Need some help with meters...

[gumpy]

Ok, I need some ideas regarding voltage and current meters for general battery monitoring.

My father-in-law has 8 trojan T105s in the trailer he converted and took with us to AK last summer. He parked it last fall and turned off the batteries. Evidently he missed a small load because when he went to get it ready for our camping trip next week he found that the battery pack was really down. Probably well below 50%. He thinks the CO detector was the only thing that was on it, and he didn't think to plug it in periodically. He put a 20 amp charger on the pack and when he didn't see anything happen in the first couple hours, he switched to a 60 amp. After a couple hours of that, and not seeing any results, he figured he'd toasted the pack and went to Sams and bought a new set.

After talking to my battery man, I told him to put the 20 amp charger back on the trojans and charge it at the slow rate for 3-4 days and they should be just fine. So he's trying that now, and they seem to be coming up.

So, now he would like to put some sort of voltage meter in to be able to get a general idea of where the batteries are. Typically, he won't discharge them more than about 80%, but he really has no way of knowing when that is, and doesn't really want to spend $250 on a full blown monitor.

I found some digital LCD panel meters in Jameco.com (pn 108388CJ), but can't tell what I need to do to get these things to just read voltage. I can't tell if I can just hook them up, or if I have to do something else. Has anyone done anything like this in their electrical panel. We just want something simple for now. Basically just a look at the voltage. Maybe eventually a shunt and current meter, too. He doesn't want to spend a bunch of money on meters right now as he just bought the new set of batteries.

Any help or suggestions on cheap panel meters would be appreciated.

And if anyone knows of someone who's interested in a set of 8 slightly used T105s, send them my way    Somebody's going to get a really nice set of slightly used batteries for about half the cost of new ones. Maybe we can find someone building a conversion who's ready for their first set of batteries, or possibly an off grid cabin. They'd be great for that. I've even considered maybe setting up some solar panels and an inverter for a backup power system here at home.

craig

[Moof]

Have you considered an automotive voltmeter?  A simple 2" guage.   It would be inexpensive and easy to mount and make it look nice.

DT

[pvcces]

I would look at a cheap DVM. Theyare available for 5 to 10 dollars, and I think that a good many of them could be run on 12 volts connected to the 9 volt battery connection in the meter. Done right, the meter would still be available for troubleshooting.

Otherwise, maybe Radio Shack, Mouser or Digikey could be some help.

Tom Caffrey
Suncatcher
Ketchikan, Alaska

[boogiethecat]

He'd be better off with a hydrometer than a voltmeter.   Then he can see exactly where the charge state is. They are less than ten bucks and I'd never trust a voltmeter to see what the state of charge is, because it really doesn't tell you....

[DrivingMissLazy]

I heartily agree with this recommendation. Make sure to get the expanded scale where the meter only shows from about 9 volts to about 16 volts. You can get accurate voltage readings with it. At least as accurate as is needed to tell state of charge. Be sure to install an on-off switch for when the unit is in storage or not used for extended periods. I do not think I would want to use a hydrometer daily to check battery status.
Richard

Have you considered an automotive voltmeter?  A simple 2" guage.   It would be inexpensive and easy to mount and make it look nice.

DT

[zxt]

Not entirely sure what you are after, but I would try this meter,
http://www.allelectronics.com/cgi-bin/item/PMD-15V/385/15V_DC_PANEL_METER_.html
or this one if you have to have digital.
http://www.allelectronics.com/cgi-bin/item/PM-21/385/3.5_DIGIT_LCD_PANEL_METER,_20_V_SCALE_.html

If you realy want to use the one from Jameco, you will need to add some scaling resistors like it says in the data sheet, page 2 section 5.
http://jameco.com/wcsstore/Jameco/Products/ProdDS/108388.pdf

[gumpy]

Have you considered an automotive voltmeter?  A simple 2" guage.   It would be inexpensive and easy to mount and make it look nice.

DT

Yes. He said he looked for something at Napa and they didn't have a thing !?!  If he went to the same NAPA I went to one time, I don't doubt it a bit! My experience with one particular NAPA in Pueblo was such that I almost got arrested because of their incompetence and "quality of service".

I think he's looking for something with a little more resolution than the standard automotive voltage gauge. He'd like to be able to discern between maybe tenths of volts. Quarter volts at a minimum.

I did see an analog gauge in the catalog that looked like it had 1/2 volt increments. May look at that again if we can't find anything better.

craig

[gumpy]

I would look at a cheap DVM. Theyare available for 5 to 10 dollars, and I think that a good many of them could be run on 12 volts connected to the 9 volt battery connection in the meter. Done right, the meter would still be available for troubleshooting.

Otherwise, maybe Radio Shack, Mouser or Digikey could be some help.

Tom Caffrey
Suncatcher
Ketchikan, Alaska

This is actually one of the possible solutions we're considering. I bought some cheapo HF meters for like $3 and I put one in the bus to take out there when we go this week. It has a slide switch on it, so we're thinking maybe we just cut the probes off, attach some ring terminals, and hard wire it in the trailer. Leave the dial on 20 VDC, and when we want to look at the voltage of the batteries, slide the switch on.

That may be the best solution we come up with. Cheap and simple.  And oh, did I mention, cheap!! 

Glad to have confirmation of the idea. It means I'm not (the only one who's) loony when I think of these solutions. 

craig

[gumpy]

He'd be better off with a hydrometer than a voltmeter.   Then he can see exactly where the charge state is. They are less than ten bucks and I'd never trust a voltmeter to see what the state of charge is, because it really doesn't tell you....

I don't disagree with you on this, but there are several issues that make this impractical. First, the batteries are burried under the floor of his home built trailer. No bays like on the buses. Second, he's getting on in his years and his knees don't let him access the lower area on a regular basis. He said moving those batteries around once or twice was all he could handle for a day or two. If they were readily available, then it would be the best solution, but under the circumstances, it's just not practical.

All he's really looking for is something that will show a current voltage indication on the pack, just to give him a general idea of the state of charge. At least that way, when he has the trailer stored and passes by, he can do a quick check just to make sure everything as it should be, and when boondocking, can get a general idea of when to start up the generator. 

One other issue with using the hydrometer for daily checking. Acid.  On monday I watered and cleaned all my house batteries and my coach batteries. I was careful. On tuesday, I put the same work pants on that I was wearing. There are now some very odd holes in one of the pants leg. Guess I wasn't careful enough.

[gumpy]

Not entirely sure what you are after, but I would try this meter,
http://www.allelectronics.com/cgi-bin/item/PMD-15V/385/15V_DC_PANEL_METER_.html
or this one if you have to have digital.
http://www.allelectronics.com/cgi-bin/item/PM-21/385/3.5_DIGIT_LCD_PANEL_METER,_20_V_SCALE_.html

If you realy want to use the one from Jameco, you will need to add some scaling resistors like it says in the data sheet, page 2 section 5.
http://jameco.com/wcsstore/Jameco/Products/ProdDS/108388.pdf

Thank you for posting the link to the spec sheet. I hadn't had time to look for it on the Jameco site. This is very helpful.

The two others you posted on allectronics are basically the same as the ones I saw on Jameco. I see there's some notes on the allelectronics site, too.

Thanks. This will help.

[Buffalo SpaceShip]

Hey Craig:

I did a cheap/ simple voltage-check setup for the house batt on the 4106 with parts from that ePlace. See pic below.

I just used a dash gauge voltmeter hooked up to a switch (to keep it from drawing power when off). A momentary switch would be even better so one couldn't leave it on. There might be some better digital voltmeters to be found than the analog I used. There's two Nordskog digital dash meters on the ePlace right now: item #290007212489 and 130007423529. Or one of the meters previously mentioned...

Just some ideas,
Brian

[Burgermeister]

An analog voltmeter is a waste of time to ascertain state of charge through a voltage reading.  In addition, the battery should be rested for 24 hours before even a DVM, accurate to 2 decimal places, can be relied upon to give you a viable reading.

If he wants to rely on the DVOM, split the pack into A and B banks and alternate use by switching. Check voltage only after the appropriate idle time and charge accordingly.

Marc Bourget

[DrivingMissLazy]

I think an analog voltmeter is great for a quick and dirty check on the overall status of the battery which I think he is wanting. Easily read within 1/2 volt and probably closer. And that is close enough for a general check, I think.
Richard

An analog voltmeter is a waste of time to ascertain state of charge through a voltage reading.  In addition, the battery should be rested for 24 hours before even a DVM, accurate to 2 decimal places, can be relied upon to give you a viable reading.

If he wants to rely on the DVOM, split the pack into A and B banks and alternate use by switching. Check voltage only after the appropriate idle time and charge accordingly.

Marc Bourget

[Stan]

Digital meters for the masses are hugely overrated. One would think that nothiing electrical was ever measured before the advent of digital. A high price, calibrated, precision digital meter is more convenient than a high percision analog meter in a temperature controlled oven (even during transportaion from the calibration lab) I have used cheap digital meters that had a 5 volt error at 120 VAC but the owner thought he had 1% accuracy to a deciaml point. Like the advent of digital  watches, it is no longer a quarter past eight but 8:14:52. Anybody can read that on a watch that cost a dollar at Walmart but it may not be the correct time. There is no such a thing as a precision time base in a dollar watch or a ten dollar digital VOM.

If you have need for precise voltage readings, spend a few hundred dollars for something like a higher end Fluke meter or a couple of hundred for a good panel meter.  If you only want to keep records of voltage change without needing to know the exact voltage then a cheap digital will make you happy.

For general information on battery condition, the good quality truck style meters with expanded scale are quite accurate and rugged. Their drawback is the the amount of current they draw, so they should have a switch to turn them on for a reading.

[gumpy]

Stan,

I agree with everything you said.

He has an expensive Fluke meter. He just want's something he can keep track of general voltage ups and downs and use at a glance, rather than pulling out the Fluke. A simple analog meter or a cheapo digital will suffice and it won't matter if it gets banged around a bit. If it's close, that's fine, too, as long as it's somewhat consistent.

We're not doing rocket science here.

The more I think about it, the more I like the cheapo Harbor Freight digital meter with the slide switch on it.

craig