House and Engine Battery -Update 2-Surge? REGEN threat!

Mex, do you mean they can be charged together in parallel no problem, but should not be floated together in parallel or what?

I don't know if there is a threat from eddies and all that or not. Or is it only between flooded batts in parallel and it would not happen at all between an Li and a flooded or an Si and a flooded. Or what? Thanks.

I caught the miscommunication BFL. He meant charging no issues, separated (isolated) same thing no issues. The parallel was stopped.

Unless finish charging voltages are different or amperage tolerances are limited, who cares? Certainly not the batteries.

A note too often ommited, is the engine battery suffers extremely high temperatures. Even at 13.4 volts temperature correct for the proper voltage at 125 degrees F and your eyes will open wide.

I hate to think what my bus batteries went through when it got to 122F at Ciudad Obregon, Mex.

You're still on Vancouver Island, right? Battery Paradise.

if you wanted to keep the ability to charge wit your alternator one of these would do it properly

Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger

Renogy Board 40A DC to DC Battery Charger Using Multi-stage Charging

time2roll wrote:
Still no effect while charging. In use they are separated. No issues.

No, they would be in parallel while charging or floating driving or parked. (It is a Chev with Pin 4 always live unless you pull the fuse for that or yank the 7-pin connection out)

There is something about weird things that can happen inside and between dissimilar batteries in parallel that might be more so when the batteries are very different as with Li or Si and "ordinary" flooded or AGM types.

I wonder what the Li guys are doing if anything?

Good idea with the inverter! That would work for the emergency case of a low House battery. I did run a test for that some years ago with a 400w inverter (I still have) clamped to the engine batt in the truck (same truck) while idling and it ran the Vector charger (same charger as in the TC now) at 20 amps (which needs 320w, the running watts for that 400w inverter.) So I can just have that 400w inverter along as a back-up.

Still does not answer the issue of the very different batteries in parallel where supposedly nasty current eddies and all that get going and any other weird stuff that could be damaging.

The charging voltages, amps amount, and charging profiles are the same, so they are not an issue---it is just their being in parallel that could be.

My solution - long:
My Winnebago Fuse on the Ford Transit 350 HD chassis had this issue. The Ford engine alternator uses a new Ford Smart Charge technology to charge the Ford engine battery (2 AGM batteries) . However we Fuse owners have discovered that when the Winnebago Fuse House batteries are connected to the engine alternator system, the Ford Smart Charge regulator never drops charge down from its high 14.7 Volt output level. What this means is that all batteries are constantly being charged high rate for many hours a day while driving. This is a good way to cook and ruin nice AGM batteries, including the Ford chassis batteries. I resolved this issue by adding a simple switch to in the battery solenoid circuit that disconnects the Ford 12 V system totally from the House battery bank when driving. The Ford Smart Charge system now drops down to the 13.7V level as it should when the chassis batteries are full and the House batteries are kept safe - my 200W solar keep them up just fine. Same principle could be applied if one changed out the House batteries to another type.

Still no effect while charging. In use they are separated. No issues.

What you want is a DC-DC battery charger. Just make sure that one of the supported "battery chemistries" is SiO2.


Hmmm ... Quick search did not turn up such a beast ! Worst case, run a 1000W inverter off of the engine battery and power your SiO2 battery charger. You probably should wire a relay in so that the inverter is only powered when the engine is running.