7 replies to this topic

[LAWNMOWERMAN]

https://www.12voltpl...lternators.html

 

This article is very interesting.I am using a voltage sensing relay(VSR) to power my DC-DC charger and now I know why that is not a good idea. My 2017 Tacoma has smart alternator.I will be removing the VSR and use an ignition trigered power source to power my DC-DC charger.

[rando]

I am not sure there is actually a problem here - at startup the alternator will always be >> 13.0V which is what the blue sea ACRs need to combine.  You may not get a whole lot of charging from the alternator if the ECU cuts back the voltage, but your DC-DC should take care of that. 

 

My ACR works just fine with my Tacoma smart alternator. 

[larryqp]

I have a 2016 Ford F150, with a smart alternator and my 2019 FWC Hawk has a Blue Sea 7611 Auto Charging Relay with Aux Battery priority. During every trip I've taken, plus leaving my National Luna 50L Refrig/Freezer on all the time, I have never had a problem with getting my 2 x 6 volt 260 amp hour AGM batteries to 100% charge........ until this last trip.

 

In past trips I would drive to a location, such as Big Bend NP in the winter, or some high elevation mountain spot in Colorado and then only drive short distances to a trail head or fishing spot. The truck would sit most of the day in full sun and the 2 x 100 watt Renogy solar panels would fully charge the house batteries. When parked at home, the truck is in full sun and the batteries stay at 100%

 

This last trip I did about 400 miles on the IDBDR, so I drove most of each day, often in the forest and didn't setup camp until around 4pm. My batteries never got to 100%, so now I'm convinced I need a DC to DC charger. I never saw the need for one before this trip.

 

 I'm thinking about getting Renogy's 20amp unit, it's reasonable and I'm assume if I drive for 5 hours it will yield 100 amps into my batteries which is more than I use in a day. So I have some questions for the electronic wizards in the group.

 

1- Is my math correct, will 5 hours of driving with a 20 amp DC to DC charger give me 100 amps?

 

One of the advantages of the 20 amp unit over a 30 amp or 40 amp unit, is that according to their website, with the 20 amp unit, Renogy specs out 8 AWG copper wire for runs 11- 20 ft from the starter battery and 10 - 8 AWG for runs 11- 20 ft to the house battery. (My current wiring done by the Montana FWC is 10 AWG. ) Their website also says to place the charger close to the starter battery, but reading this forum it appears most people mount the charger in their camper. 

 

2- Does the DC to DC charger replace the Blue Sea 7611? 

 

3- If the DC to DC charger doesn't replace the Blue Sea 7611, then does the charger get wired before the Blue Sea unit?

 

Thanks in advance.

Edited by larryqp, 16 July 2021 - 11:02 PM.

[Jon R]

Question 1: yes a 20 amp charging source running for 5 hours will nominally add 100 amp-hours to your stored energy, assuming the battery isn’t topped off before 5 hours.

Question 2: the dc to dc chargers I’ve researched all function as a battery isolator when the truck is shut down. However, in some situations where voltage drop is fooling the charger into detecting engine not running when in fact it is running, one way to solve that could be to force the dcdc charger to be always on and use an isolator relay on the truck side. That’s probably not the best way to solve that problem, though. I think most people remove their isolator when they get a dc to dc charger.

Edited by Jon R, 17 July 2021 - 02:13 AM.

[Jon R]

Also, Renogy’s recommendation to put the charger close to the charging source defeats one of the main advantages of a dc to dc charger, which is to compensate for voltage loss in the source wiring and thereby provide proper charging voltage to the camper battery at the rated current. That advice is likely given because they have a very simple engine running detection scheme that can’t function properly with typical voltage drop if located at the camper battery, which is really where you want it. I would make sure I fully understood the engine running detection logic before buying that charger. You do want the charger at the camper battery, and if it won’t work there I’d buy a different product.

Edited by Jon R, 17 July 2021 - 02:28 AM.

[larryqp]

Thanks Jon R,

I am now thinking of the Victron Orion-TR Smart 12/12 - 18 Amp Isolated DC-DC charger. For another $100 in does not require an additional wire to sense engine on and it has built in blue tooth. I don't think the 18 Amp vs 20 amp is significant for me but the Victron unit seems to be a better product and having bluetooth to monitor with my phone seems beneficial.

[kmcintyre]

Thanks Jon R,

I am now thinking of the Victron Orion-TR Smart 12/12 - 18 Amp Isolated DC-DC charger. For another $100 in does not require an additional wire to sense engine on and it has built in blue tooth. I don't think the 18 Amp vs 20 amp is significant for me but the Victron unit seems to be a better product and having bluetooth to monitor with my phone seems beneficial.

That's what I'm using and from quite a few sources, the Victron was claimed to be a superior product in every case.

[Jon R]

I have the Orion 12/12-30 isolated charger and it is working for me with no problems. The bluetooth interface is nice. I have a crew cab long bed full size truck with a Grandby so the wire run to the camper battery is nearly 30 feet. I used 6 awg wire and have a little over 1 volt drop at 30 amps. If you have a large voltage drop due to small wire gage the Orion can still handle it but it will cycle off briefly every two minutes to check if the engine is still running. I wanted to avoid that so I used 6awg. 8 awg might also have been adequate to avoid the test cycling. I suspect the voltage drop with 10 awg would trigger the engine running test cycling. Again, the cycling is not a problem - I just wanted to avoid it. The Orion 30 amp version puts out quite a bit of heat when it operates, so make sure you follow the recommendations on space and ventilation.