Leisure battery cheap cabling?

[grantw]

I've been taking a look at many options for my leisure battery install and recently came across this:

http://www.amperorassociates.co.uk/r-power-resources/z-reference-Power_PI_battery_charger_MPPT.html

For the price (£170) it sounds quite good DC to DC charger it has the following features:
- 4 stage charging
- 25 amp charging at 14.5volts
- 2 x 100w solar/wind inputs

To find out more I emailed their customer support who came back with:
Our Power Integrator is designed to charge the vehicle battery from a solar panel input when the engine is stopped, it will charge the starter battery at 1A and stop when it reaches 12.5V anything that is generated above that or when the starter battery is above 12.5Volts will go into the leisure batteries. When the vehicle is running the alternator is fooled into thinking the starter battery is low and the voltage and current is diverted into the PI and through the four stage charger, as the batteries charge level comes up the amps going into the battery reduce till they are full.

Q:You mention that the PI will shutdown when the start battery "vehicle battery being lower than 10.5V" is:
A:This voltage is set to turn the PI off if the battery has developed a fault only.

Q: this voltage too low?
A: This voltage level is stops the PI try to charge a faulty battery.

Q: what is the maximum battery bank size the unit can charge?
A: We would recommend the maximum 240Ah we recommend the batteries are a matched the same make, model and size.




A question I have for you guys ... is their claim possible about tricking the alternator and effectively be able to 4 stage charge the main start batteries? I can't see how this works seems how it all just sits inline.

 

[Jon Wildsmith]

tricking the alternator just means it draws a high current and then the DC-DC part of the device converts it to a voltage and current appropriate for the current charging phase. All very standard DC-DC charger stuff with extra inputs for solar and or wind. Not sure about their claim of that being unique, I thought one of the other popular chargers who's name escapes me at the moment does the same.

 

[yogi]

This might be a silly question, but whats the difference between a DC-DC charger and a split charge system? Sorry if this is dumb!

 

[Jon Wildsmith]

A split charge system just connects the starter battery and aux battery in parallel and they are then both charged by the alternator which is a fairly dumb device. To charge the battery properly needs the voltage and current to be managed more intelligently. There's a pretty graph on the link Grant gave in the first post if you scroll down the page a bit. That shows the different stages of charging that are needed to charge the battery properly. A DC-DC charger take the power from the alternator and applies it more intelligently i.e. it manages the voltage and current so the aux battery is charged properly.

 

[yogi]

Ah that makes a lot more sense now, so essentially to keep a leisure battery properly charged over a long period of time, a DC-DC charger would be pretty much essential then? How come the alternator manages to charge the normal 12v battery under the bonnet properly then? Is this to do with leisure batteries being deep cycle battery type? Thanks

 

[Jon Wildsmith]

the alternator is ok for topping up a battery but if you discharge it a bit too much it will never be properly recharged by the alternator. Typical use of a starter battery means you won't really notice this but on an aux battery that you will tend to discharge quite a lot you get reduced capacity relying on the alternator alone. Depending on your requirements that reduced capacity may be enough though,

 

[grantw]

Thanks for more info Jon.

With DC-DC chargers pulling more current from the alternator would this also increase the alternators voltage and thus having an undesirable affect on the start batteries?

 

[Jon Wildsmith]

With DC-DC chargers pulling more current from the alternator would this also increase the alternators voltage and thus having an undesirable affect on the start batteries?

This will be fine and is no different to having any other load connected.

 

[Graham]

When I was looking to supply 12v to the 2kW inverter, I was originally looking at 50mm welding cable.
But then decided that 35mm was more than man enough.
It's not like I am going to run the inverter on full 2000 watt loadings,, it was put in so it wouldn't be working flat out, a bit of reserve capacity.

If you have an inverter, perhaps an "intellegent charger" simply plugged into the inverter would work as good as anything?

Gra.

 

[yogi]

When I was looking to supply 12v to the 2kW inverter, I was originally looking at 50mm welding cable.
But then decided that 35mm was more than man enough.
It's not like I am going toi run the inverter on 2000 wat loadings,, it was put in so it wouldn't be working flat out, a bit of reserve capacity.

If you have an inverter, perhaps an "intellegent charger" simply plugged into the inverter would work as good as anything?

Gra.

I wondered that as well and I can't see why it wouldn't with a pure sine wave inverter anyway?

 

[Jon Wildsmith]

just not as efficient going from nominal 12v to 240v and then back again plus you'll have to arrange to switch it all on and off when the engine is running / not running which the DC-DC chargers sort out for you ... so you could do it, it just isn't a great way to do it.

 

[grantw]

Thanks yet again Jon.

With the inverter route I also want to avoid having 240v inside the truck.

I **think** I finally understand enough about how all this works to actually start buying some equipment.

One other very similar charger to this is the CTEK-250s but it comes in at around £80 more and 5ah less on the charge side. This might be the one you meant? http://www.themotorreport.com.au/51965/ctek-d250s-dual-dc-dc-12v-20-amp-5-step-charger

As these chargers only require around 30ah I guess you can also use cable something like this http://www.ebay.co.uk/itm/20-Metres...ls_Supplies_Electrical_ET&hash=item27d1d2564b

You don't have to worry about voltage drop as the charger steps this up and if I googled correctly 10mm cable should carry 70amps?

If anyone knows of a better value DC-DC charger I'd love to know about it

 

[Jon Wildsmith]

One other very similar charger to this is the CTEK-250s but it comes in at around £80 more and 5ah less on the charge side. This might be the one you meant? http://www.themotorreport.com.au/51965/ctek-d250s-dual-dc-dc-12v-20-amp-5-step-charger

That's the one, a few on here have used that and its sibling, seems a nice if expensive setup. Don't forget that any accessories running directly off the aux battery during charging will a) take power away from the battery and b) may/will fool the charger as to the batteries status. The CTEK combo caters for that and will do a better job than a DC-DC charger on its own. I use a pair of solenoids, one of them a change over solenoid, both controlled by my Arduino gadget, that switch the accessory feed to run off the alternator circuit during charging so the DC-DC charger has a clear run at charging the aux battery in isolation.