| View previous topic :: View next topic |
| Author |
Message |
difflock
Site Admin
Joined: 03 Jul 2006
Odometer: 180
|
 Posted: Wed Jun 06, 2007 2:15 am Post subject: DiffMag: Dualmate Battery Management
|
 |
|
Summary of article: Adding a 2nd battery to most 4x4s to supply additional electrical equipment is an easy job. Charging the 2nd battery via a basic solenoid easy, but not always the safest or most efficient option.
View full article
Want to comment on this article? post your comments below.
|
|
| Back to top |
|
 |
|
|
:)
Mud Obsessed
Joined: 06 Feb 2006
Odometer: 4393
Location: Norfolk
1995 Land Rover Defender
|
| Posted: Wed Jun 06, 2007 7:13 am Post subject:
|
|
|
Some background ... I have built electric vehicles based on both lead-acid and lithium-ion batteries so I have some experience in this field. Part of my 'day job' is designing and building bespoke industrial equipment and based on my experience £235 is an awful lot of tokens for a production item such as this.
Err, excuse me but this is just scare-mongering...
| Quote: | | Conversely if the starter battery is fully charged but the leisure battery is flat connecting them together will allow the flat batterry to draw power from the starter. In most cases it won't draw much in the split second it takes you to turn the key but if, for some reason, you have turn the ignition on without starting (like waiting for your glow plugs to warm up) the flat battery could conceivably draw enough juice from the full starter to make it struggle when trying to start the engine. |
If you are warming your glow plugs the main battery voltage will be lower than the axillary battery so if anything the aux battery will be helping!
It is an urban myth that connecting two different capacity lead-acid batteries together will cause problems. Likewise, it isn't true that paralleling a fully charged battery to a partially charged one will cause significant charge to transfer, there may be a few milli-amps (that's thousandths of an amp) but nothing significant - and yes I have measured it.
| Quote: | | It will monitor the charge rates and warn you (with visible and audible warnings) when something is not right ... |
It is quite hard to measure charge rate, it needs to be done on electric vehicles and I have done it. The Dualmate doesn't measure charge rate, just voltage. Further according to the specification the voltage measurement is +/- 5%, that is potentially a huge error. If the display reads 14.00V the real voltage could be anywhere from 13.30 to 14.70V and the device is still in specification - on that basis what exactly is the point of those two decimal places?
Based on the above wouldn't recommend the Dualmate over a voltage sensitive relay, which will only connect the batteries when the alternator is charging, if you want to know the voltages a simple cheap LCD voltmeter can do the job with far more accuracy.
--
Tim.
__________________________________
-- Timothy Birt -- |
|
| Back to top |
|
|
Simon@Difflock
Founder
Joined: 10 Oct 2006
Odometer: 11328
Location: Orpington, Kent
1996 Land Rover Defender
|
| Posted: Wed Jun 06, 2007 8:46 am Post subject:
|
|
|
I will not argue that you have more experience than me in these matters but I have spent many, many hours researching the issue of auxillary batteries and the vast majority of the material I read backs up the scenarios I give (not from manufacturers websites either). I did use the phrase 'could conceivably happen' It will not happen in all cases but it could.
The voltage sensityive relay with LCD read-out you mention will, of course, do the job, but so will a cheap £20 relay off ebay. But it is only efficient when everything is going well, the alternator is performing properly and the batteries are in good condition.
I still recommend this unit for a simple, reliable, peace-of-mind solution. When we're travelling I can easily monitor the batteries and the charging characteristics and if something is not right it will intervene and warn me before it becomes a real problem. A voltage sensitive relay will not do that. My only warning will be that the batteries are no longer providing the level of power that they once did. At which point it may be too late.
I am a great believer in simplicity and have been happy with dumb relays in the past, but I've never been more than a few hours from home and never had to rely on them. If I get to a position where I'm a few weeks from home I'd like a heads-up warning before it gets to the 'oh crap!' stage.
|
|
| Back to top |
|
|
:)
Mud Obsessed
Joined: 06 Feb 2006
Odometer: 4393
Location: Norfolk
1995 Land Rover Defender
|
| Posted: Wed Jun 06, 2007 9:09 am Post subject:
|
|
|
Simon,
You did say "post your comments below", so I did. 
--
Tim.
__________________________________
-- Timothy Birt -- |
|
| Back to top |
|
|
Simon@Difflock
Founder
Joined: 10 Oct 2006
Odometer: 11328
Location: Orpington, Kent
1996 Land Rover Defender
|
| Posted: Wed Jun 06, 2007 10:45 am Post subject:
|
|
|
I know, and I welcome the debate. 
|
|
| Back to top |
|
|
Simon@Difflock
Founder
Joined: 10 Oct 2006
Odometer: 11328
Location: Orpington, Kent
1996 Land Rover Defender
|
| Posted: Mon Jun 25, 2007 9:31 am Post subject:
|
|
|
Hello Tim
I've been in touch with Ace Communications who manufacture the Dualmate and they confirm that the error rate of 5% mentioned in their literature is wrong, since I bought mine the documentation has been corrected to 1%.
They also mentioned that my comment about measuring the charge rate was not entirely correct (as you stated) The Dualmate measures voltages only so it will measure the voltage of the batteries at rest (engine not running) and while being charged. The reading while the engine is running should be around 14.2 - 14.5 volts depending on your vehicle/alternator.
Thanks for your input.
Simon
|
|
| Back to top |
|
|
Guy Hill
Gate Opener
Joined: 03 Jul 2007
Odometer: 2
|
| Posted: Tue Jul 03, 2007 10:44 pm Post subject:
|
|
|
Can I suggest that if you are serious about getting the best out of your batteries that you have a very good read of Sterling Power Product's website http://www.sterling-power.com/index.php .
No connection etc. just a very happy user of one of their mains chargers and now an alternator-battery charger.
Following a lot of research, I bought 3 cheap n cheerful (£42 ea.) 110Ahr 'leisure' batteries 1 engine 2 'domestic'. I run a large (3Kw) inverter and the difference a proper charging system made to the available capacity was astounding. With the a standard voltage sensitive relay system, using the alternator alone, the domestic bank never reached full charge. (hence the purchase of the mains charger) After the installation of the A-B charger I never have to top them up overnight.
Yes the gear is expensive (for 4x4 use), but you use the cheapy batteries which should last a few of years of my abuse (regular deep cycling to about 60% & discharge rate of 100-300A).
Only my 2p worth
|
|
| Back to top |
|
|
|
