House battery(ies) monitor

Ferg · Posted: Thu Jul 07, 2016 3:29 pm Post subject: House battery(ies) monitor

I'm in the process of replacing my deep cycle house batteries (total 180ah) and hoping someone in our group could recommend a permanently mounted amp hour meter

Sunbeam · Posted: Thu Jul 07, 2016 4:58 pm Post subject:

I can recommend a couple (but there are many good ones). First thing is that there are two different types.

One is a coulomb (amp) counter type. Of those I like the Victron BMV-700 or BMV-702 (702 can either monitor voltage for a second bank or keep track of temp). These are excellent for seeing what things draw (although of course once you know that once, it doesn't really change) and for keeping track of amps in and out. They give you a SOC (state of charge) in percent, but it can be subject to some inaccuracies. You can take steps to mitigate those (set bank size; drop size down as batteries age; disable or set certain parameters certain ways such as no auto 100% feature). This type requires a shunt to be placed in the negative line just as it comes off the house battery. Not that that's a big deal.

Type two works via algorithm. For example, Smart Gauge. This gives you a really accurate SOC (and voltage) but doesn't show you how many amps things use. It's basically a "SOC meter." Super easy installation (two small wires to battery posts) and no calibrating as battery bank size ages smaller.

I have one of each because I'm a nerd who likes data, and because their differences complement each other .

For pure SOC use, I prefer the Smart Gauge. For a great combo I like both. If someone only wants to buy one? Hmm, that's a tough one! Either is way better than nothing though, so you can't totally go wrong. I guess I'd have to take the Smart Gauge if I could only have one (but luckily there is no such rule Very Happy

)

If you want to read more detail on them (with lots of photos) --- both for installation/setting up of Victron, and for Smart Gauge -- then Maine Sail has a few good articles at the following links. Of course there are also a great many knowledgeable people here - but in case you are interested in more reading:

Installing battery monitor (Victron amp counter type):

http://www.pbase.com/mainecruising/battery_monitor

Keeping above type more accurate:

http://www.pbase.com/mainecruising/programming_a_battery_monitor

More about algorithm type (Smart Gauge):

http://www.pbase.com/mainecruising/smart_gauge

Ferg · Posted: Thu Jul 07, 2016 5:38 pm Post subject:

Sunbeam, thanks a million

Your post nailed it! I wasn't even sure what I was looking for; now I know the SOC is exactly what I wanted.

SmartGauge is ~$290 on Amazon, a bit pricey, but I'll start value engineering and see where I land.

Thanks again,
Ferg

thataway · Posted: Thu Jul 07, 2016 5:46 pm Post subject:

Specifically what batteries do you have now, and what are you replacing them with? What is the intended use of the batteries: For example, run refer 24/7 when cruising a month at a time, one day a week under way? Vs an occasion overnighter? How are you gong to be charing them? Shore, high capacity battery charger, outboard (output of our alternator).

How long did the old batteries last? Were they ever discharged more than 50%? (by less than 122 volt criteria at rest?

The options that Sunbeam suggested cover the ones often used. There are far cheaper versions, which have some negatives.

I do suggest that you might consider Group 31 batteries, vs group 27 which you probably have now. If you have higher loads, then there are even further options.

Ferg · Posted: Thu Jul 07, 2016 6:10 pm Post subject:

Dr. Bob,

Don't know how long the prior batteries lasted, I bought her last year, and they were on their last legs. I'm guessing they were originals on my '08. Also they were dual starting/deep cycle.

I already bought two Group 27/90ah deep cycle, so so much for the larger ones.

We generally cruise, and really don't plan on using the heck out of the batteries. We will probably anchor out 3 days/summer month. I only need it to drive the microwave, tv, fridge, stereo and charge the Bluetooth speaker. With the exception of the fridge, there will be infrequent use of the others.

We keep the boat on a trailer at the house, so it's always smart-charged, plus we have a Honda 2000 on board. I just like to enjoy the quiet when I'm on the hook

Sunbeam · Posted: Thu Jul 07, 2016 6:50 pm Post subject: Re: House battery(ies) monitor

Good point on checking the type of batteries. For example, the Smart Gauge can't work with lithium batteries, because it relies on reading voltage. I assumed (not the best method!) that if a person were putting in lithium batteries they'd mention it, since they are still rather special. I figured flooded cell or AGM most likely (but should have asked).

Ferg: Your "only three days at anchor using microwave, fridge, TV, and stereo" would be maxing things out for me. That's a fair load (especially with the inverter/microwave which really hits the batteries) so I think you are smart to monitor SOC in some way. It doesn't take too many sets of batteries (less than one in some cases) to easily pay for a Victron (or similar) or SmartGauge. I had a friend a couple of years ago who went through many (!) sets of batteries at over $1000 a pop (set) before getting his Victron set up correctly and adding a SmartGauge. Of course it's not so dramatic if you are talking about a couple of $100 batteries, so maybe harder to justify. So of course there is no one right answer for everyone.

thataway · Posted: Fri Jul 08, 2016 1:07 am Post subject:

In small boats where I have had a microwave I have dedicated batteries to the inverter, or very robust batteries. For example, I probably would want over 90 amp hours dedicated to the microwave. (depending on use). The inverter will probably draw 100 amps when running the microwave.

You have 90 amp hours "usable". Depending on the ambient temp, you are going to be pushing the reserve with the refrigerator alone, if you don't charge batteries every day. I probably would add a 3rd 90 amp hr group 27 to your bank, especially in a 2008 25, where there is plenty of room for the extra battery. Use the two group 27 in parallel as the "house bank" and monitor these. Keep the other group 27 as a starting battery. Add a VSR to charge the "house bank" or if your motor has a second charing circuit use that for the "house bank".

Then using the Victron or similar monitor (I use a Link--same idea), you will have a good handle on when you need to charge the batteries.

Unfortunately the battery charger which comes with the boats is fine for topping off the bank at home or at the dock, but not for charging the batteries from the Honda EU 2000. I carry a 30 amp marine charger just for the refer battery, and then use my upgraded Mastervolt battery charger for the other batteries.

Ferg · Posted: Fri Jul 08, 2016 12:06 pm Post subject:

Actually I do have two paralleled 90ah hours hoise batteries along with a separate starting battery.

I'm not sure if I have the original charger; it currently has a Guest 20 amp duel (5,5,10).

Dr. Bob, can you why the Honda 2000 won't be sufficient to charge. This is out of my area of expertise (that makes it sound like I actually have an area of expertise)

journey on · Posted: Fri Jul 08, 2016 3:28 pm Post subject:

Well, Dr. Bob didn't say that the Honda 2000 wouldn't charge your batteries. He did say that your battery charger isn't adequate.

The Honda just supplies 110 vac, up to 1800 watts which is more that adequate for the job. The battery charger turns it into the required DC and supplies it to the batteries.

There was a thread about the lack of performance of the small OEM charger and with what we replaced it.

Boris

thataway · Posted: Fri Jul 08, 2016 6:10 pm Post subject:

The Honda EU 2000 only puts out about 8 amps with its 12 volt battery charging circuit. The "factory charger" which you have will not charge the batteries rapidly. It will be limited to 5 amps to each of the two "house" batteries.

I have a separate 30 amp charger (runs off a Honda EU 1000) which I run for a little less than 2 hours to bring two Group 31 batteries up after running two chest refer/freezers. You can certainly put in 20 amps--and probably 30 amps into the two 90 amp batteries you have. Good to know that you have the two battery house bank! With the monitor you can watch the voltage and SOC.. If you wanted to use the 12 volt circuit from the Honda, it would take about 12 to 15 hours to come up to full state of charge. Charge tapers off as it reaches the "float stage" The last 10% of charge takes a long time,

ssobol · Posted: Fri Jul 08, 2016 11:34 pm Post subject:

My engine alternator (Honda BF90) will put a lot more amps into the battery than my Honda 1000 will through the battery charger. The generator charging is limited by the battery charger current (in my case 5 amps/channel).

However, even when the battery charging is not limited by the charger, I think that engine powered battery charging is more efficient. A Honda 2000 will only give you about 18 amps to a single battery if your charger is single channel and the current is not limited by the charger. A dual channel charger will only give you half that, and AFAIK dual channel chargers do not combine currents from the other channel if one battery is already charged.

thataway · Posted: Sat Jul 09, 2016 1:27 am Post subject:

ssobol · Posted: Sat Jul 09, 2016 11:24 am Post subject:

By my calculations a Honda 2000 at 120v gives you 15 amps output (at the full 2000 watts). With the right charger you could get about 40 amps output to the battery with this input. In this example, a Honda 1000 might give you 20 amps charging current.

With my Guest 20 amp 3 bank charger, the input current at 120v is 5a max. The output is 5/5/10a at 12V. This charger does not automatically combine outputs to supply max available current to a single channel. You can combine outputs via the wiring, but this is not dynamic.

Apparently in my setup I can get 5 amps max into one battery and 15a max into the other one (two channels in parallel).

My BF90D will put about 28.5 amps into the battery at anything >1000 rpm. At idle it is ~17 amps (for a battery at 70% charge) according to the Victron battery monitor.

It would seem that the battery charging on my boat is limited by the charger more than the available input energy.

thataway · Posted: Sat Jul 09, 2016 7:03 pm Post subject:

As per Honda EU 2000i Specs:

journey on · Posted: Sun Jul 10, 2016 12:31 am Post subject:

Hello!!!!

Will everyone start labeling their outputs as charger or generator? And use the terms AC or DC?

Bob's correct on what the Honda generators are putting out and that's AC

One can get 40 amp DC @ 13.5 volts DC out of a battery charger (13.5x40=540 watts DC) if one puts 4.5 amps AC at 120 volts ACx2 (960 watts AC) in from the generator. The factor of 2 is used because the charger is less than 50% efficient.

What's not mentioned is that with flooded lead-acid batteries the charge rate goes down rapidly once charge is started. That 40 amps DC will soon drop quite significantly to 20 A DC, then to 10 amp DC, etc.

And finally, here's a discussion on the Guest Charger.

Boris