Why MHs should have Digital Voltmeter's in the Cab

Dozer Dave

I sold my last motorhome years ago but it had 2 batteries, main engine battery and leisure battery. Which battery do you want to a voltmeter on as your post contains observations from both?

Linking two batteries makes one bigger battery so by deduction you can observe the aux. batteries from the engine battery.

Monitoring the engine battery in the cab would be all that's needed there.

In the living quarters I have a much more accurate and sophisticated battery monitor which watches split bank voltage, and single bank current and DOD. I also have two DMMs as well as a current and voltage readout on a PSU I use to charge from mains.

I spent years full time without a decent meter and yeah stuff works but you'd be amazed how much you can improve a system once you know what's going on, and further amazed at how woefully inadequate some manufacturers promises of battery maintenance are fulfilled by their products.

Dozer Dave

Dozer Dave wrote: »

Which battery do you want to a voltmeter on as your post contains observations from both?

The same gauge can do both with an upstream series SPDT switch switching positives B1+ and B2+.

Of course it'll read the same if your batteries are paralleled.

Dozer Dave

Sir Liamalot wrote: »

Linking two batteries makes one bigger battery so by deduction you can observe the aux. batteries from the engine battery.

The motor home I had they were seperate, my leisure battery was the sole battery for the home. Is yours different?

I've a set of 2 x 6Vs in series for the house bank and an overspec-ed el-cheapo starter battery. They're usually isolated.

I've a manual switch activated relay to divert the alternator -> starter battery -> solar controller -> house bank.
A manual 20A switch (needs upgrading soon) on a battery to battery conductor.
and an intelligent voltage sensing split charge relay that needs a few minor modifications.



...since that I've swapped the traffo for a current limited PSU and added this..



Here's the full scéal sorry, bit longwinded...I keep changing things, almost finished now :pac:

Dozer Dave

Ok take my old motorhome, what battery should i have had the voltmeter on?

Engine battery voltmeter in the cab. For driving related info.
(add a switch and a wire it can do both battery sets)

Decent battery monitor in the living compartment monitoring auxiliary batteries and with an engine voltmeter readout.


Digital readout, 3 digit display, 4 digit resolution. ± 0.3% accuracy, low noise on dedicated conductors.
Analogue is too vague and those green for good red for bad are libelously optimistic and a compete waste of time and batteries.

..would be my recommendation.

Dozer Dave

So the voltmeter in the cab is for the engine electrics, what is so unreliable here for a volt meter?

It's just a tool that gives useful information.
I don't expect my temperature gauge to do a whole lot either but I wouldn't sacrifice it.

Dozer Dave

But you have said in opening posts you have regular alternator failure and no disrespect but is this due to your aftermarket wiring?

Partly but not wholly. Alternators are dumb. It just sees my wiring as a big load buffered by lots of batteries.
My stock alternator is under-rated and underwired for the max. load I can put on it. I usually limit it.
I go through a set of brushes a year and I'm suspicious the commutator axis is less than true after 190 000 miles and umpteen idling.
This combined with heavy loading mills through them but they're nothing parts and I always have a pre-loaded set on stand-by.
I change the regulators seasonally as a means of temperature compensated charging.
Slip rings wear as do bearings.

Recent failure with brushes popping out of the holder was my fault; I set the travel distance too long soldering them in.

Over-voltage; no idea, could be dodgey zeners (all rectifier diodes are zeners) could be after market regulators (3 in a row) could be alternators need some load.

Dozer Dave

If alternators are dumb why don't you invent your own?

Already been invented.

I look at a thing and see input energy (Diesel) versus output (charge in batteries) with a round trip efficiency ~16% (Chemical -> thermal -> mechanical -> electrical -> chemical) and I think that's bloody dreadful! Now try to do better...actually quite hard.

In the end I got PV, but I'd still like a working alternator.

Dozer Dave

Your settling for a pv now but is there a better solution?

Direct drive portable cold fusion! :pac: :cool:

Actually BMW, Fiat and someone else I can't remember are developing thermopiles instead of alternators. Use the waste exhaust heat and spare the mechanical load. Expensive tech. though.

Dozer Dave

Is it possible that your Macgyver electrics are the main and sole problem of an altenator only lasting a year where as other people are getting years of service out of them. Is this your obsession for a voltmeter?

Yes but a simply larger concentric alternator would be up to the task.

My "obsession" for a voltmeter is a means by which to measure and monitor a system to an end to improve it.

Look at it this way if you were to insulate your house, first you would need a means to understand what the heat is doing.

On the other hand just burning more fuel to compensate for the loss would work too and it wouldn't require any research.

Dozer Dave

Sir Liamalot wrote: »

Yes but a simply larger concentric alternator would be up to the task.

Why have you not this fitted instead of the pv?

Less of a priority. I've a 120A in the post and overdue.

PV works harder, it produces less but more consistently with less waste heat, less engine wear, cleaner energy and works when I'm not there.
PV generally puts 3:1 electrons in my batteries compared to alternators.
On a good day I'd get 20A to the house batteries max from my current alternator.

When I say alternators are dumb...well they are, they're still effective though. I'm not knocking them just saying don't expect them to be sophisticated.

"New" alternator arrived today.

Someone dropped it on the B+ and smashed the rectifier into the casing.
..shorted diode somewhere...alas...round 3.

No such things as 9.5mm male blade crimps incidentally. Despite that 9.5mm females are freely available.
M5 ring terminals do the job.

bogman

Has anyone a link for a reliable durable voltmeter that can be mounted please

52mm gauge or panel mount?

Can't vouch for most of these but the datasheets look good. Probably need illumination for night-time driving.
Is this for the cab. or the living compartment?

0.3% accuracy sounds like a lot but on a 12v scale you need that accuracy otherwise the decimal is inaccurate which is ~12% charge or 25% usable.

http://www.ebay.co.uk/itm/12v-24v-3-WIRE-BLUE-VOLTMETER-BATTERY-INDICATOR-DASH-GAUGE-LED-CARAVAN-SOLAR-/251861780068?pt=LH_DefaultDomain_3&hash=item3aa421c664 3 wire is a good sign, one for power, one for measurement, having a sense wire bodes well, if it wasn't accurate then they wouldn't bother (easier read red LEDs than blue in daylight)

Anything you get on Ebay will need verifying with a trusted meter, some of them have a trimpot for calibration adjustment. Others sometimes you can just hack them with a well placed resistor.

Precision Panel Mount #1




Precision Panel Mount #2





Bargain Alert Battery Monitor




Personal Favourite ...pity it hasn't got an ammeter included.
The alarm functions are actually voltage sensing relays, you can autostart/stop a generator with it :cool:




This looks like a decent analogue 52mm gauge. At least the scale is wide enough to be interpretable and doesn't look entirely like it belongs in a rude boy car.




Make sure you wire it on dedicated conductors. No piggybacking +ives!! If you put the meter on a load carrying conductor you are not measuring the battery but the circuit it's attached to.

bogman

Excellent, lots to go on here, thanks for your input.

I'm blaming you for this Mr. Moodrater...all I needed was a hot-wired 20W resistor.



Pulley swapped from my tindernator.
Tested fine on the drill: 1.5A on near enough fully charged battery @ 14.4v.

Things to do tomorrow:

• Fetch a bigger conductor >35mm². The 16mm² I have earmarked won't do now.
• Swap alternators, fit shorter belt.
• Test alternator on old loom.
• Disconnect old B+ and label.
• Make battery cable.
• Run new B+ (9 times fatter) in flexible HT oil resistant conduit and connect.
• Swap 40A maxi-blade fuse for 150A mega fuse on B2B conductor.
• Remove 300A B2B conductor and terminate lugs with solder proper like.
• Wire manual B2B switch through coil of 200A M&B relay (don't have a 200A switch).
• Extend 150A cable from relay to deep cycles.
• Resist temptation to install another volt meter and ammeter.
  
  I've decided to leave the second switched circuit through the solar controller as is. The circuit is rated for > 45A with a 40A fast acting MCB. I'll reserve that switch for absorption/float which is the only time I'd need it.

moodrater

Sir Liamalot wrote: »

I'm blaming you for this Mr. Moodrater...all I needed was a hot-wired 20W resistor.



Pulley swapped from my tindernator.
Tested fine on the drill: 1.5A on near enough fully charged battery @ 14.4v.

Things to do tomorrow:

• Fetch a bigger conductor >35mm². The 16mm² I have earmarked won't do now.
• Swap alternators, fit shorter belt.
• Test alternator on old loom.
• Disconnect old B+ and label.
• Make battery cable.
• Run new B+ (9 times fatter) in flexible HT oil resistant conduit and connect.
• Swap 40A maxi-blade fuse for 150A mega fuse on B2B conductor.
• Remove 400A B2B conductor and terminate lugs with solder proper like.
• Wire manual B2B switch through coil of 200A M&B relay (don't have a 200A switch).
• Extend 150A cable from relay to deep cycles.
• Resist temptation to install another volt meter and ammeter.
  
  I've decided to leave the second switched circuit through the solar controller as is. The circuit is rated for > 45A with a 40A fast acting MCB. I'll reserve that switch for absorption/float which is the only time I'd need it.

Nice one, when you're planning on keeping the vehicle its an investment otherwise a massive waste of time

Just make sure theres nothing funky on your b+ before you fire it up this time.

You could double up the 16mm cable if you have it already.

Why the massive fuse on the B2B cable surely you won't want anywhere near that current or are Mr and Mrs 6V planning a family?

moodrater

moodrater wrote: »

Nice one, when you're planning on keeping the vehicle its an investment otherwise a massive waste of time

I'm just disconnecting and insulating the stock wiring, there's no need to pull it, I can always swaperoony later.

moodrater wrote: »

Just make sure theres nothing funky on your b+ before you fire it up this time.

Plan is patch the new alt. into the old loom, if it all looks ok then stoke her up with the side cutters in hand, if it works, refit the relic and off to the electrical wholesalers, then install the blighter...2.1kW Mwahaha!

I've got it down to 7 mins an alternator these days.

moodrater wrote: »

You could double up the 16mm cable if you have it already.

Don't you worry M, I'll find a good use for that 16mm² in time.
Nah, I hate that. Few reasons only I'd care about; it's untidy, the conduit or heatshrink needs to be a greater diameter than required, added contact resistance and the load balancing along the conductors becomes a product of the resistance of the terminations.
Now having said that I may go 16mm² to the busbar and 35mm² to starter, battery etc.
Really I should be Y-ing off the alternator between the battery banks as a more direct route but I'd rather not clutter the running gear and it's not like I'm loosing a whole lot on a 95mm² link.

moodrater wrote: »

Why the massive fuse on the B2B cable surely you won't want anywhere near that current or are Mr and Mrs 6V planning a family?

'cause that's the spec. Maxi blades only go to 100A iirc. Cables ought to be good for 150A. If yer gonna buy expensive fuses best not blow them eh!. Yeah realistically I don't expect to see more than 70A down that road, tbh I'm not changing that fuse for a long while because I'll only be using the upper limits of the new alternator come Wintertime.
...it might be a case of I say it here because it's good practice but I don't actually do it until it bothers me.:o


235Ah is enough, I have a hard enough time discharging 10% most of the year.
Next time I buy lead it'll be 2V. :cool:

Just finished fitting the hinges custom brackets for my relay...turns out it's 250A :pac: ...it's nearly 1.5kg...beast

Kevin McCloud

Sir Liamalot wrote: »

Now having said that I may go 16mm² to the busbar and 35mm² to starter, battery etc.

35mm² to the starter what size camper are we talking here?

2.3L but there's a 90Ah starter battery, 235Ah deep cycles, 250W refrigeration & 90W dry cell battery charging downstream of that.
Not that max. loading is as big an issue as keeping the voltage drop to a minimum.

35mm² to starter motor -> 50mm² to starter battery (stock) -> 95mm² to deep cycles -> 12mm² x2 circuits to DC loads