Options to charge 48v battery bank from 24v alternator

[drewlox]

Hello All,

New to the form here, appreciate any guidance with this topic.

I've got a 91 Prevost motorhome, it has a large 270amp, 24v alternator (most of which is not being used as both Cruiseair AC units have been removed). I'm adding a solar setup with roughly 15kwh of 48v batteries.

My issue is this, I'd like to be able to charge the 48v batteries while the engine is running. I've been looking everywhere and seem to have only found 1 solution (24V volt to 48 volt DC/DC converters (common negative) 1400 Watts Robust, marine, heavy duty from PowerStream.) but it's rather costly and I was hoping some of you folks might have some more suggestions.

Thanks in advance.

 

[Gary RV_Wizard]

The only alternative to a DC-DC converter I can think of is a 24v inverter feeding a 48v charger. That's electrically less efficient due to the power loss in inverting and then re-converting, but might be less expensive components.

 

[solarman]

Hello All,

New to the form here, appreciate any guidance with this topic.

I've got a 91 Prevost motorhome, it has a large 270amp, 24v alternator (most of which is not being used as both Cruiseair AC units have been removed). I'm adding a solar setup with roughly 15kwh of 48v batteries.

My issue is this, I'd like to be able to charge the 48v batteries while the engine is running. I've been looking everywhere and seem to have only found 1 solution (24V volt to 48 volt DC/DC converters (common negative) 1400 Watts Robust, marine, heavy duty from PowerStream.) but it's rather costly and I was hoping some of you folks might have some more suggestions.

Thanks in advance.

there are many industrial 24 to 48 V boost converters, however, you require a battery charger not a regulated power supply. certainly all of the industrial models I know of are just regulated power supplies, the more expensive of them ( as you have established ) do have adjustable voltage and current limiting that could be used as a charger for Lithium ( fixed voltage output with current limit set to a reasonable value ) the only reasonable ( and affordable ) solution I can suggest is same as Gary, use an inverter and a battery charger.. the cost of both those items will be considerably less than an alternative approach.
the other consideration of efficiency can be considered moot as, unlike solar, you have an "unlimited" so to speak, source of power as you drive during the day..

 

[drewlox]

Thanks for the info guys, never thought of that. Thanks @Gary RV_Wizard and @solarman.

Do you guys have any suggestions for a specific pairing of the inverter and charger? Victron?

 

[solarman]

Thanks for the info guys, never thought of that. Thanks @Gary RV_Wizard and @solarman.

Do you guys have any suggestions for a specific pairing of the inverter and charger? Victron?

that's down to price, what is your budget for this ?

if you keep the charging wattage below 1000 Watts, equipment is considerably less expensive..

you will need 3 items

1. inverter, 24 V to 120 V 1200 watts
2. 48 V charger
3. battery isolator/relay powered from ignition


Does that bus have a 24 Volt system as standard or is the 24 V specifically for the a/c units ?

 

[Utclmjmpr]

Might be cheaper to replace your alternator with a DUVAC type that will charge 24 and 48 volts simultaneously while keeping the two isolated...>>>Dan

 

[Utclmjmpr]

I have such a system on my American Coach,, the 12volt side for the house and 24 volts for the start batteries,, made by Leech Neville and common in large class "A" trucks..>>>Dan

 

[solarman]

that would be a good solution, i'm just suggesting solutions with the op's current hardware.

if he were open to replacing the alternator then there are many choices to new charging systems. there are multiple vendors with external dedicated battery charging modules that would give 48 Volts at several killowatts..

 

[Mark_K5LXP]

This is soundly into the nerdy/DIY realm but one idea I've tossed around is to use an alternator sans regulator, which will put out whatever voltage you want based on the field current you supply. There are numerous sites online that document modifying auto alternators for 120VAC. Most "universal input" (85-264VAC) switching supplies will accept a range of AC frequencies and some DC. All modern converters are switching supplies, and I've run 3 different ones with DC input. So if one already has a converter to charge house batteries and isn't fussy about input voltage or frequency, the only new thing to come up with is a circuit to regulate the field current to keep the alternator output within range of the converter input.

Mark B.
Albuquerque, NM

 

[solarman]

This is soundly into the nerdy/DIY realm but one idea I've tossed around is to use an alternator sans regulator, which will put out whatever voltage you want based on the field current you supply. There are numerous sites online that document modifying auto alternators for 120VAC. Most "universal input" (85-264VAC) switching supplies will accept a range of AC frequencies and some DC. All modern converters are switching supplies, and I've run 3 different ones with DC input. So if one already has a converter to charge house batteries and isn't fussy about input voltage or frequency, the only new thing to come up with is a circuit to regulate the field current to keep the alternator output within range of the converter input.

Mark B.
Albuquerque, NM

quite so, field winding control is the basis for these commercial modules. The big question here is if the typical "el cheapo" RV converter would be happy with such an input. ?
most common alternators are wired as a three phase Y configuration with diodes. I would be interesting to replace the diodes with a higher voltage type and then add a simple voltage controlled current source to power the field winding in a feedback loop to regulate the output voltage, add a simple micro to provide a charging algorithm and you have a nerdy 48 V battery charger.. LOL

 

[solarman]

48V alternator

 

[Mark_K5LXP]

The big question here is if the typical "el cheapo" RV converter would be happy with such an input. ?

One would have to either source a schematic to check the input circuit, or give it a smoke test but three different converters I've tried ran fine on DC input. So single phase AC or rectified 3 phase within the voltage range should both work fine. Wouldn't surprise me if there aren't retrofit/replacement regulator modules for any DC voltage you want for popular model alternators.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

I have such a system on my American Coach,, the 12volt side for the house and 24 volts for the start batteries,, made by Leech Neville and common in large class "A" trucks..>>>Dan

Dan, what year is your Tradition? My '04 Trad used a pair of 12v batteries for the chassis/engine but it was strictly a 12v system and the engine batteries were in parallel, not series. I'm pretty sure models back to at least 2000 were the same.

 

[Utclmjmpr]

Gary came off the line in June of 97,, titled and sold as a 98 as most were, with the Spartan MM chassis with IFS.. When I started to have trouble with the alternator I found that I had the DUVAC system,, one that I was not familiar with,, I had to study up on the system. It has been a fantastic coach and as trouble free as can be expected for the 14 years I have owned her..>>>Dan ( Only paid $28,100.00 for her at auction in 2008 and in great shape as a one owner bank repo.. Its first home was Albuquerque and to this day has no rust anywhere.)

 

[drewlox]

Thanks, everyone for the help... I think I'm now leaning toward a 48v alternator... although those balmar ones look nice, they come with a pretty price tag. I understand my situation is complex, and that usually means "specialized" equipment outside the norm. I have a pulley/wheel on the engine not being used that I could install the secondary alternator on, no problem. Now the fun part of figuring out what rpm will give me the amperage ideal for what I'm charging.

Although I still like the 24v Inverter to charger idea.... decisions, decisions....

 

[drewlox]

that's down to price, what is your budget for this ?

if you keep the charging wattage below 1000 Watts, equipment is considerably less expensive..

you will need 3 items

1. inverter, 24 V to 120 V 1200 watts
2. 48 V charger
3. battery isolator/relay powered from ignition


Does that bus have a 24 Volt system as standard or is the 24 V specifically for the a/c units ?

The bus comes standard with a 24v system. I'm not 100% sure but i don't think its specifically for the AC's. I believe it runs some of the engine management as well...

 

[House Husband]

Thanks, everyone for the help... I think I'm now leaning toward a 48v alternator... although those balmar ones look nice, they come with a pretty price tag. I understand my situation is complex, and that usually means "specialized" equipment outside the norm. I have a pulley/wheel on the engine not being used that I could install the secondary alternator on, no problem. Now the fun part of figuring out what rpm will give me the amperage ideal for what I'm charging.

Although I still like the 24v Inverter to charger idea.... decisions, decisions....

All alternators are rated at 6,000 RPM. So if you have a 3 to 1 drive ratio, the alternator will produce maximum capacity at 2,000 engine RPMs.

Richard