Charging bike battery from camper battery

[Brokenspoke]

Has anyone got a system for charging a 52 volt 14 amphr bike battery from a 12 volt camper battery without going through an AC/DC inverter? I tried the latter (inverter method) but my ebike battery charger just surges (AC voltage from the pure sine wave inverter surges/fluctuates between 95 and 111 volts). So that apparently doesn't work. 'Paxtana' suggested this unit https://www.amazon.com/dp/B01HCL7LEW/ Has anyone had good or bad experiences with this unit? One review said it doesn't work on a 52 volt system. Thanks.

[Daxxie]

My camper has 2X 12V 110Ah Batterys and a solar panel.

I use a Luna charger on a 300W 220V pure sine inverter.
That works great and will charge my battery at a max of 2 to 3A

I also have this 900W DC step Up converter as a backup.
It was quite cheap, it works, but max output @58.8V is around 1A
Not a lot but it does the job.

[Gr8fun]

The 7210a ming he solar boost ontroller can charge from. 12 volt battery or solar panel and is adjustable to almost all e bike batteries. It is inefficient as solar controller.

[Gr8fun]

Just checked that is what paxtana reccomended. Confirmed. Works good.

[Brokenspoke]

Thanks for the suggestions and confirmation on the 7210a solar boost controller. Will keep the post updated on how things work out. Going to give the pure sine wave inverter method another try now that it is back from Renogy using a load such as a mixer or 100 watt light to get it started to see if that will stop the AC voltage fluctuations to my bike battery charger. If that doesn't work, it may become my new boat anchor and I will order the solar boost controller!

[Gr8fun]

I am not sure what size your solar panel is, but directly off my 160 watt panel to a genasun boost controller i get more than 2 amps charge rate to my 52 volt. With the 7210a i only got 1.4 amps.
currently i have panel 100w permanently installed pn bike. Getting 1.4 amp charge. Genasun boost.
Every time you go to a process there are inefficiencies. The panel to ypur charge controller. The battery charging itself is inefficient
then an invertor and 100 watt lite bulb. To another charger. To another battery.
easily more than half your energy is lost.
when i drive, my panel powers a 98 % efficient boost controller directly to my motor. Simple, little waste. I charge while i drive, when parked. Never run out of go juice or waste time charging.

[Unlearn]

when i drive, my panel powers a 98 % efficient boost controller directly to my motor. Simple, little waste. I charge while i drive, when parked. Never run out of go juice or waste time charging.

Please explain what a boost controller is? Can you guide me to getting an affordable car charging setup? I have a deep cycle battery and an inverter right now that’s it.

sorry I’m a noob. How would one hook up 7210a solar boost controller to their ebike battery ? I’m unsure of the connection they have. Would you do it in the same manner as you would a 12v? ThNks

[JPLabs]

A bost controller (DC-DC Boost Converter) can go from low to higher VDC in one box. Fewer stages of conversion would be more efficient, I agree. Going from DC to AC and back is wasteful.

With a BMS, you can charge with a voltage source that's current limited, be it a 120V charger, or a DC power supply.

Hope that helps.

[Gr8fun]

I am looking for my 7210 charge controller before i answer a couple of things. Such as no protection for overdischsrging your lead acid battery. (Inexpensive low voltage cutoff switch).
efficiency at lower voltages.

[Brokenspoke]

I just got my 2000 watt pure sine wave inverter returned from Renogy, supposedly "fully functional". Still same problem with the AC voltage output from the inverter fluctuating from 95 to 110 volts when only the ebike battery charger is plugged in. So I hooked up the blender/mixer (220 watt load) before turning on the ebike battery charger. Still same problem. Blender works fine, battery charger, not so much! It looks like time for plan 'B'; out with the inverter idea ('inefficient' as previously pointed out) and on to the 7210a charge controller idea. Thanks for the 'low voltage cutoff switch' suggestion. I would like to be kind to my 12 volt output battery and to my 52 volt battery pack!

[JPLabs]

Brokenspoke,

I guess I don't yet understand if it actually charges while the AC inverter voltage is fluctuating - does the charger work on the inverter, or refuse to start, or keep cycling, or what?

I never checked my cheap inverter's AC voltage when charging. I don't know how sensitive the chargers are to fluctuation. 95VAC may be too low to run it, i don't know. What did you see?

[Gr8fun]

The 7210 is 10 amp input. That means you will get at best a 2 amp charge rate with it. Using the 12 volt battery. To 52 volt e bike. Only charge to maximum of about 51.7. Not the full 58.8 possible.

[Brokenspoke]

JPLabs;
While the AC output voltage from the inverter is fluctuating the continuous run battery charger cooling fan speed fluctuates wildly. The charger has a red light that turns green once the battery is charged. It will blink/fade in and out between red and green while the fan speed in fluctuating. I only tried to charge the battery once from the inverter while all this was going on, and yes the battery did charge. I didn't want to continue doing this as I wasn't sure if it would damage the battery/charger. Interesting thing is, I just bought a 2 amp bike battery charger, when plugged into the same inverter and charging the battery, the inverter AC output voltage stays at 120 Volts.

[Brokenspoke]

Thanks GR8fun for the advice on the 7210

[JPLabs]

JPLabs;
While the AC output voltage from the inverter is fluctuating the continuous run battery charger cooling fan speed fluctuates wildly. The charger has a red light that turns green once the battery is charged. It will blink/fade in and out between red and green while the fan speed in fluctuating. I only tried to charge the battery once from the inverter while all this was going on, and yes the battery did charge. I didn't want to continue doing this as I wasn't sure if it would damage the battery/charger. Interesting thing is, I just bought a 2 amp bike battery charger, when plugged into the same inverter and charging the battery, the inverter AC output voltage stays at 120 Volts.

I see, thanks for explaining. I wouldn't trust it running like that, either, good call I think.