DC to DC charger question

[Falkend]

So I just installed Renogy's DC to DC Charger because the solar definitely won't cut it during the winter months. It works but I noticed my starter battery is only reading about 12.7 volts while the van is idling. The aux battery reads 13.7 at the same time.

When I unplug the system and run the van, the starting battery is at 13.7 while idling.

Anyone know how to both charge my auxiliary battery and make sure my starting battery is getting charged enough?

Do I need to upgrade my alternator? OR upgrade the alternator wiring?

thanks you.
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1984 Westy

[outcaststudios]

questions:

what dc to dc charger (amps?)

what gauge wire are you using?

what type of aux battery? deep cycle?

is teh renogy set for the correct type of battery?
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'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[Falkend]

[Schuylersister]

So the DC TO DC charger you installed is not a solar charger too?
Renogy makes two chargers with solar: DCDC30S and DCDC50S.
Which DC to DC charger did you use and how are you dealing with a solar charge controller?

[Falkend]

[outcaststudios]

do you have a temperature monitor on it? how is its D wire connected?

edit , nevermind i see that now. i would check to see if the green light is lit when the ignition is switched off just to eliminate it being on while the key is off. otherwise i would take a reading from the charger while it is switched on and confirm its numbers. its probably the fact that when you take the reading its while your vehicle is at idel, try revving it over 2500-3000 rpm and see if its charging at more than 12.7 v
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'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[Falkend]

[DanHoug]

to know what is really going on you need current monitoring in the line to the aux batteries. what is LIKELY going on is that the lithium batts are not finished charging so there is a significant current draw from the starting battery/alternator-- more than can be supplied at idle. this isn't really a problem at all because how much time do you spend idling? raise the rpm to 2500 rpm and what is the starting battery voltage? it is likely fine and will charge both battery sets while driving.

older BMW motorcycles are notorious for DIScharging at idle and not really putting juice back into the battery until 1800-2000 rpm.

personally, i would not upgrade the charging system until proven to be a failure. just remember to not sit there idling for really extended periods when your aux batteries have been previously drawn low. management through behavior vs upgrades.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[outcaststudios]

wait so when you take a reading from your battery while its above 2k rpm you still get no change? that doesnt sound right. have you checked your alternators output? it should increase to 13v or at least 12.9 regardless of that renogy issue. is it charging?
_________________
'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

https://www.thesamba.com/vw/classifieds/detail.php?id=2573791

[Falkend]

[Schuylersister]

I don't know if this helps but I recently had a new (rebuilt) Bosch alternator installed as well as the alternator upgrade wiring from GW. I was using a SurePower isolator at the time to charge my house battery (LA). The charging rate on the starter battery was barely 12.7 at idle with the isolator installed so I removed it. The charge rate on the starter battery now is 13.4-14.1.
I bought the Renogy DCDC30S and will install it soon. I believe it won't even charge the lithium house battery unless the voltage is 13.2 at the starter battery. I avoided ordering the DCDC charger you have because it didn't have those voltage limits.
Sure do hope you get to the bottom of it and let is know what happened.

[MarkWard]

Hello, the D+ terminal of the Renogy is not exactly accurate for the vanagon. It just needs to see power when the engine is running. Have you verified the green LED on the renogy is lit when the engine is running. I got a little creative for my D+ connection. I connected it to my X circuit so that during cranking it was disabled. Wanted to ensure the dc charger was isolated during cranking. I thought about it a little more and added a toggle switch and LED that controls the D+ circuit. Decided i didn’t always want the Renogy powered up. After a night of camping, the lithium SOC is 100% within an hour. Figured no sense running it each time the engine is running.

My battery BMS has Bluetooth so I can see the Amps in and out as well as the SOC on my phone.
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[Falkend]

[MarkWard]

I don't believe the Renogy dc charger has blue tooth built in. My actual battery BMS has bluetooth built in. So, I'm monitoring the battery. The app lets me see the amps in and the amps out to the battery.

I wasn't comfortable using the van's D+ alternator circuit. From memory, key on 12 volts is sent down the D+ circuit to excite the alternator into charging. Once the alternator starts charging, charging voltage is then sent the opposite direction from the alternator. This is what shuts the warning light off.

I wasn't sure how the Renogy would handle that and could not get a clear answer from them. In theory, the Renogy would power up when you turned the key to the run position which is not ideal because the D+ circuit would get hot. I just did not spend the time to work that out. Decided the X circuit was a better way to go. It cuts during cranking which is when you wouldn't want the Renogy combined. Plus, I'd rather have the van's starting circuit back up to spec after starting before combining. The toggle gives me that control. The LED is on the output of the toggle so if the toggle dies I have an indication. I have forgotten to turn it on though. Not the end of the world since we don't use much power camping.
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[shagginwagon83]

I had the Renogy 40a unit. It was set to turn on with my ignition. I never really had any issues cranking.

You could do an experiment and see how fast the charger starts working with your BMS.
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Brandon
"Jo Ann" - '83.5 Westfalia EJ22e w/Peloquin
Instagram @joannthevan

[MarkWard]

Our van at times is a daily driver. I just did not see the point of the Renogy having to power up each time the engine was running. In daily use, the accessory battery sees no load so it's SOC remains at 100%. Road trips are another story. Once the battery is at 100% SOC after a night of camping, don't see the need to have the Renogy powered up all day long. Having the starting battery recover from starting and letting the alternator come up to temp before having to recover the Lithium was just an add on feature of having a toggle added. No science to back up that thought though.
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[Falkend]

[montanasurfer]

This is wild! I love how the samba reveals folks having similar issues/observations with such good timing. I just installed the 20amp version (https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/) and had the exact same situation happen!

Falkend, it sounds like we wired ours up the same way as well. I was basically converting the GW AUX kit to work with this charge (https://gowesty.com/products/basic-auxiliary-battery-install-kit-air-cooled-camper-non-campers). Basically just deleting the solenoid.

I will say that before I did this upgrade, I saw my alternator and starting battery around 14.1v.

Any logic behind why there is a change when adding this dc to dc?
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1987 Vanagon GL - Wolfsburg Edition

[MarkWard]

You should have the same voltage measured at the alternator post, the starter battery post and the charger input terminal. Any difference is due to a voltage drop from resistance somewhere in the circuit. There was a recent thread about where to connect the dc input lead to. There are 3 good places. The alternator stud, the starter solenoid bat stud, or the positive terminal of the starter battery. You need to also pay attention to the distance and wire gauge. The manual spells this out. I'd be hesitant to use the vans factory wiring if you want full voltage and are seeing a drop.

The D+ voltage input is not as critical. It is just energizing the renogy to turn on. Like how a relay works. The output voltage of the renogy is set with the dip switches. You want those to match your battery ideal charge voltage.
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[fxr]