Thread: Do I need a BCDC charger?

Originally Posted by Vern

Matson Bluetooth Wireless Battery Monitor - Supercheap Auto

These seem like a pretty good way to monitor your batteries

That’s kinda cool & comparatively priced to a dash mount 52mm gauge. Thanks.

Originally Posted by Vern

Ebay ones of the one i linked? Are they bluetooth as well?
All the ones i have seen on eBay (of what i linked) go from $40 and up.

2 in 1 Digital Voltmeter Thermometer 12V/24V Car Cigarette Lighter Dual Display | eBay

Doesn't a Bluetooth unit require the use of a phone to read the voltage?
NOT a great idea to muck about with your phone when driving even if you do want to check your battery voltage

Originally Posted by trout1105

Doesn't a Bluetooth unit require the use of a phone to read the voltage?
NOT a great idea to muck about with your phone when driving even if you do want to check your battery voltage

I would never do that - that’s illegal u know!

I should clarify that the OP pics were taken stationary in a car park!

I’ll voltmeter check all 3 batteries tomorrow or Monday.

Originally Posted by John_D2

2 in 1 Digital Voltmeter Thermometer 12V/24V Car Cigarette Lighter Dual Display | eBay

Another one But cheaper for the exact same unit
2IN1 Car Voltmeter Digital Voltmeter Battery Monitor Thermometer Blue Display | eBay

Originally Posted by John_D2

I do have the Bluetooth dongle that attaches to my Victron 100/30 mppt.

What you have is giving you just what the solar is doing to the battery. The BMV gives you everything that is happening to the battery. Part of this would be solar which you could get from your Victron app on your phone, part could be from the tug charging. The BMV also shows what has been drawn since the last full charge & this is offset by the charge going into the battery so give the state of charge of the battery.

Originally Posted by V8Ian

I've always been led to believe that a slow or trickle charge is better, a fast charge is only a "surface" charge and will discharge quicker.

No, not at all. Nothing wrong with a bulk charge - the battery will draw what it needs at that particular moment. If it is down a long way, it will pull quite a bit of current (if you let it) and charge quicker. Amp hours in equal amp hours out, minus a few inefficiencies.

Say your battery draws on average over an hour 20 amps - in reality, it would start out at 40 or so if quite flat, then the current would drop off as the battery accepts a charge - in that hour you've put in 20 amp hours, which you can now use when you pull up for a cuppa. Lets say your DCDC device is rated at 10amps and limits the current flow to your battery to just that for the same hour - now you have 10 amps hours in your battery to use - half as much for the same time. That's just an example but pretty close to the truth in reality.

My 2 x 100Ah batteries can draw 60 odd amps when I first start the car if they are low and it's been cloudy. An hour later, they are drawing around 20 amps, and a hour after that around 12 amps which they draw for quite a few hours before droppng down lower as they fulky charge - this is on a long run as well, so if your DCDC device is limiting the current- in my case, I'd pull up in the evening with only half charged batteries.

I've run this system for 5 years and never had battery issues - towing it with a variety of vehicles. I do have 150 watts of solar on the van too which certainly helps when the suns out, but remember I live in Victoria.... 😉

When your battery is quite full, it may only draw a few amps - this is irrespective of if you do or don't have a DCDC device - you can't force more current into the battery than in needs at a given time (unless you bring the voltage up even higher which can damage the battery)

Surface charge is what you see when you've been driving or charging your batteries for a long time and a voltage slightly higher than what is actually going on is seen if measured. A couple of minutes with a load on the battery will wipe the surface charge off.

Originally Posted by Nmritchie

I edited my earlier post to be clearer. Isolating the secondary batteries from the crank battery when the engine is not running is essential whatever system is used. The DC DC chargers make that simple by using an ignition wire to ensure that no current is drawn from the crank battery unless the alternator is running.

DC DC units are about optimising the charging of all batteries, and that is even more important when different types of battery are used - crank, auxiliary and trailer.

neil

Without meaning to put you down here, this seems to be one of the biggest myths that seems to be out there - a lot of websites and forums, etc continue this so it is completely understandable that it is accepted as gospil. Each battery will draw what it needs at any particular moment depending on its state of charge. You can have an almost fully discharged deep cycle battery connected to an almost fully charged cranking battery running off your alternator without issue. Different AH ratings, sizes, everything - doesn't matter.

I can't think of an arrangement (except lithium) that couldn't run like this.