Hi, I'm having trouble finding in-depth information on the DC to DC battery charger. I have a 180 amp alternator (ProMaster 2500) and I'm wondering if the Renogy 60 amp DC to DC battery charger will work okay? I haven't been able to find specs on exactly how many amps the alternator actually puts out. Is there any reason not to use the 60 amp charger?
12V 60A DC to DC Battery Charger
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John Frum
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A 180 amp alternator generally only puts out the rated amps at impractically high rpms.
If you can find a part number you can probably find a graph of rpm vs amperage.
If it was me I wouldn't engage the dc to dc charger until the starting battery had time to top off and the engine was up to road speed.
I would do a manual switch like this the guy.
The draw back is you need to remember to turn it on and more importantly turn it off.
If you could had a circuit that closes when the transmission is in Drive that would probably suffice.
If you have a shunt you can test and see what you get based on rpm and the depth of discharge of the house batteries.
If you can find a part number you can probably find a graph of rpm vs amperage.
If it was me I wouldn't engage the dc to dc charger until the starting battery had time to top off and the engine was up to road speed.
I would do a manual switch like this the guy.
The draw back is you need to remember to turn it on and more importantly turn it off.
If you could had a circuit that closes when the transmission is in Drive that would probably suffice.
Thanks for this! I guess I'm worried that if it's trying to pull more power than the alternator can provide will it cause damage to the alternator? Or is this DC-DC charger able to manage this OK?
My understanding is around 30-50 amps is a more realistic alternator output to the charger.
John Frum
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Update to previous post.
I didn't explain myself well.
If the batteries are trying to draw the full 60 amps and your alternator is not able to supply 60 amps(engine at low idle).
The alternator is going to be stressed and doubly stressed because its not going to be able to cool itself at low rpm.
I didn't explain myself well.
If the batteries are trying to draw the full 60 amps and your alternator is not able to supply 60 amps(engine at low idle).
The alternator is going to be stressed and doubly stressed because its not going to be able to cool itself at low rpm.
John Frum
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I think you are guessing correctly.
Got it, thanks! I have a clamp meter on the way.
Trying to understand if a 60 amp rating means it'll take the full 60 only if it's there so the alternator isn't stressed, or if it tries to pull the full 60 regardless of whether it's getting less, which cause stress on the alternator.
I'm also wondering why Will recommends sticking with a 20 amp DC-DC Renogy charger when places like AM Solar recommend much larger Sterling DC-DC chargers (like 120 amp).
I'd also love to see Will review Sterling DC-DC chargers.
Trying to understand if a 60 amp rating means it'll take the full 60 only if it's there so the alternator isn't stressed, or if it tries to pull the full 60 regardless of whether it's getting less, which cause stress on the alternator.
I'm also wondering why Will recommends sticking with a 20 amp DC-DC Renogy charger when places like AM Solar recommend much larger Sterling DC-DC chargers (like 120 amp).
I'd also love to see Will review Sterling DC-DC chargers.
I haven't been able to find the specs for my exact alternator although other similar models around the same rated amperage appear to put out around 100 amps when hot (200F/93C) at 2250 alternator rpm (3:1 ratio with engine RPM at 750 - which I think is around idle?) & 146 amps at 7500 alternator rpm. The amps are higher at lower temps.
I'll have a play around when the clamp meter comes. I wonder how many spare amps there are after the starter battery is fed with its loads met.
I'll have a play around when the clamp meter comes. I wonder how many spare amps there are after the starter battery is fed with its loads met.
mapguy525
Solar Enthusiast
Difficult to help without more info on your system and the specific alternator.
Most non-HD automotive alternators have very low duty cycles. The graphing/documentation SmoothJoey references will help understand output and duty cycle on the specific alternator.
The challenges of alternator charging are discussed very well on the Marine How To website:
https://marinehowto.com/lifepo4-batteries-on-boats/
Search on "Alternator Protection Devices". This will get you directly to solutions, but to understand the full implications of multiple charge sources read and analysis the whole article.
This website is a very good reference on implementation challenges of LFP installs that have multiple charge sources.
Most non-HD automotive alternators have very low duty cycles. The graphing/documentation SmoothJoey references will help understand output and duty cycle on the specific alternator.
The challenges of alternator charging are discussed very well on the Marine How To website:
https://marinehowto.com/lifepo4-batteries-on-boats/
Search on "Alternator Protection Devices". This will get you directly to solutions, but to understand the full implications of multiple charge sources read and analysis the whole article.
This website is a very good reference on implementation challenges of LFP installs that have multiple charge sources.
I'll keep digging to find the exact specs, I have a 2020 Ram ProMaster 2500 with the stock 180 amp alternator.
I also have a clamp meter on the way to do some tests at home. Looking at comparable 160-190 amp alternators there should be 100+ amps available, plus I'll have a manual switch to only activate DC-DC charging on highways.
System wise, I'm looking at the following:
Victron SmartSolar MPPT 100/50
Victron Multiplus 3000W 12V Inverter/charger
4x 150W solar panels
4x 100Ah 12V LiFePO4 (DIY) batteries OR 2x 190Ah 12V LiFePO4 (DIY) batteries (wired in parallel - ensuring combined BMS amperage suitable for 3000W inverter)
Victron BMV-712 battery monitor
Sterling 60amp 12V DC-DC charger
The solar can produce 50 amps and the DC-DC 60 amps, so 110 amps together (assuming 100% efficiency to be safe).
As for loads, we have kids so our use will be heavier than most, thus the big battery bank and inverter. I plan to have a 1400W electric water heater and 1800W bench top convection oven. Water heater possibly used 1hr every couple of days and the convection over maybe 20 minutes every couple of days. Otherwise we both have laptops for work and the usual small electronics (phones etc).
I also have a clamp meter on the way to do some tests at home. Looking at comparable 160-190 amp alternators there should be 100+ amps available, plus I'll have a manual switch to only activate DC-DC charging on highways.
System wise, I'm looking at the following:
Victron SmartSolar MPPT 100/50
Victron Multiplus 3000W 12V Inverter/charger
4x 150W solar panels
4x 100Ah 12V LiFePO4 (DIY) batteries OR 2x 190Ah 12V LiFePO4 (DIY) batteries (wired in parallel - ensuring combined BMS amperage suitable for 3000W inverter)
Victron BMV-712 battery monitor
Sterling 60amp 12V DC-DC charger
The solar can produce 50 amps and the DC-DC 60 amps, so 110 amps together (assuming 100% efficiency to be safe).
As for loads, we have kids so our use will be heavier than most, thus the big battery bank and inverter. I plan to have a 1400W electric water heater and 1800W bench top convection oven. Water heater possibly used 1hr every couple of days and the convection over maybe 20 minutes every couple of days. Otherwise we both have laptops for work and the usual small electronics (phones etc).
You might check out the Promaster forum for info about the alternator. Even though they will try to talk you into using lead acid batteries, they last a long a time if you only draw them down by 20% and are able to fully charge them almost every single day, which is a totally realistic usage scenario for most people.
One thing to consider is that the Renogy chargers seemed to be rated on output, at least people have reported that the 50A charger outputs 50A amps so presumably it's drawing more than that from the alternator.
One thing to consider is that the Renogy chargers seemed to be rated on output, at least people have reported that the 50A charger outputs 50A amps so presumably it's drawing more than that from the alternator.
Hey not sure how useful this is, it I prefer instant gas hot water, we use a gas over, gas grill, gas cooktops. I try to run a 12v van except for the necessary 240v (aus) appliances like laptops. Gas is great!
Good suggestion but we're traveling with young kids so the wife prefers no gas since it's a DIY job (and paying someone to install & run gas lines bumps up cost outside of DIY territory). Plus I want to keep the van as stealth as possible so I didn't want to install any wall vents for a gas water heater (since it's an indoor shower).
Please also consider:
- Your alternator supplies power to other devices, such as charging your starter battery, heated seats, windscreen, stereo etc. If you start pulling 60 or more amps from it just to charge your house battery you might end up overloading it.
- Your battery's BMS will have a current rating too, and most people under-rate them for safety. A 'typical' BMS for a 100AH LiFePO4 battery is 100A, most people de-rate to say 60A. Push 120A and you'll let the factory-supplied magic smoke out.
Electric Personality
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My guess is you will regret 120 amp.
I have a new F150, and am sticking with 20 amp. At highway speed it is only turning 1500 rpm.
I have a new F150, and am sticking with 20 amp. At highway speed it is only turning 1500 rpm.
Prefersdirt
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Interesting thread. I have been wondering about DC to DC charging for a backup battery bank, vs going through a traditional genny.
