# Charge a 48 volt (4x12v) battery bank with a 12 volt charger. Possible?

#### Thick8

Joined Sep 16, 2017
10
I have a 12v/120a CNG generator, 8 8D deep cycle batteries, and a 10,000 watt 48v DC to 230v AC split pure sine wave inverter.
My current setup to run my garage is the 8 batteries wired in parallel running both a 5000w and a 1800w modified sine wave 12v inverter. Works good but I was just given the generator and 48v inverter.
I'm trying to draw up the charging circuit so I can make this a whole house system that I can add solar panels to at a later date. I'm thinking simple high amp diodes wired into the charging circuit should work but my diagram is confusing me. I have a pile of 85a alternators I can strip the diodes from.
Can anyone help?

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#### tcmtech

Joined Nov 4, 2013
2,867
Unfortunately you cant charge a 48 volt system with a 12 volt input using any combination of diodes. You need to either do each battery one at a time or use some sort of voltage boosting circuit.

#### Thick8

Joined Sep 16, 2017
10
Seeing as how you have reached the rank of "Distinguished Member" I guess I have my answer.
Do you know of a highly efficient 12vDC to 48vDC converter?
Or is there maybe a way to turn a 12 volt 120 or 160 amp alternator into a 48 volt alternator? They are both HD truck APU alternators rated at the listed amperage continuous. The environment that I will have it in is much cooler than under the hood of a truck.

#### nsaspook

Joined Aug 27, 2009
8,513
My 2c but it won't be cheap.
I would keep the 12 volt system as is for now, sell the generator (if it's not needed for the 12vdc system), use the money to build-out the 48 volt house system with a compatible solar charge controller/battery bank and AC powered 48vdc battery charger that can be used with utility power or from the garage inverter until you have solar power.

#### tcmtech

Joined Nov 4, 2013
2,867
Seeing as how you have reached the rank of "Distinguished Member" I guess I have my answer.
Do you know of a highly efficient 12vDC to 48vDC converter?
Or is there maybe a way to turn a 12 volt 120 or 160 amp alternator into a 48 volt alternator? They are both HD truck APU alternators rated at the listed amperage continuous. The environment that I will have it in is much cooler than under the hood of a truck.
If it's built around a large truck alternator it's likely possible to reconfigure the alternator's windings to put out the 48 volts at ~1/4 the current. However to do so takes a bit of electrical knowledge to do the reconfiguration of the winding conections plus make the necessary circuits to allow for the voltage regulator to work properly.

#### Thick8

Joined Sep 16, 2017
10
The generator is a 6.5HP gasoline engine with a natural gas adapter (that I run off the NG house supply) that is paired with a 12v/120a HD truck alternator. I also have a 2 cylinder diesel 12v /160a HD truck generator (APU). As the APU would also run the trucks A/C system I think it would be overkill for my application. Plus I would have to maintain a diesel fuel supply tank for it. I also have a Honda GXV530 engine that I can convert to NG and use to spin a 48 volt alternator.
The inverter is an AIMS that is pretty much all inclusive for battery and generator input.
The solar array probably won't happen for a few years at least.

#### bassbindevil

Joined Jan 23, 2014
168
I'd think about belting 4 alternators off one motor, so each battery is charged properly.

#### bassbindevil

Joined Jan 23, 2014
168
Stupid editing time-out... I was going to add that some care would be needed to avoid shorts and shocks. So, maybe charge each battery in turn, using relays, or manually with PowerPole connectors.

Or better, surely there are battery balancing circuits for lead-acid batteries, so you could charge the whole string at once.

#### Thick8

Joined Sep 16, 2017
10
I'm hoping for a more "set it and forget it" option. The grid power goes out and the inverter kicks in and will automatically start and stop the generator to maintain full charge in the battery bank.

#### Thick8

Joined Sep 16, 2017
10
So a buddy of mine tells me to just plug a 48 volt golf cart charger in to the 120v output circuit to charge the batteries. There will be some energy loss but it shouldn't be that much. While it would work I think it would be extremely inefficient .

#### nsaspook

Joined Aug 27, 2009
8,513
So a buddy of mine tells me to just plug a 48 volt golf cart charger in to the 120v output circuit to charge the batteries. There will be some energy loss but it shouldn't be that much. While it would work I think it would be extremely inefficient .
It wouldn't be extremely inefficient, maybe an extra 10-15% loss vs direct conversion DC to DC. High power (>1000W) 12volt system can get lossy quickly unless you use massive cables for interconnects and then you have engines, driving truck alternators, that charge FLA batteries, that power AC inverters as another chain of inefficiencies.

#### tcmtech

Joined Nov 4, 2013
2,867
I'd think about belting 4 alternators off one motor, so each battery is charged properly.
The most practical would be to get a pair of 24 volt alternators that have independent positive and negative outputs and use a pair of them to charge the 48 volt bank as to 24 volts sets in series.

There are 48 volt alternators available but they tend to be hard to find and rather costly so doing some cost analysis to the concepts of how many alternators or to what modification you wish to pursue would be necessary.

Another option would be to tap into the AC output and use three 1:4 step up transformers to boost the AC output of the alternator's windings up and then rectify that to get the voltage you need.

There are a number of ways to do things but for the most part all of it is a matter of cost analysis and difficulty to build.

Joined Feb 20, 2016
3,885
I would be wary about charging with 2 x 24V alternators in series. The cases will have to be isolated unless you alter the wiring internally. Maybe having a go at rewiding one with more turns to make it a 48V one?
The best is to aim for a 48v charging system. You could look at something like this...
http://www.ebay.com.au/itm/1pcs-Boost-DC-DC-Converter-Power-Supply-Step-up-Module-10-60V-to-12-80V-600W-IT/162034678644?_trkparms=aid=555019&algo=PL.BANDIT&ao=1&asc=20151005190540&meid=0abefeaa98044199b22314da6054427c&pid=100505&rk=1&rkt=1&&_trksid=p2045573.c100505.m3226
But as to the quality ??
Some hacking will be in order and will require a bit of electronic knowledge and care. Batteries can cause things to go bang and burn if you get things wrong. They are capable of supplying quite a lot of current. A bit of advice, wear safety specs!

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#### tcmtech

Joined Nov 4, 2013
2,867
I would be wary about charging with 2 x 24V alternators in series. The cases will have to be isolated unless you alter the wiring internally.
There are many 12 and 24 volt commercial alternators that come from the factory with both the postive and the negative isolated from their cases.

As for changing the output on a larger commercial unit that's not terribly hard and does not require rewinding being they are typically wound with multiple winding sets in parallel for each phase play for a higher current 12 or 24 volt unit most are configured in a three phase Delta setup which when rewired to a Wye configuration and the parallel winding sets are put in series getting way higher voltages out of a stock stator is rather easy.

The only real issue at that point is keeping the stock regulators input voltage the same while making it think the higher voltage is the the one it should be seeing. In the case of the OP that may be as simple as disconnecting the internal power feeds plus voltage sensing circuits going to the regulator from their internal sources and moving them to an external point like feeding off of and sensing the first 12 volt battery (for a modified 12 volt alternator) or the second battery (for a 24 volt alternator) while putting the actual 48 volt power output to the two or three upper batteries above it/them in the set of four.

Many of the larger frame heavy commercial application Leece Neville and Prestolite alternators come with isolated output plus in stock configurations that include 48 volt and or even multi volt output designs.

http://www.prestolite.com/literature/stm/PP-1184-US_Quick_Reference_Guide-lo-res.pdf

Most any dealer that carries either line can get the 48 volt units but figure one might cost $100+ over what the same unit in 12 or 24 volt configuration costs. However Is see many online sources carry them in stock and a 48 volt 30 - 50+ amp alternator can be had for around$300 -$350. 48 Volt 60 Amp Leece Neville/Prestolite Alternator. http://www.prestolite.com/pgs_products/specs.php?item_detail_id=141&item=A0014413AA ^New ~$400^
https://www.finditparts.com/product...jiFgA-TcG8nnPnXKuUD1_i1jDqq85sMhoCZaAQAvD_BwE

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#### ian field

Joined Oct 27, 2012
6,539
I have a 12v/120a CNG generator, 8 8D deep cycle batteries, and a 10,000 watt 48v DC to 230v AC split pure sine wave inverter.
My current setup to run my garage is the 8 batteries wired in parallel running both a 5000w and a 1800w modified sine wave 12v inverter. Works good but I was just given the generator and 48v inverter.
I'm trying to draw up the charging circuit so I can make this a whole house system that I can add solar panels to at a later date. I'm thinking simple high amp diodes wired into the charging circuit should work but my diagram is confusing me. I have a pile of 85a alternators I can strip the diodes from.
Can anyone help?
Anything is possible - there's various ways of going about it. Switching all the batteries from series to parallel for charging is complex and likely to be expensive. Flyback boost would certainly be easier, if you need a lot of charge current; you may have to start thinking along the lines of a push pull forward converter and step up transformer.

#### tcmtech

Joined Nov 4, 2013
2,867
Anything is possible - there's various ways of going about it. Switching all the batteries from series to parallel for charging is complex and likely to be expensive. Flyback boost would certainly be easier, if you need a lot of charge current; you may have to start thinking along the lines of a push pull forward converter and step up transformer.
Yep. Theres a number of ways to approach things but the way I see it is that if a person can afford to have eight 8D deep cycle batteries laying around they can easily afford the proper 48 volt alternator to keep them charged.

I don't know what the OP paid for his but the last time I priced one out for someone they were pushing the $350 -$400 mark provided a I had a same sized core to give back for the \$50 core exchange fee.

12 volt 250 - 275+ Ah batteries are not cheap!