Van rewire project using Renogy DCC50S and Lithium

[bladerunner1968]

Hi All,

I am shortly going to be rewiring my camper to bring it up to spec for off grid solar etc as currently it only has a poxy 75ah lead battery. I've bought a 150ah lifepo4 along with the Renogy DCC50S for decent DC charging. Due to the leisure battery location I will be running 5 metres of 35mm pos/neg cables from the starter location to the leisure battery location near the driver's side rear wheel arch.

I'm getting confused about how to wire up both the DCC50S and fused 12v camper circuit to the leisure battery (LB): Do I just have a single feed (16mm2) from the DCC50S to the LB and another 16mm feed from the LB to the 12v fuse box or is it better to use a bus bar and have both the DCC50S pos output and the 12v fuse box pos input attached to the same pos bus bar and another 16mm pos cable from the bus bar to the battery (so only one pos cable attached to the battery as such)?

Thanks

 

[Deaky]

I'd just use the one cable to a common bus bar. I'd also use the van body for the -ve from the starter battery to the DC-DC charger, you don't need to run a separate cable

 

[Raul a/3]

A buss bar distribution is better, you can pick one like in the photo from 12v planet, or half price ebay. The ebay comes with very thin bar.

 

[bladerunner1968]

cheers guys just the job. I'll use the bus bar approach then. Is 100A OK?

 

[bladerunner1968]

I'd just use the one cable to a common bus bar. I'd also use the van body for the -ve from the starter battery to the DC-DC charger, you don't need to run a separate cable

I've already ordered the neg cable so may as well use it. I maybe wrongly read that for voltage drop the neg cable needed to be the same length/type?

 

[Deaky]

If you use a -ve cable then you’re effectively doubling your cable length.

 

[bladerunner1968]

If you use a -ve cable then you’re effectively doubling your cable length.

hmm so is that good? Are you saying that I don't need to run the neg back to the starter battery loc?

 

[t0mb0]

hmm so is that good? Are you saying that I don't need to run the neg back to the starter battery loc?

Providing you can get a good chassis ground connection, you don’t need a separate ground cable. Also, if you’re really using 5m of 35mm2 cable, you’ll be thankful of only needing one length, it’ll be incredibly heavy and unwieldy!

 

[bladerunner1968]

Providing you can get a good chassis ground connection, you don’t need a separate ground cable. Also, if you’re really using 5m of 35mm2 cable, you’ll be thankful of only needing one length, it’ll be incredibly heavy and unwieldy!

OK I understand now. So could I run a neg back from the leisure battery location (wheel arch area) to an earth point under the driver seat? Would that help?

 

[t0mb0]

OK I understand now. So could I run a neg back from the leisure battery location (wheel arch area) to an earth point under the driver seat? Would that help?

You just want the nearest solid chassis ground connection to your leisure battery. There most likely is one near the wheel arch somewhere.

 

[Deaky]

hmm so is that good? Are you saying that I don't need to run the neg back to the starter battery loc?

Exactly, moreover, you should not under any circumstances connect anything directly to the -ve terminal on the starter battery. Your leisure battery and your renology BC-DC changer should both be connected to the nearest OEM ground connection point to them.

 

[bladerunner1968]

You just want the nearest solid chassis ground connection to your leisure battery. There most likely is one near the wheel arch somewhere.

yes probably but it is likely hidden behind the unit which is solidly installed Hence wanting to route to a more accessible one such as under the driver's seat?

 

[bladerunner1968]

quick question - is it ok to use M6 terminal rings on a busbar with M5 posts?

 

[Raul a/3]

That’s what I used, with 5mm washers under the nut. I bought some brass bolts to change later, still in the box a year later.

 

[bladerunner1968]

That’s what I used, with 5mm washers under the nut. I bought some brass bolts to change later, still in the box a year later.

thanks - I have some 5mm copper washers so hopefully they will do the job

 

[bladerunner1968]

Unfortunately I'm having to rethink this. Due to space constraints where the LB is right next to the o/s rear wheel arch, I plan to fit the DCC50S charger under the driver's seat then run a 25mm2 cable from there to the LB. This is an approx run of 5 metres. Am I better with 16mm2 or 25mm2 cable from the driver's seat base to the LB located in the rear? The LB is a 150AH lithium

 

[t0mb0]

Unfortunately I'm having to rethink this. Due to space constraints where the LB is right next to the o/s rear wheel arch, I plan to fit the DCC50S charger under the driver's seat then run a 25mm2 cable from there to the LB. This is an approx run of 5 metres. Am I better with 16mm2 or 25mm2 cable from the driver's seat base to the LB located in the rear? The LB is a 150AH lithium

I think this is likely to be a bit of an issue, generally chargers specify they need to be fairly close to the battery to be charged. Given you've got a chunky lithium battery, we can assume it can/will utilise the full 50A from the Renogy, if we assume a charging voltage of about 14v over a one-way 5m run of cable (i.e. assuming a good earth to chassis), then you can use a voltage drop calculator such as the one below to give a voltage drop of 0.63 volts on a 16mm cable (and even 25mm gives nearly 0.4v). Unfortunately I would view this is a fairly significant drop which may affect the charging. It may be a different story if the charger measured the voltage at the battery (using a separate cable in parallel), and performed some voltage compensation but I'm not aware of any that do this. Alternatively, it may just be possible to set the charger parameters to charge at a higher voltage in compensation, but given the compensation requires varies as a function of current, this is likely not possible.

Voltage Drop Calculator | 12 Volt Planet

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

Whatever you do, make sure you have it all fused correctly if you're considering of sending 50A the full length of the van! Would be potentially disastrous if that shorted out somehow.

 

[bladerunner1968]

OK thanks - I'll have to try and squeeze the charger in somehow.

 

[Raul a/3]

I have done a quick calc for you.
At 14v 700w 50a, 5m distance with 35mm2 will have a drop of 0,3v
14v in 13,7v out,

And same 14v 700w 50a 0,5m distance with 16mm2 will have a drop of 0,1v ; 14v in 13,9v out.
Take your pick. Distance has a big impact on low voltage.

 

[Dellmassive]

Some good advice above.

The Great thing with the DC-DC chargers is that you can fit them farther from the engine than a standard VSR.

REDARC insist on having them fitted as near to the leisure battery as possible... Even when the battery is in the back of a towed caravan...miles away from the engine and alternator.

This is because the DC-DC can boost the output charge voltage to higher than what's coming in, even if this is much lower due to the voltage drop over a long cable run. (The only trade off is slightly less current available for charging.... That's just the physics of it.... )

So if say fit the charger at the back of the van.... Then get the best fattest cable you can buy..... As above, 50A is big boys toys. And needs appropriate respect.

If you don't fit a fat enough cable..... And start pulling 50A the cable will heat up and start melting stuff.... Like fuse holders etc. Or worse cause a fire.

So it's worth paying the extra now for decent gauge cable, fuses & fuse holders. (Use chassis ground for the NEG)