Safely charging a 24v eg4 RV LIPO with a vehicle 12v alternator

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I have an EG4 Lifepo4 24v 5.2Kwh battery in my Motorhome and wanted to get any advice on using a Victron Orion-Tr Smart 12/24-15 DC-Dc Non-Isolated charger. In Will's pros and cons of 12 or 24 volt systems he noted that he felt it unwise to try to charge off the vehicle generator unless it was changed to 24v. I am wondering if the victron unit came out after his video as it will draw 30 amps max from my 160amp alternator. Advice?

 

[Dzl]

I have an EG4 Lifepo4 24v 5.2Kwh battery in my Motorhome and wanted to get any advice on using a Victron Orion-Tr Smart 12/24-15 DC-Dc Non-Isolated charger. In Will's pros and cons of 12 or 24 volt systems he noted that he felt it unwise to try to charge off the vehicle generator unless it was changed to 24v.

What was his reasoning? Do you have a link to that video? I've never heard that before.

 

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The Video was:

, 12v vs 24v offgrid systems. His concern was over taxing your vehicle charging system and the necessity of complex equipment to do it and not backfeed when not charging. I think this victron unit accomplishes this. I have some question about "Isolated" vs "Non-Isolated". It seems the non-isolated are preferred opposite what I would think.

 

[Dzl]

His concern was over taxing your vehicle charging system and the necessity of complex equipment to do it and not backfeed when not charging.

It sounds like he may not have been that familiar with dc-dc chargers back then. For LFP you'll need the dc-dc (or an external regulator) one way or another even if the battery and the alternator are the same voltage, so sticking with the same voltage doesn't really eliminate any complexity with LFP from a system design standpoint.

Overtaxing the charging system is a real consideration, but then that is one of the main problems DC-DC chargers are intended to mitigate if sized properly for your alternator. I don't believe it should matter whether the DC-DC is 12-12, 12-24, or 24-24 so long as the max current is appropriate for your alternator and so long as you understand the input amps will be 2x the output amps with a 12-24 charger.

edit: its also possible his comments were meant in the context of high current charging only.

 

[mikefitz]

30 amps max from my 160amp alternator. Advice?

The Victron Orion is not 100% efficient, this with different SOC/voltage of either vehicle or service battery, results in the Orion taking up to 40 amps from the vehicle. This is not usually an issue as manufacturers specify around 50 amps as an allowable additional load.
Note with a non isolated charger the service battery negative must beconnected at some point to the vehicle chassis/metal body.
B2B charger, 12 to 12 , 12 to 24 , 24 to 12 volts, have been available for several years.

Mike

 

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Mike, it seems more appropriate to use an Isolated Charger rather than non isolated in the prevention of any parasitic drain between circuits at idle. Does that make sense or am I misinterpreting the purpose of that specification?

 

[mikefitz]

it seems more appropriate to use an Isolated Charger rather than non isolated in the prevention of any parasitic drain

There should be no difference. The starter battery will be negative connected to chassis/body and your service battery negative, for safety, will/should be connected to body/chassis. Thus having the more expensive isolated charger is not required.

My tests on Orion chargers ( non isolated) show that current flow on the input or output when the unit is idle, is less than 1mA.

One aspect regarding the Orion range of chargers is that they need good airflow. If allowed to get hot the output power is reduced.

Mike

 

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Thanks Mike!

 

[Seven30]

A DC-DC charger look like the only way to go with modern charging systems controlled by the vehicle ECU even though they are somewhat limited in power. But if you have an older vehicle with conventional Alternator/regulator you may have more options such as running a 24volt alternator and lithium capable regulator to charge house system directly(through protection system). The DC-DC charger keeps vehicle charged. 24>12 is more efficient than 12>24 as well.