DC-DC charger setup question

[mad85]

Currently working on installing a second battery and DC-DC charger in my Discovery 2. My requirements are that I do not lose offroad capability, and that I have a 1000W inverter mounted in the boot. I also do not want to loose any boot space, so the new battery will go instead of the compressor, mounted on the chassis, as mine is now converted to rear springs.

Does anyone think of anything why the following diagram would not work (i left required fuses out of the diagram for simplicity). Mostly interested in your opinion re wire thickness and if it would be ok to connect live wires from the dc dc charger and load to the battery through a distribution block rather than at the battery terminal. Anther question is, do I need to run earth wires or can I use the body/chassis for earth? maybe I can add a few more earth straps to improve the earth throughout.

I plan on purchasing a CTEK D250S (i know its an old model but I did find it at a very good price).

 

[rayra]

Yeah, skip the DC-DC charger fad and just install a $50 combiner solenoid solution so that both your batteries are charged when your vehicle / alternator is running. Hook your solar (if any) to your 'house' battery and thus keep your Primary / starter battery isolated from any draws while camping.

 

[dreadlocks]

Check your wiring gauges here: http://circuitwizard.bluesea.com/

A distribution bar for DC charger is fine, most have house batteries on a master disconnect switch and they would be wired up much the same way.. oversize the hell out of the wiring between the battery and its bus bar and its going to be effectively the same point.

An Inverter of such size should be hooked directly to house battery ground, RTFM on it.. they should give you wiring sizes/distances maximums and minimums, but smaller loads off chassis ground is acceptable, redundant engine and battery grounding straps would be a good idea.. will make it a bit more resilient if your not running ground back to battery.

 

[shade]

What are you using for a leisure battery?

 

[SquirrelZ]

One important consideration is the type of batteries, their capacity and their age. If the batteries chemistry (typical lead acid, AGM, Lithium, etc) is identical with age and capacity similar, a combiner solenoid would be worth considering. With dissimilar chemistry in the batteries, the optimium charging profiles are probably different. If you go with the one-size-fits-all combiner solution its very likely reduce the life of one of the batteries. You'll have reduced life also if the batteries are significantly different in age or capacity.

The DC to DC charger avoids those problems, which might be why you've chosen that solution.

 

[rustypayne]

I've been using the CTEK D250sa for the 2nd battery in my JKUR for a little over 2 years and it's been flawless. I keep a Dometic CFX50 running pretty much 24/7. 100ah AGM and 100 watt Renogy solar panel connected direct to the CTEK. I hooked it up according to the schematic in the CTEK manual. 10awg ~3 meters to the starting battery w/30amp fuse, I ran both the 12v & gnd from the front.

 

[luthj]

What purpose does the 100A switch serve? Is it just for isolation/disconnect or?

You must have a fuse on the DC-DC feed, as close as reasonable to the tie-in point. Obviously your second battery needs a fuse for its output as well. This needs to be as close to the battery as practical. If you can't put a fuse nearby, a few feet of unfused cable is okay as long you protect it very well.

If you are using a flooded lead acid battery, make sure you have access to top off the water.

Make sure the DC-DC can be configured to match the battery makers specs. Do not trust the generic profiles, make sure to verify the voltages.

As Dreadlocks indicates, check your voltage drops, make sure to include round trip wire length if applicable. You want less than 3% drop on the output of the DC charger in order to optimize charge rates.

 

[mad85]

thanks for all the replies. As some have guessed I am using a flooded as a starter and agm as the leisure battery. The 100A switch is more of a main switch if I want to turn off everything.

For fuses are was going to have a 30A midi fuses, one between dc dc charger and live battery (as close as battery as possible). Another 30A fuse between the dc -dc charger and the distribution block. Im not sure if I should put another near the leisure battery, although with my setup, it will have to be a 100A midi fuse. Would that work and be safe?

 

[dreadlocks]

All batteries should have a master fuse on em, should be sized adequately it would never normally trip.. its only job is to keep that pile of lead from unleashing hundreds of amps upon your poor electrical system, which often results in fires and batteries exploding.. its big day on saving your rump will be in events such as rollovers, etc.

 

[Herbie]

Agreed. The scenario I always picture is break-over on a rock that pinches a long-lead to the chassis. Theoretically could start a fire with TWO different batteries in one go!

 

[rayra]

Agreed. The scenario I always picture is break-over on a rock that pinches a long-lead to the chassis. Theoretically could start a fire with TWO different batteries in one go!

That's why the the leads should be attached to run along the top of the frame


IMAO a DC-DC charger is a terrible setup on a vehicle system when a much higher rate of charge is built right into the vehicle already. People are paying a premium for a DC-DC charger to reduce the rate of charge available to their 'house' system. In both the wiring diagram in this topic and in this one -

Dual battery in-cabin and Solar setup

Dual battery Plans in the works, few questions and sorry for the long-winded post. I plan to build a battery box enclosure that will rest behind the future Goose Gear drawers. I've still got a few questions prior to attacking the building part, such as: 2-AWG or 4-AWG run from primary battery...

www.expeditionportal.com

the DC-DC charger is necessarily hooked to the starter battery and is apparently the only power source to the 'house' side of things. 20-25A supply. Negating the much higher charge rates available from the vehicle's built-in DC charger. It seems a very poor idea to be paying a premium for these devices to reduce the available rate of recharge.
And frankly a poor idea altogether to be drawing from the Starter battery for any 'house' use. I mean the entire / base premise of the Starter / House concept it to isolate the starter battery from ancillary draw / wear and tear. I mean you might as well do away with the fiction of a 'house' setup, if it is predicated on siphoning power from the Starter battery. Just go right to a dual-parallel battery setup and be done.

 

[dreadlocks]

story time, few decades ago I bought an abomination of a race car from a kid once who mucked it all up, was stupid cheap because how bad he messed it up.. I'm limping it home from across the country, takes constant repair to keep it on the road.. when in the middle of BFE Illinois the car just up and dies, everything cuts off.. vehicle dead..

PO 'relocated' the battery to the trunk, I toss all my camping gear and tools in the truck into the ditch to test the battery.. with no multimeter I try to short the posts w/a screwdriver and much to my surprise, nothing.. so I disconnect the battery and go to pull it out, and its like >200F and swelled up.. have to wrap my dirty clothes around my hands/arms so I can get a grip on it and throw it out of my trunk onto the side of the road... a dude on a goldwing gave me a ride to a nearby tractor supply store and then gave me a ride back holding a giant tractor battery in my lap.

Hook the new battery up and it arc's something fierce, so I disconnect it and start chasing his wiring.. under the car, I found the battery cable welded to the exhaust.. I ripped it off, insulated it with some flattened soda cans wrapped around an old sock , managed to get the thing running long enough I limped it to nearest Autozone.. where I promptly wrapped that section of wiring up with some radiator hose and aluminum foil.

When I got home it took months to get that car sorted out, but when I finally did damn it ran great and I had about +$10k in free performance parts on it.. ended up being the fastest car I've ever had, and the least expensive too..

the TLDR of the story was, the vehicle's PO nearly sent me to a firey grave because how crappy his unfused battery relocation went.

 

[Martinjmpr]

IMAO a DC-DC charger is a terrible setup on a vehicle system when a much higher rate of charge is built right into the vehicle already. People are paying a premium for a DC-DC charger to reduce the rate of charge available to their 'house' system. In both the wiring diagram in this topic and in this one -

Dual battery in-cabin and Solar setup

Dual battery Plans in the works, few questions and sorry for the long-winded post. I plan to build a battery box enclosure that will rest behind the future Goose Gear drawers. I've still got a few questions prior to attacking the building part, such as: 2-AWG or 4-AWG run from primary battery...

www.expeditionportal.com

the DC-DC charger is necessarily hooked to the starter battery and is apparently the only power source to the 'house' side of things. 20-25A supply. Negating the much higher charge rates available from the vehicle's built-in DC charger. It seems a very poor idea to be paying a premium for these devices to reduce the available rate of recharge.
And frankly a poor idea altogether to be drawing from the Starter battery for any 'house' use. I mean the entire / base premise of the Starter / House concept it to isolate the starter battery from ancillary draw / wear and tear. I mean you might as well do away with the fiction of a 'house' setup, if it is predicated on siphoning power from the Starter battery. Just go right to a dual-parallel battery setup and be done.

I don't agree. On my Suburban where I had a relatively simple electrical system and a space for a 2nd battery, the dual battery option worked (although I would point out that because of the size restrictions in the battery area, I was required to use a specific battery size that limited me to a 68ah battery that cost almost $300!)

Modern vehicles with less room under the hood would require the house battery to be placed at some distance from the main battery and require running heavy, expensive 1 or 0AWG cable which is both cumbersome and expensive.

The prospect of introducing a variable of a second battery into the complex electronics of modern trucks is also something to consider. Many vehicles nowadays have what amount to battery monitoring systems that are designed to read the relative health of a single battery, and introducing a second battery into that (which the manufacturer never intended it to be able to deal with) is not something to be undertaken lightly and potentially could bring in a slew of other problems.

By contrast a DC-DC charger allows you to put the house battery wherever you want and you only need to run cable heavy enough to handle the current that the charger will be carrying - from what I've seen they are all under 50A which means you can run 4, 6, 8 or even 10 AWG cable, much less expensive and much easier to deal with. It also gives you much greater flexibility in what kind of 2nd battery you can run because it doesn't have to "match" the starter battery since they're not, technically, connected together. So you can have a flooded starter battery and an AGM house battery, or even a Li-Fe because you can adjust the charger to match the charging profile of the battery to be charged, something you can't do if you're charging both batteries from the alternator.

And finally I can't speak for anything but the Renogy DC-DC charger I have, but it won't draw down the starter battery because it has a relay - you know, exactly like an isolated dual battery setup does - that prevents the DC-DC charger from drawing power off the starter battery unless the ignition is on.

 

[Rando]

I would also disagree about DC-DC chargers being 'terrible'. In some situations they are not necessary, but in may they are. In most modern vehicles the alternator is controlled by an ECU and the operation is dialed in to charge the starting battery and provide for the stock loads while minimizing parasitic loads on the engine. They are not designed to charge an extra house battery and they will quickly drop back to a lower voltage, providing very little charge to the house battery. Modern Toyota alternators are definitely this way - they rapidly decrease output to 13.6-13.7V. If you want to get a decent amount of power form these to a house battery you either need to over-ride the ECU or get a DC-DC charger.

Almost all DC-DC converters only come on when the car is running, so they do not draw down your starting battery.

 

[mad85]

thanks again for answers.

the dc-dc charger is the best way forward for me because it has the following features which are important:
1. Can ensure the leisure battery is properly charged even if it is different type/age than the starter battery. IN my case I have a flooded battery for cranking and agm as leisure.
2. Ideal for locating the leisure battery away from starter battery. In my case it will be fitted near the rear chassis so it is relatively close to the inverter.
3. Can work as an MPPT solar charger, so I will not need a separate solar controller if I fit a 100W panel on the roof rack.

Following the feedback i have decided to run extra earth cables unless there is absolutely no way of passing them. Hopefully tomorrow I will start working on this and will be able to share a few photos.