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DC DC Charger and MPPT controller combo - wiring question

pseudo

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Mar 19, 2020
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15
Hey all,

Looking at installing this 20A DC DC/MPPT combo in my van:


And I'm wondering if instead of wiring it as the manual suggests with a negative cable going all the way back to the engine battery:

dcdc manual.jpg

I could do the following instead to simplify the wiring and save on cable:

dcdc mod.jpg

With the ground from the house battery going to a metal part of the van body on the interior right next to the house battery (scraping the paint to make good contact).

Would this have the same result and work properly/be safe?

Thanks
 
Hey all,

Looking at installing this 20A DC DC/MPPT combo in my van:


And I'm wondering if instead of wiring it as the manual suggests with a negative cable going all the way back to the engine battery:

View attachment 254748

I could do the following instead to simplify the wiring and save on cable:

View attachment 254750

With the ground from the house battery going to a metal part of the van body on the interior right next to the house battery (scraping the paint to make good contact).

Would this have the same result and work properly/be safe?

Thanks
Using the chassis as your negative return is possible, but a terrible practice. Cheap, and full of problems. Every single connection will corrode and give issues over time. Setting yourself up for ground loops, faults, impossible to troubleshoot later. Even with just a single chassis to start battery negative connection, that one screw probably causes the most issues of all wiring reports I see here.

Ford started doing this early on when there was little electrical in a car, battery and starter, to save $$. All cars were huge beam frame construction, not unibody folded sheets. The practice has been the bane of automotive electrical ever since.

You should only have one single bond between negative and ground in a system. In a mobile system, the chassis acts as the ground. You are grounding every item.

Here is the official Diymobileforums paper on negatives and grounding, and describes the correct way to do it.


Just do it the correct way and run both a positive and negative wire.
 
Using the chassis as your negative return is possible, but a terrible practice. Cheap, and full of problems. Every single connection will corrode and give issues over time. Setting yourself up for ground loops, faults, impossible to troubleshoot later. Even with just a single chassis to start battery negative connection, that one screw probably causes the most issues of all wiring reports I see here.

Ford started doing this early on when there was little electrical in a car, battery and starter, to save $$. All cars were huge beam frame construction, not unibody folded sheets. The practice has been the bane of automotive electrical ever since.

You should only have one single bond between negative and ground in a system. In a mobile system, the chassis acts as the ground. You are grounding every item.

Here is the official Diymobileforums paper on negatives and grounding, and describes the correct way to do it.


Just do it the correct way and run both a positive and negative wire.


Ok thanks. So, since the start battery is already grounded to the chassis that's my single bond, and I can just connect the negatives from the solar panel, charger and inverter to the house battery and then run a negative cable from the house battery back to the start battery?

Like so?
dcdc better.jpg
 
Ok thanks. So, since the start battery is already grounded to the chassis that's my single bond, and I can just connect the negatives from the solar panel, charger and inverter to the house battery and then run a negative cable from the house battery back to the start battery?

Like so?
View attachment 254759
Actually the 1st picture in this thread looks clearer and correct. Follow the directions for your dcdc charger. There is a difference between isolated and non isolated... this one looks non isolated, which is ok for a van and truck. Yah the 2 pics are functionally equivalent but this last pic gives bad impression of wire lengths etc.
You generally run a long pos and neg from engine area and alternator/Start battery, back to cooler living area where the aux battery is. Then the dcdc +pv charger is back there with aux battery.
I would have a negative bussbar, and run one neg cable from aux battery to it--this is where you place a shunt if you want to measure total battery use, pv, etc. Then run a negative from pv to bussbar, from alternator to bussbar, and from bussbar to The NEG port of that dcdc charger. Basically make all the negative connections on bussbar, not aux battery terminal. You want that single neg aux battery cable connection to allow for a shunt and monitoring there.
Just the way folks draw their pics tends to influence where they run and connect cables is all. Less mistakes on what each wire is flowing for amperage and what size it needs to be, when drawn and built with a bussbar.
 
In some vans ( Transit / Sprinter ), they specifically call for using the factory ground points in the manual vs deciding which location is best on your own. At least for the return path to the starter battery.

The reason is that those vans contain the equivalent of a shunt for current monitoring to the starter battery, and by passing it off sets the monitor.
 
the chassis as your negative return is possible, but a terrible practice.
Many vans have smart alternators with sensors between starter battery negative and chassis/van metal. Thus any auxiliary power take off from the starter battery must use chassis/ van metal, not the battery negative terminal. Failure to follow this advice will cause vehicle charging issues . Usually there is a chassis earth point near the battery or seat base that can be used as a negative common point.
charger and inverter to the house battery and then run a negative cable from the house battery back to the start battery
You can, subject to the van not having a sensor in the starter battery negative path.

Your previous idea using a single point negative to the van metal would be OK. In this type of application, a dc to dc charger, the idea that using the van metal as a negative is a 'bad' concept, is false.
Provided only a single point is used and care is taken to make a good bond to the metal, the charger will function well.
 
@HarryN
@mikefitz

Interesting. However...
The fact some vans contain a shunt between chassis and start battery negative is not actually a compelling reason to run your negative return through the chassis... that is a seeming logic failure to me? All it means is you need to connect your negative returns to the chassis side of the shunt. Depending on how the shunt is wired, that may mean connecting to the shunt chassis bolt. I THINK that is what mikefitz was saying about an earth chassis point near battery already, so maybe just the same as I'm saying?

By definition the shunt has to live between the chassis and the battery negative to catch allll chassis return flow. Nothing about that recommends therefore using the chassis as a return--only that you don't skip over the shunt. All the benifits of NOT using chassis return still remain.

Am I missing something in these van chassis shunt return designs? To capture all chassis flow, shunt has to be a single return line to battery... how is this different than any car that uses a smart alternator with current sensing?

Thx. Good topic for discussion, this chassis vs negative wire vs grounds comes up allll the time here, along with isolated vs not. Your thoughts on this are interesting and I'm sure super helpful to folks reading here later.
 
Last edited:
@HarryN
@mikefitz

Interesting. However...
The fact some vans contain a shunt between chassis and start battery negative is not actually a compelling reason to run your negative return through the chassis... that is a seeming logic failure to me? All it means is you need to connect your negative returns to the chassis side of the shunt. Depending on how the shunt is wired, that may mean connecting to the shunt chassis bolt. I THINK that is what mikefitz was saying about an earth chassis point near battery already, so maybe just the same as I'm saying?

By definition the shunt has to live between the chassis and the battery negative to catch allll chassis return flow. Nothing about that recommends therefore using the chassis as a return--only that you don't skip over the shunt. All the benifits of NOT using chassis return still remain.

Am I missing something in these van chassis shunt return designs? To capture all chassis flow, shunt has to be a single return line to battery... how is this different than any car that uses a smart alternator with current sensing?

Thx. Good topic for discussion, this chassis vs negative wire vs grounds comes up allll the time here, along with isolated vs not. Your thoughts on this are interesting

I am not suggesting to use the vehicle chassis as the return path for the bulk of the auxiliary power system connections. Ideally, those should be close loop, hard wired only to itself.

So for a van that is just using solar power to charge the batteries ( my typical method ) the only attachment to the vehicle is safety ground related.

Specifically for BTB charging, that aspect should pass through the vehicle chassis.

So for instance on a modern Ford Transit, the ( + ) connection is CCP2 and the ground side is one or several of the factory specified ground locations.

The body of the vans are increasingly bonded together using industrial adhesives vs welded, so you can't count on the main body to be a significant current path, even if there is some electrical bonding when you measure resistance.

I was initially very skeptical of the method, but over time, have come to really appreciate using an inverter attached to the CCP2 ---- 120 vac charger---battery pack approach for BTB charging.

Most vans should have a 120 vac charger in them anyway, so all that is needed is a modest inverter.

But you can use your favorite method.

A promaster is not a transit, and the answers depend to some extent on the exact van, model year, and equipment set. The Ford CCP2 is an amazing feature, but they don't put it on all of them.
 
Hey all,

Looking at installing this 20A DC DC/MPPT combo in my van:


And I'm wondering if instead of wiring it as the manual suggests with a negative cable going all the way back to the engine battery:

View attachment 254748

I could do the following instead to simplify the wiring and save on cable:

View attachment 254750

With the ground from the house battery going to a metal part of the van body on the interior right next to the house battery (scraping the paint to make good contact).

Would this have the same result and work properly/be safe?

Thanks


Nope never i gone use this unit
Sorry but if i have to set my solarpanels minus connection to my battery.
Nope no thanks.

Than i go for a renogy model with a mppt (your model have a pwm )


Or this model.



Frans junk (yes i'm from the Netherlands)
 

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