Alternators and DC to DC Chargers

[dcl129]

Is it safe to hook a dc to dc charger straight to a typical alternator without a starter battery in parallel? I am working on a bit of a weird project.

 

[boatbuilder]

It might be noisy. The battery will help filter noise as well as even out spikes.

 

[dcl129]

It might be noisy. The battery will help filter noise as well as even out spikes.

What can I use to filter the noise without a battery. Weight is one of my concerns and Lead Acid is heavy.

 

[boatbuilder]

You could try one of the larger filters for audio systems. Depends on what load you are powering. You can also use a power sports AGM battery. They are smaller and lighter than a full size battery. I have used them in places where I don't need a large amp-hr capacity.

 

[dcl129]

You could try one of the larger filters for audio systems. Depends on what load you are powering. You can also use a power sports AGM battery. They are smaller and lighter than a full size battery. I have used them in places where I don't need a large amp-hr capacity.

hmm. I guess it would make more sense if I give you a full rundown what I'm trying to accomplish. I am trying to make a overlanding vehicle and I do not want to use lead acid at all. I know creates complications for wiring and a 12 Volt power system. I want to be able to power items using an inverter and still be able to start my car after prolonged use. I know lifepo4 are problematic for alternators because of current draw, this is why you must have a in-between device to mitigate.

So, what are your thoughts to best tackle this with only using a DIY LIFEPO4? Is it smarter to just have a small AGM as a starting battery and noise filter? Do I run a separate wire for starter to LIFEPO4 and have alternator to converter to battery?

Please let me know where I need to start to have the least number of components/complexity?

To add I will be also installing a 12v sound system...Can I hook up to DIY LIFEPO4 in parallel with dc to dc converters?

Sorry for all the complexity and questions I'm new and really need help.

 

[Larry N.]

I am trying to make a overlanding vehicle and I do not want to use lead acid at all.

I'm not quite sure what that is, perhaps an off-road vehicle to get into rough areas? What kind of base vehicle are you starting with? Is it a van, or a pickup, or a small delivery truck, or what? This is important because it will dictate weight concerns, size of alternator, and other restrictions on what you can do.

I want to be able to power items using an inverter and still be able to start my car after prolonged use.

Your description sounds as if you want ALL of the 12V DC system to work together for both the chassis (vehicle) and for the "house" part, rather than having separate chassis DC system and house DC system, thus a battery (and alternator) for the chassis and a battery (or two or three) for the house the way most RVs do. Do you plan to be able to plug it into shore power, or strictly run off of the alternator on board, or perhaps you'll have a generator to provide power?

Will you have air conditioning or a microwave oven, or anything running on 120V AC power other than a stereo or TV through the inverter? You might mention what "items" you are wanting to power through the inverter -- that will let us have some idea of how MUCH power you'll need.

In other words, more information is still needed about what you're working with and what you intend to have on board.

 

[John From Detroit]

I would not recommend it. For one thing the alternator might refuse to alternate...er. work.
(Some will, some won't)

Also the alternator may output some rather strange voltages. (Not possible to tell without measuring and you need equipment that understands peaks not just averages.. Both digital voltmeters and analog may not give accurate readings.. a 'scope (oscilloscope) may be needed)

 

[Mark_K5LXP]

After reading through this thread the only conclusion I draw is that you're creating a complicated and expensive alternative for a single (durable) AGM battery.

Mark B.
Albuquerque, NM

 

[dcl129]

I'm not quite sure what that is, perhaps an off-road vehicle to get into rough areas? What kind of base vehicle are you starting with? Is it a van, or a pickup, or a small delivery truck, or what? This is important because it will dictate weight concerns, size of alternator, and other restrictions on what you can do.


Your description sounds as if you want ALL of the 12V DC system to work together for both the chassis (vehicle) and for the "house" part, rather than having separate chassis DC system and house DC system, thus a battery (and alternator) for the chassis and a battery (or two or three) for the house the way most RVs do. Do you plan to be able to plug it into shore power, or strictly run off of the alternator on board, or perhaps you'll have a generator to provide power?

Will you have air conditioning or a microwave oven, or anything running on 120V AC power other than a stereo or TV through the inverter? You might mention what "items" you are wanting to power through the inverter -- that will let us have some idea of how MUCH power you'll need.

In other words, more information is still needed about what you're working with and what you intend to have on board.

Ill be doing light overlanding/road triping (like rally without the racing). It will be a family sedan that is heavily modified with tires, roof rack,etc.

I was "planning" to have the alternator charge the lifepo4 through dc to dc chargers and of course have some type of monitoring via vitron to know when to stop using inverters so I can start the car. Or is it better to just use a small super lightweight battery in parallel right after the alternator?

I "plan" to just have a large tent, portable cooking appliances and other portable entertainment items.

Im a crazy person with hypothetical ideas haha.

 

[dcl129]

After reading through this thread the only conclusion I draw is that you're creating a complicated and expensive alternative for a single (durable) AGM battery.

Mark B.
Albuquerque, NM

AGM has no where near the runtime that lifepo4 has.

 

[dcl129]

I would not recommend it. For one thing the alternator might refuse to alternate...er. work.
(Some will, some won't)

Also the alternator may output some rather strange voltages. (Not possible to tell without measuring and you need equipment that understands peaks not just averages.. Both digital voltmeters and analog may not give accurate readings.. a 'scope (oscilloscope) may be needed)

Well wouldn't put a load device in-between fix this?

 

[Larry N.]

It will be a family sedan that is heavily modified with tires, roof rack,etc.

OK, that makes a BIG difference in what systems would be on board, how they fit, and what you can do. My first thought is that the LifePO4 makes a poor starting battery, and that in addition to the LifePO4 for use with an inverter and TV, stereo, etc. I'd think it better to just leave the car battery alone to work with the engine and car systems, instead using the LifePO4 and inverter as a separate system, perhaps tied in to alternator (and hopefully to shore power when available) for charging.

But at least folks can more readily target what you're trying to do, now that we know it's not an RV, even a homemade one, but is a car modification project.

 

[Lou Schneider]

How large of a battery are you making? If it's a nominal 12 volts and about 200 amp-hours or less, it will get along fine with your vehicle's charging system. I have a pair of Lion Safari UT-1300s at 100 amp-hours each and they charge just fine from the stock charging system in my Trek motorhome. The UT-1300s draw 30 amps each from the alternator from empty to full, or 60 amps for the pair. If your alternator will handle this you're good. You only need a DC-DC charger if this is too much load for your alternator to handle.

My system is simple - a relay cross-connects the house and starting batteries when the engine is running and the alternator charges both at the same time. I can also press a "boost" switch on the dash to do the same if the chassis battery is low. This came in handy on my first trip out when the starting battery died in the middle of Nowhere, NV. It had an internal open so it was completely out of the circuit. The two UT-1300s started the Chevy big block V-8 just fine when I pressed the boost switch and let me put off replacing the chassis battery until I got home.

I'd use an AGM starting battery, something like the no-maintenance Optima. Simple and effective. Then build out your Lithium house system and use the relay described above. You'll always have the starting battery ready to start the engine no matter how far down you draw the house lithiums.

 

[John From Detroit]

Well wouldn't put a load device in-between fix this?

Likely no the output of an alternator is unfiltered rectifited multi phase AC. it needs not a load device but a "filter" device before you feed it to electronics like the DC/DC converter.
One issue is the peak voltage (unflitered) can be rather hight. way more than 12 volts.

 

[dcl129]

OK, that makes a BIG difference in what systems would be on board, how they fit, and what you can do. My first thought is that the LifePO4 makes a poor starting battery, and that in addition to the LifePO4 for use with an inverter and TV, stereo, etc. I'd think it better to just leave the car battery alone to work with the engine and car systems, instead using the LifePO4 and inverter as a separate system, perhaps tied in to alternator (and hopefully to shore power when available) for charging.

But at least folks can more readily target what you're trying to do, now that we know it's not an RV, even a homemade one, but is a car modification project.

I get you on using as a separate system with using regular battery in inline.

I may be wrong but lifepo4 prismatic cell can do up to 3C continuous with more peak. That can turn over starter easily especially in parallel.

 

[dcl129]

How large of a battery are you making? If it's a nominal 12 volts and about 200 amp-hours or less, it will get along fine with your vehicle's charging system. I have a pair of Lion Safari UT-1300s at 100 amp-hours each and they charge just fine from the stock charging system in my Trek motorhome. The UT-1300s draw 30 amps each from the alternator from empty to full, or 60 amps for the pair. If your alternator will handle this you're good. You only need a DC-DC charger if this is too much load for your alternator to handle.

My system is simple - a relay cross-connects the house and starting batteries when the engine is running and the alternator charges both at the same time. I can also press a "boost" switch on the dash to do the same if the chassis battery is low. This came in handy on my first trip out when the starting battery died in the middle of Nowhere, NV. It had an internal open so it was completely out of the circuit. The two UT-1300s started the Chevy big block V-8 just fine when I pressed the boost switch and let me put off replacing the chassis battery until I got home.

I'd use an AGM starting battery, something like the no-maintenance Optima. Simple and effective. Then build out your Lithium house system and use the relay described above. You'll always have the starting battery ready to start the engine no matter how far down you draw the house lithiums.

Its a toyota 150amp alternator plan on upgrading to a mechman 250amp alternator.

Also will be a 100ah prismatic in parallel to 200ah 4sp2.

What you doing in middle of nowhere, NV at the Pb dump site? haha You did this with straight lifepo4 parallel to AGM jump start? Is your lifepo4 DIY? Nice set up btw.

I might just have to do a dual battery system indeed. i have an yellow top optima but still too heavy. Im thinking super small and light of the shelf 20ah AGM with 400cca with DIY house separate?

Should i be getting non-isolated or isolated charger?

 

[dcl129]

Likely no the output of an alternator is unfiltered rectifited multi phase AC. it needs not a load device but a "filter" device before you feed it to electronics like the DC/DC converter.
One issue is the peak voltage (unflitered) can be rather hight. way more than 12 volts.

You don't think DC to DC converters isn't enough internal resistance to make newer car alternators think it a Pb battery and alternator will deliver what every the converters are asking at the time?

 

[John From Detroit]

You don't think DC to DC converters isn't enough internal resistance to make newer car alternators think it a Pb battery and alternator will deliver what every the converters are asking at the time?

That is not the issue, the issue is the alternator output is raw, unflitered, rectified AC. and can easily peak at over 100 volts (well over) this can damage the DC/DC converter if it's not designed to take that kind of input.

 

[Old_Crow]

My son has an ambulance converted into a camper. His 110v supply is a self contained unit that has it's own Lithium battery and charging system. He can charge it either off a suitcase solar setup or if there's shore power available. He says you can also plug it into the lighter socket and charge it off the alternator.
This may be way overkill for your application, but they make smaller units. Why waste all this time doing the engineering, when it's already been done for you?

Goal Zero Yeti 1000X Portable Power Station

 

[dcl129]

That is not the issue, the issue is the alternator output is raw, unflitered, rectified AC. and can easily peak at over 100 volts (well over) this can damage the DC/DC converter if it's not designed to take that kind of input.

If the DC to DC converter is not designed to handle that what would be your solution to fix this problem?