A because of inverter inefficiency)

The above is all just “theoretical calculation". The battery monitor will tell you the exact details of your usage but this info will likely be similar to this model. The important part is that you should strive to live within a 135 Ah discharge/ recharge cycle with a 450 Ah bank.

Rob

 

[Paul & Deb]

Wow, that's a great, understandable description of what's going on for me Rob. It really helps but it also disappoints me. The realization that you spend all that money on batteries and they're really only good for 1/3 of their "capacity"!? That's kind of crazy for me to realize. I will be very eager to learn more about my capacities and usage when I get my monitor set up.

I am also extremely eager to learn how long it takes to recharge the batteries with the generator. I know one thing now for certain, the Onan LP generator is a fuel hog! I didn't pay close enough attention (I will next time I dry camp) but I think it sucks down about 1 to 1/12 gallons of propane an hour. I might regret selling my pair of Hondas for use on longer dry camping outings but that's water under the bridge now.

I also wish my front compartment was large enough to hold another pair of Trojans. That would help at a reasonable expense. I think I did see a photo on the internet of a 337 with 4 Trojans mounted along the front wall in the pass through. That's a thought which would also open some space up in the front storage compartment. Just a thought.

We only dry camp a few weeks a year but when we do, we want to stay spoiled in our trailer so ample power is important.

 

[Paul & Deb]

I did some searching and I found the picture I was referring to. Looks like a clean job but this would get me a lot more storage capacity.

 

[J&G garage]

Poppy it's not that you only get 1/3 the capacity that you paid for it's that charging to full capacity can take a while. Charge more often or longer to get your capacity back or look into solar panels (although they are pricey). My boat also had 4 T-105s. I used about 70 amp/hrs/day to run the 12 vdc refrigeration. Charging with a 120 amp alternator on the engine every day after the first day would get them to about 85 to 90 percent. If I had kept the boat I would have gone solar. It really seems to add "capacity".

 

[Paul & Deb]

Poppy it's not that you only get 1/3 the capacity that you paid for it's that charging to full capacity can take a while. Charge more often or longer to get your capacity back or look into solar panels (although they are pricey). My boat also had 4 T-105s. I used about 70 amp/hrs/day to run the 12 vdc refrigeration. Charging with a 120 amp alternator on the engine every day after the first day would get them to about 85 to 90 percent. If I had kept the boat I would have gone solar. It really seems to add "capacity".

I've thought about solar but I can't justify the cost for the amount we would use it. I'm comfortable knowing I have to run the generator to recharge, I just need to get a better handle on how often and how long I need to run it.

If I went with another pair of batteries do you know which is the most efficient way to use them? Before I went with GC batteries I had 2 - 12 volt batteries and I had a selector switch so I could run "1. #2 or both. I guess I would do the same? Do you know if the system can be set up so you use one set and then when they need to be recharged you select the other and then charge the set that is down? I don't know how you would isolate one bank over the other for charging. That's probably not possible.

Since I'm taking about this as even a possibility I guess I need to buy the model of the Monitor that allows monitoring of two different banks. It's about $50 more but would be worth it.

 

[Cate&Rob]

Hi Paul,

Unless Victron has upgraded the functionality of this latest monitor, the monitoring of a second bank is only very basic. The original idea from the marine application, is to fully monitor the "house" bank and just keep an eye on state of charge of the "starting" battery (by way of accurate voltage measurements . . . I think).

In your original message, I thought you meant "furnace" when you said heater. If you were running an electric heater through the inverter, from the batteries, this would use up your battery capacity in two hrs, even on low. Low would likely be 750 watts, which is over 60 amps at 12V . . . so about 2 hrs.

Even an entertainment system that might draw 3 amps at 120VAC is significant to a 12VDC battery. This would be more than a 30 amp draw from the batteries.

Rob