Caravan wiring question

[NAVVY]

Hi Guys,
When I purchased my van, there was no battery fitted, but obviously one had been fitted in the past. There is a 12vdc 4amp battery charger fitted which is powering all the 12v items in the van. My question is where in the circuit do I connect my deep cycle battery, so the charger will keep it topped up when 240v is available, or I have my genni connected. I have attached a diagram of the wiring as I see it, and would appreciate any suggestions. Apologies for the poor picture quality, hope it is legible.

 

[Old.Tony]

Exactly where you have indicated.

If the 4A charger isn't multistage with an auto 'float' mode then ditch it. Don't get the one from Aldi, it won't auto-start a charge, you have to press a button each time. You could get a C-Tek but realistically even a Powertech (Jaycar) unit will not kill your battery.

4A is a little underpowered as a supply. Your toilet pump will use 2A, Shure mains pressure pump will use 3 to 4A and then there's your lights. A single fluoro will use about 0.6A, one of those squarish Philips tubes will draw about 1.3A. Have a couple of lights on and turn on the tap and you're asking the supply to die.

 

[NAVVY]

Thanks Tony, I figured I might get a response from you. Thanks very much I appreciate your input. I was looking to upgrade the charger to the 40A unit on the sponsored link on this page. Looks like good value to me and I have had a good run with other purchases from this business. http://www.oo.com.au/3-Stage-240V-40A-Battery-Charg_P204752.cfm?cid=rm|net:criteo|seg:nodata|lnk:elbchc40a|cat:Electronics,%20TVs%20%20Computers&cm_mmc=Retargetingtech-_-Criteo-_-Nodata-_-%20Home&utm_source=Retargetingtech&utm_medium=Criteo&utm_campaign=Nodata

 

[Old.Tony]

That's a 3-stage charger - it will do the minimum required to look after the battery, but it has to be one awesome battery to be charged at 40A.

Most deep cycle batteries like to be charged at a fraction of their capacity. The toughest of these, the spiral-wound AGM batteries - are expensive, and given the $ involved you don't want to be deliberately destroying them. These can be charged at C/2 (but probably prefer C/3). That means that for my Optima D31A, I shouldn't charge it at more than 25-37.5A. I currently charge it at 7A peak.

For normal AGMs you'd charge at C/3.

For other liquid (flooded cell) batteries you'd charge at C/5.

For gel batteries, no more than C/10 - these batteries die really fast otherwise.

What kind of battery are you considering for that spot?

 

[NAVVY]

I currently have a century AGM battery as my aux. in the ute, and would possibly look at another one of these for the van if you think they are the most suitable for the job. If I was to go in this direction, what would you consider to be the best option for a charger? I have a local Jaycar branch here in Dubbo, is the powertech unit reliable? Which model?
Thanks Tony.

 

[Old.Tony]

AGMs are good. Great, actually. Far better than gels - here's why.

When the battery is charged, some hydrogen can be released - usually only when the charge rate is too high, or the input voltage is too high. This hydrogen is released at the boundary between the plate and the electrolyte. It's how batteries work.

In a flooded cell battery, that hydrogen bubble will rise to the top of the battery acid like any good bubble will do.

In an AGM battery, the bubble can't travel far, but it can still 'pop' because the electrolyte is still a complete liquid suspended in the glass mat.

In a gel battery, as the bubble forms the gel deforms and can lift away from the surface of the plate. This is why gel batteries shoudn't ever be charged at more than 14.1V or so (which means your alternator on a good or short cable is probably not the gel battery's best friend).

There's another option becoming available, and that's LiFePO4 (lithium iron phosphate). These batteries use different chargers because they don't respond like a lead acid battery, but they're half the weight with twice the power and 6 times the price (that may be a slight exaggeration but it's illustrating that they aren't cheap!).

If you're going AGM in the van so that the technology is all the same (allowing you to interchange parts as needed to manage temporary loss of function) then it's really a matter of HOW you want to charge it. The Powertech range isn't bad. I had one, it did a fantastic job. Doesn't look like Jaycar have the same range they had once before though, but if I had a decent capacity AGM (eg 120Ah) I'd feel confident charging it at 30A if possible making this charger the one to get if you can get stock, but this one is also a good unit (15A, makes for more flexibility with batteries later).