Battery Monitors

[Lucky Dog]

Some what off course... but figure there would be lots of suggestions?

Even though it is -7c outside we are thinking of the spring. In Minnesota we have solar powered regatta fro schools. Trying to have some fun and learn about solar power. We also host the largest high mileage vehicle(?) race for schools in the country. These a based on a 3.5 B&G gas engine (huge supporters). We have several schools wanting to experiment with electric vehicles. They called me today to fine out what to use to measure battery drain in 3 laps around a race track.

Cost being an issue for school, in case you haven't heard.

The is no need to monitor charging from race committees point of view.

Any ideas or links or plans would be great.

PS I have shoveled the snow from our boat 5 times now.

 

[Mark F]

Hi Lucky Dog,

That's very cool that the school is working with electric propulsion. They might be able to use one or more of these;

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10080

The price is certainly right.

It just so happens, I received one in the mail today. I have not used it yet so I can't vouch for it's effectiveness. I did find some info on it on an electric vehicle web forum. People are using them for electric scooters, bikes and boats. The watt meter is made for RC models but it's rated to 60 volts and 130 amps.

The electric inboard on my boat is 48 volts and the highest current I draw is around 100 amps. I got it to experiment with an amp readout at the helm. If nothing else the entertainment value will be worth the $29!

 

[Maine Sail]

You'll likely want a battery monitor. Xantrex, Victron, Ample Power, BEP, Blue Seas and others all make them.

The monitor will need to be carefully programmed to the bank of batteries to measure the state of charge. As batteries do not always drain at the same rate, or at the stated 20 hour rated value, when different loads are imposed, using the SOC or % state of charge screen on most monitors will give you the most accurate level of charge. On most monitors this screen takes Pukert effect into account where the Ah screen does not.

If a 100 Ah battery is drained at a 5 amp load you would ideally get 100 Ah out of it. This is or would be the the batteries 20 hour Ah rating. If however that same battery was drained at a 30 amp load you would not get anywhere near 100 Ah's out of it. A 30 amp load for an hour could deplete the bank by considerably more than the 30 Ah's shown on the Ah screen due to Peukert's Law.

This is where the Peukert's law comes into play and why the SOC screen, in a situation with high amp draw, would be the better screen to use than the Ah screen for monitoring state of charge.

Said more simply as the rate of current/amperes drawn from a lead acid battery increases, the available Ah capacity decreases. This is why counting only the Ah's in high draw situations can leave you well off your mark.

A Victron BMV-600 would be a good reasonably priced monitor at $158.10 from Jamestown Distributors. I have installed a number of them and not had a problem. Tom Metzger on the other hand has had some accuracy errors with his BMV-602, a two bank version of the BMV-600, in terms of bank 1 voltage being slightly off the reading of bank 2 by .02-.03V if I recall correctly.

 

[Guy Stevens]

QST magazine

QST (Ham Radio) magazine had a build your own amp hour meter article about 8 months ago? (Guessing). It was a great and simple little project. It was based as I remember on a inexpensive programmable controller, I think the whole cost of the project was less than $20.00. The authors code with good comments was available along with the design.

Guy

 

[paul culver]

Hey Mark F

Its been a while since you last posted on your inboard electric install. Any updates? Do you have a better idea of what the regeneration capability is?

Thanks

Paul
E29 "Bear"

 

[Tom Metzger]

I like Mark's suggestion. You don't need a fancy monitor to read battery load unless you you are interested in recharging, which apparently you are not. Watt-hours should be enough.

That said, the range on this meter is not very high so you would want to make sure that your cars operate in the same range.

I wouldn't use it on a boat's propulsion motor with these limitations. Also, there is no shunt so all of the current has to go through the meter.

YMMV

 

[Mark F]

Guy,

I like your suggestion about having the kids make the meter. It would be another layer of understanding. Wish I knew more about this stuff.

Paul,

I haven't done much in the way of monitoring regeneration in the past couple of months. The monitor, a PakTrakr is down below so it takes effort to watch the amp readout. That is one of the reasons I'm looking to setup the Turnigy Watt Meter at the helm. I'll post something soon about my experience with the EP to date, a preview is that it's all good .

Tom,

The Watt Meter does have a shunt. I'm in the process of learning how to remove it from the unit so I can mount it remotely and not have to run heavy gauge wire to the helm. It's been done and works. Regarding the limitations of the meter for my use, it should work ok. The meter is rated to 60 volts and 130 amps so it's within my system's upper range. All that said it's an inexpensive little unit and worth it to me for experimentation.

 

[Lucky Dog]

Thanks for some of ideas.

I am trying to find the article that Guy referred to.

These are last years boats the students built including the electric outboard