[Guide] DC-DC Charger (for leisure battery) -- How I Done It --

[bladerunner1968]

@Dellmassive when using your DCC50S, did you happen to have any issues pushing out more than 30AH sustained into the leisure lifepo4?

Something 'kill's the charge into my new 150ah lifepo4 after 20 seconds or so when the DCC50S is on the 50A setting, 1 minute or so when on the 40A setting but is fine on the 30A setting. After a minute the charge picks up again and repeats. I had a clamp meter on the starter battery -> DCC50S positive cable near the DCC50S end which shows just over 55A until the charge dies so it is definitely not voltage drop. The BMS reports 48AH incoming to the battery too.

Any ideas on where to look? The lifepo4 BMS input amp is set to 100A so that shouldn't be a problem .The DCC50s boost charge setting is set to 14.0v which is what the battery initially requires

 

[Dellmassive]

No issues with mine on 50A.

I need the have the battery below 80% soc for it to pull the full 50A. Above that it deminishes.

I use the APP to set the max charge to adjust to the battery I'm using.

Your setting of 14.0v seems low?..... Most lithiums like 14.2-14.6V for a charge.

Your symptoms seem to indicate a heat issue when pulling large current.

Is the charger getting hot?.... Have you got a loose connection?

Is your battery BMS overheating? (What's it rated for)

What cable and fuses are you using,?

What battery and setup?.... Post s few pics of yours.

Well see if we can help.


....

Currently running at 20a or 30a ATM to keep everything cool while I'm testing some inverters.



.

 

[bladerunner1968]

again, 30 AH input is no problem - only when I set the charger to 40AH or 50AH output do I have issues

 

[bladerunner1968]

Here is the battery input that the BMS reports just before something kills the charge

 

[bladerunner1968]

@Dellmassive We don't need to look further into my lifepo4 battery charge issue - after speaking with the battery supplier this morning I did some further voltage tests and sure enough - the root cause is: voltage drop across the 25mm2 cable. When the charger is pushing out 40A or more I saw that the voltage reading at the charger drops from 14.34v down to 13.2v when the charger is at max which is too low for the charger and that is what causes the charger to stop. On the lower 30A setting, the lowest the input to charger voltage drops to is 13.85v which is OK for the charger. It will have to stay on the 30A output setting

You are getting 50A because you are so much closer to your starter battery.

 

[Dellmassive]

@Dellmassive We don't need to look further into my lifepo4 battery charge issue - after speaking with the battery supplier this morning I did some further voltage tests and sure enough - the root cause is: voltage drop across the 25mm2 cable. When the charger is pushing out 40A or more I saw that the voltage reading at the charger drops from 14.34v down to 13.2v when the charger is at max which is too low for the charger and that is what causes the charger to stop. On the lower 30A setting, the lowest the input to charger voltage drops to is 13.85v which is OK for the charger. It will have to stay on the 30A output setting

You are getting 50A because you are so much closer to your starter battery.

is your setup in a T6?

mine is . . im using the OEM split charge relay feed cable.

its fed from the SA fuse box with a 100A fuse ( i think)

then fed to the passenger seat base and down rated original MAXI 80A fuse (swapped out for a 80A MIDI fuse)

via the 100A relay to the leisure battery.

++++++++++

The Renogy DC50S is in this location. . . . so about 4/5meters to starter battery main fuse box.

im running 8AWG silicone cables and 50A Andersons for testing . . . .

which get HOT above 40A . . .

so i limit my 50A chargeing for testing . . . and run 20-30-40A for normal day to day.

 

[bladerunner1968]

Mine is a T5 with aircon (better alternator?) and I have the dcc50s and LB next to the rear wheel arch (LWB) just over 6.5 metres away from the SB. Seems this is too much for the voltage drop despite me only having a 1.5 metre run for the negative cable to chassis earth point underneath the LB

I have the same inverter as you too. Also mine is the latest dcc50s - not sure what the changes are TBH..

What is your voltage reading at the dcc50s input terminal when you are pushing out 40AH to the LB?

 

[Dellmassive]

Mine is a T5 with aircon (better alternator?) and I have the dcc50s and LB next to the rear wheel arch (LWB) just over 6.5 metres away from the SB. Seems this is too much for the voltage drop despite me only having a 1.5 metre run for the negative cable to chassis earth point underneath the LB

I have the same inverter as you too. Also mine is the latest dcc50s - not sure what the changes are TBH..

What is your voltage reading at the dcc50s input terminal when you are pushing out 40AH to the LB?

ok . . . for 6.5m ( all the way to the back of the van)

you may need to replace the cable for a larger one.

or.

double up and add a second cable.

.............


ill do some testing tomoz and get some numbers for you.


+++++++


edit:

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

25mm2 is showing 0.5v drop over 6.5meters (about 4%) so on the limit for that distance.

 

[bladerunner1968]

@Dellmassive did you manage to do any testing? Would it help if I beefed up the negative cable from 25mm to 35mm for the 1.5 metre run?

 

[Dellmassive]

Not yet.... Busy weekend. And been a bit windy.

But I have run the battery down to 20% ready for a full rate charge test.

All cables should be fat as possible.... Why is the NEG so long? (1.5m) .... Just conect it direct to chassis ground. 30cm.? Again try doubleing up.

Try using a jumper cable to double up for testing....you might have a bad join or crimp somewhere.

Try double up the starter feed cable with a temp cable for testing.

Post some pics so we can see what's what.... Of the cables. The fuses. The battery s. The charger etc etc.

 

[Dellmassive]

@Dellmassive did you manage to do any testing? Would it help if I beefed up the negative cable from 25mm to 35mm for the 1.5 metre run?

@bladerunner1968

done some testing the other day.

i run the battery down to 11% SoC . . . so it was ready to take full rate charge.




to validate the readings i have the Victron smart bmv712 which shows the battery at 15% soc.





.

setting the Renogy DC50S at lithium profile and 50A max charge rate, we start the test.

Engine running on the drive with no other loads going on - i have the 180A alternator and the OEM 50A/80A/100A feed to the seat base.





.




.

the passenger seat base . . . .





100ah Renogy lithium is under drivers seat . . .





.



keeping an eye on temps with the thermal . . ( due to me having 50A andersons for quick swaps of kit)





we can see a hot spot on the MIDI fuse bock that looped over to the battery . . .

obviously a poor connection or a iffy fuse causing high resistance and heat build up.



here is the result after 30mins . . .

50A flat rate for full time , BULK charge from charger.

battery voltage rises from 13.2v to 13.6v . .



SoC rises to 37% . . .




confirmed on the Renogy APP...






.


here is the BM-2 plot for the day, showing the battery voltage rise . . .






.

 

[bladerunner1968]

@Dellmassive really great thanks for testing/posting.

Did you look at the voltage reading at the Renogy end of the starter battery -> renogy +ve cable using a multimeter whilst the 50A charge was going in to see how low it drops? Mine drops below 13.2 after 20 seconds when on 40 or 50A charger setting.

Also how long is your starter battery -> Renogy +ve cable?

 

[Dellmassive]

Renogy DC50S showing starter feed at 14.1v under 50A load . . . (alternator prob at 14.6v while engine idle)

cable run is factory from starter battery to under drivers seat . . . about 3-5meters.

but not tested with meter as its all working well . . . .

 

[Lukefx]

Hi all, after some advice please. I've just started my leisure battery install and found all of these live wires under the double bench. Can anyone tell me if these are the pre-wired cables from the factory for an auxiliary battery? I'm not sure if you can see from the pics but one is around a 5mm cable which looks like it goes straight forward under the carpet. If it is can I just tap into it here and fuse it for the split charger or would it need to be fused at the starter battery?

 

[Fishd]

Doesn't look 'factory-fit' to me... any previous owners for your van? Perhaps having an amp / subwoofer installed under the seat?

You need a fuse as close to the starter battery as you can... the idea being that the fuse goes pop before the cable starts to burn.
What's the writing on the thick cable? If it's around 10mm2 cable and leads direct to the battery, it'd be a good candidate for a dc-dc charger imo. If it's below 6mm2 you'll probably need to replace it.

 

[Dellmassive]

that's the factory feeds to the underseat fuse box / towing fuses power prep work.

its normal fed from the SA fuse box under the battery with a 100A fuse. . .


have a look over this thread . . .

T6.1 battery removal / access Fuse Box SJ

I am in the process if planning a leisure battery install and dc-dc charger. However firstly I cant work out how to remove the battery to get access to the bulkhead grommets. Secondly is it possible to take power from the fusebox that is on top of the battery. I seem to have some of these unused.

www.t6forum.com

.

 

[Lukefx]

Thanks folks, I spoke to @travelvolts who supplied the battery and wiring, and he suggests not to use the factory auxiliary as if the fuse blows its under the battery so a pig to change.

 

[Dellmassive]

changing that fuse is a pain, thats true.

but you should never have to change it . . its a 100A main fuse.

just fit a 20-80A fuse at the seat end . . . then that will blow before the 100A.


(Edit- Basically the 20-80A fuse will blow if you have an issue with your installation. Then the 100A fuse will still blow to protect the cable in the event of catastrophic failure IE, vehicle collision that smashed the van and caused a dead short)

and install the job properly so you wont be blowing any fuses.

 

[laidbackian]

This is my Victron Orion-TR Smart install under the passenger seat, 95ah battery under the drivers seat. Works a treat and VictronConnect app is really useful.

 

[Soundz]

@Dellmassive..........Del seeing ian's lovely little orion install made me go back to a recent conversation ,with local auto sparky and also another installer and conflicting thoughts:

Dell Ii want to instal an Orion tr smart 12 12 30 non isolated, along with a whole host of other blue tack BMV 712'n' shunt 150watt solar panel an mppt. 75 /15 ( already doing it's thang ) 20A mains charger........ and 12 1200 inverter hopefully powered by roamer SB.

Specifically on the B2B 16mm2 cable ( max it will take) will be fused at both ends batt wise. My question and conflicting thoughts regard that fuse and it's size. The victron manual states 60A....one chap who has fitted loads uses 30A.he states the Orion is regulated so can't draw more than 30A.so if there's any probs the fuse blows as the weakest link ...all as it should be. Now the rule of thumb with fusing seems to be 1.25X amps in a circuit...and that basically is what the other installer does.using a 40A fuse

Del why are victron stating a fuse that's so much higher IE 60A.. what am I missing mate? ....From memory the max the TR 12 12 30 can output is around 35A....which I'd imagine the Roamer could ask of it. So my gut instinct is 30A fuse is a bit low ..( maybe that chap primarily works with lead acid?).....conversely the 60A seems on the high side....... I'm not a sparky but really want to understand as much as I can about my offgrid leccy system .and sure it's only a fuse. It's just I struggle when folks are making such different choices and want to get my head around why?

Ta muchly for any thoughts.install will be in a T5

stu